- Assertion Testing
- Async Hooks
- Buffer
- C++ Addons
- C/C++ Addons - N-API
- Child Processes
- Cluster
- Command Line Options
- Console
- Crypto
- Debugger
- Deprecated APIs
- DNS
- Domain
- Errors
- Events
- File System
- Globals
- HTTP
- HTTPS
- Inspector
- Internationalization
- Modules
- Net
- OS
- Path
- Process
- Punycode
- Query Strings
- Readline
- REPL
- Stream
- String Decoder
- Timers
- TLS/SSL
- Tracing
- TTY
- UDP/Datagram
- URL
- Utilities
- V8
- VM
- ZLIB
Node.js v8.2.1 Documentation
Table of Contents
- About this Documentation
- Usage
- Assert
- assert(value[, message])
- assert.deepEqual(actual, expected[, message])
- assert.deepStrictEqual(actual, expected[, message])
- assert.doesNotThrow(block[, error][, message])
- assert.equal(actual, expected[, message])
- assert.fail(message)
- assert.fail(actual, expected, message, operator)
- assert.ifError(value)
- assert.notDeepEqual(actual, expected[, message])
- assert.notDeepStrictEqual(actual, expected[, message])
- assert.notEqual(actual, expected[, message])
- assert.notStrictEqual(actual, expected[, message])
- assert.ok(value[, message])
- assert.strictEqual(actual, expected[, message])
- assert.throws(block[, error][, message])
- Caveats
- Async Hooks
- Buffer
Buffer.from()
,Buffer.alloc()
, andBuffer.allocUnsafe()
- Buffers and Character Encodings
- Buffers and TypedArray
- Buffers and ES6 iteration
- Class: Buffer
- new Buffer(array)
- new Buffer(arrayBuffer[, byteOffset [, length]])
- new Buffer(buffer)
- new Buffer(size)
- new Buffer(string[, encoding])
- Class Method: Buffer.alloc(size[, fill[, encoding]])
- Class Method: Buffer.allocUnsafe(size)
- Class Method: Buffer.allocUnsafeSlow(size)
- Class Method: Buffer.byteLength(string[, encoding])
- Class Method: Buffer.compare(buf1, buf2)
- Class Method: Buffer.concat(list[, totalLength])
- Class Method: Buffer.from(array)
- Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])
- Class Method: Buffer.from(buffer)
- Class Method: Buffer.from(string[, encoding])
- Class Method: Buffer.from(object[, offsetOrEncoding[, length]])
- Class Method: Buffer.isBuffer(obj)
- Class Method: Buffer.isEncoding(encoding)
- Class Property: Buffer.poolSize
- buf[index]
- buf.buffer
- buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])
- buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])
- buf.entries()
- buf.equals(otherBuffer)
- buf.fill(value[, offset[, end]][, encoding])
- buf.includes(value[, byteOffset][, encoding])
- buf.indexOf(value[, byteOffset][, encoding])
- buf.keys()
- buf.lastIndexOf(value[, byteOffset][, encoding])
- buf.length
- buf.parent
- buf.readDoubleBE(offset[, noAssert])
- buf.readDoubleLE(offset[, noAssert])
- buf.readFloatBE(offset[, noAssert])
- buf.readFloatLE(offset[, noAssert])
- buf.readInt8(offset[, noAssert])
- buf.readInt16BE(offset[, noAssert])
- buf.readInt16LE(offset[, noAssert])
- buf.readInt32BE(offset[, noAssert])
- buf.readInt32LE(offset[, noAssert])
- buf.readIntBE(offset, byteLength[, noAssert])
- buf.readIntLE(offset, byteLength[, noAssert])
- buf.readUInt8(offset[, noAssert])
- buf.readUInt16BE(offset[, noAssert])
- buf.readUInt16LE(offset[, noAssert])
- buf.readUInt32BE(offset[, noAssert])
- buf.readUInt32LE(offset[, noAssert])
- buf.readUIntBE(offset, byteLength[, noAssert])
- buf.readUIntLE(offset, byteLength[, noAssert])
- buf.slice([start[, end]])
- buf.swap16()
- buf.swap32()
- buf.swap64()
- buf.toJSON()
- buf.toString([encoding[, start[, end]]])
- buf.values()
- buf.write(string[, offset[, length]][, encoding])
- buf.writeDoubleBE(value, offset[, noAssert])
- buf.writeDoubleLE(value, offset[, noAssert])
- buf.writeFloatBE(value, offset[, noAssert])
- buf.writeFloatLE(value, offset[, noAssert])
- buf.writeInt8(value, offset[, noAssert])
- buf.writeInt16BE(value, offset[, noAssert])
- buf.writeInt16LE(value, offset[, noAssert])
- buf.writeInt32BE(value, offset[, noAssert])
- buf.writeInt32LE(value, offset[, noAssert])
- buf.writeIntBE(value, offset, byteLength[, noAssert])
- buf.writeIntLE(value, offset, byteLength[, noAssert])
- buf.writeUInt8(value, offset[, noAssert])
- buf.writeUInt16BE(value, offset[, noAssert])
- buf.writeUInt16LE(value, offset[, noAssert])
- buf.writeUInt32BE(value, offset[, noAssert])
- buf.writeUInt32LE(value, offset[, noAssert])
- buf.writeUIntBE(value, offset, byteLength[, noAssert])
- buf.writeUIntLE(value, offset, byteLength[, noAssert])
- buffer.INSPECT_MAX_BYTES
- buffer.kMaxLength
- buffer.transcode(source, fromEnc, toEnc)
- Class: SlowBuffer
- Buffer Constants
- C++ Addons
- N-API
- Basic N-API Data Types
- Error Handling
- Object Lifetime management
- Module registration
- Working with JavaScript Values
- Working with JavaScript Values - Abstract Operations
- Working with JavaScript Properties
- Working with JavaScript Functions
- Object Wrap
- Asynchronous Operations
- Version Management
- Child Process
- Asynchronous Process Creation
- Synchronous Process Creation
- Class: ChildProcess
maxBuffer
and Unicode
- Cluster
- How It Works
- Class: Worker
- Event: 'disconnect'
- Event: 'error'
- Event: 'exit'
- Event: 'listening'
- Event: 'message'
- Event: 'online'
- worker.disconnect()
- worker.exitedAfterDisconnect
- worker.id
- worker.isConnected()
- worker.isDead()
- worker.kill([signal='SIGTERM'])
- worker.process
- worker.send(message[, sendHandle][, callback])
- worker.suicide
- Event: 'disconnect'
- Event: 'exit'
- Event: 'fork'
- Event: 'listening'
- Event: 'message'
- Event: 'online'
- Event: 'setup'
- cluster.disconnect([callback])
- cluster.fork([env])
- cluster.isMaster
- cluster.isWorker
- cluster.schedulingPolicy
- cluster.settings
- cluster.setupMaster([settings])
- cluster.worker
- cluster.workers
- Command Line Options
- Synopsis
- Options
-v
,--version
-h
,--help
-e
,--eval "script"
-p
,--print "script"
-c
,--check
-i
,--interactive
-r
,--require module
--inspect[=[host:]port]
--inspect-brk[=[host:]port]
--inspect-port=[host:]port
--no-deprecation
--trace-deprecation
--throw-deprecation
--pending-deprecation
--no-warnings
--napi-modules
--abort-on-uncaught-exception
--trace-warnings
--redirect-warnings=file
--trace-sync-io
--trace-events-enabled
--trace-event-categories
--zero-fill-buffers
--preserve-symlinks
--track-heap-objects
--prof-process
--v8-options
--tls-cipher-list=list
--enable-fips
--force-fips
--openssl-config=file
--use-openssl-ca
,--use-bundled-ca
--icu-data-dir=file
-
--
- Environment Variables
NODE_DEBUG=module[,…]
NODE_PATH=path[:…]
NODE_DISABLE_COLORS=1
NODE_ICU_DATA=file
NODE_NO_WARNINGS=1
NODE_OPTIONS=options...
NODE_PENDING_DEPRECATION=1
NODE_PRESERVE_SYMLINKS=1
NODE_REPL_HISTORY=file
NODE_EXTRA_CA_CERTS=file
OPENSSL_CONF=file
SSL_CERT_DIR=dir
SSL_CERT_FILE=file
NODE_REDIRECT_WARNINGS=file
- Console
- Class: Console
- new Console(stdout[, stderr])
- console.assert(value[, message][, ...args])
- console.dir(obj[, options])
- console.error([data][, ...args])
- console.info([data][, ...args])
- console.log([data][, ...args])
- console.time(label)
- console.timeEnd(label)
- console.trace([message][, ...args])
- console.warn([data][, ...args])
- Class: Console
- Crypto
- Determining if crypto support is unavailable
- Class: Certificate
- Class: Cipher
- Class: Decipher
- Class: DiffieHellman
- diffieHellman.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])
- diffieHellman.generateKeys([encoding])
- diffieHellman.getGenerator([encoding])
- diffieHellman.getPrime([encoding])
- diffieHellman.getPrivateKey([encoding])
- diffieHellman.getPublicKey([encoding])
- diffieHellman.setPrivateKey(privateKey[, encoding])
- diffieHellman.setPublicKey(publicKey[, encoding])
- diffieHellman.verifyError
- Class: ECDH
- Class: Hash
- Class: Hmac
- Class: Sign
- Class: Verify
crypto
module methods and properties- crypto.constants
- crypto.DEFAULT_ENCODING
- crypto.fips
- crypto.createCipher(algorithm, password)
- crypto.createCipheriv(algorithm, key, iv)
- crypto.createCredentials(details)
- crypto.createDecipher(algorithm, password)
- crypto.createDecipheriv(algorithm, key, iv)
- crypto.createDiffieHellman(prime[, primeEncoding][, generator][, generatorEncoding])
- crypto.createDiffieHellman(primeLength[, generator])
- crypto.createECDH(curveName)
- crypto.createHash(algorithm)
- crypto.createHmac(algorithm, key)
- crypto.createSign(algorithm)
- crypto.createVerify(algorithm)
- crypto.getCiphers()
- crypto.getCurves()
- crypto.getDiffieHellman(groupName)
- crypto.getHashes()
- crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)
- crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)
- crypto.privateDecrypt(privateKey, buffer)
- crypto.privateEncrypt(privateKey, buffer)
- crypto.publicDecrypt(publicKey, buffer)
- crypto.publicEncrypt(publicKey, buffer)
- crypto.randomBytes(size[, callback])
- crypto.randomFillSync(buffer[, offset][, size])
- crypto.randomFill(buffer[, offset][, size], callback)
- crypto.setEngine(engine[, flags])
- crypto.timingSafeEqual(a, b)
- Notes
- Crypto Constants
- Debugger
- Deprecated APIs
- Un-deprecation
- List of Deprecated APIs
- DEP0001: http.OutgoingMessage.prototype.flush
- DEP0002: require('_linklist')
- DEP0003: _writableState.buffer
- DEP0004: CryptoStream.prototype.readyState
- DEP0005: Buffer() constructor
- DEP0006: child_process options.customFds
- DEP0007: cluster worker.suicide
- DEP0008: require('constants')
- DEP0009: crypto.pbkdf2 without digest
- DEP0010: crypto.createCredentials
- DEP0011: crypto.Credentials
- DEP0012: Domain.dispose
- DEP0013: fs async function without callback
- DEP0014: fs.read legacy String interface
- DEP0015: fs.readSync legacy String interface
- DEP0016: GLOBAL/root
- DEP0017: Intl.v8BreakIterator
- DEP0018: Unhandled promise rejections
- DEP0019: require('.') resolved outside directory
- DEP0020: Server.connections
- DEP0021: Server.listenFD
- DEP0022: os.tmpDir()
- DEP0023: os.getNetworkInterfaces()
- DEP0024: REPLServer.prototype.convertToContext()
- DEP0025: require('sys')
- DEP0026: util.print()
- DEP0027: util.puts()
- DEP0028: util.debug()
- DEP0029: util.error()
- DEP0030: SlowBuffer
- DEP0031: ecdh.setPublicKey()
- DEP0032: domain module
- DEP0033: EventEmitter.listenerCount()
- DEP0034: fs.exists(path, callback)
- DEP0035: fs.lchmod(path, mode, callback)
- DEP0036: fs.lchmodSync(path, mode)
- DEP0037: fs.lchown(path, uid, gid, callback)
- DEP0038: fs.lchownSync(path, uid, gid)
- DEP0039: require.extensions
- DEP0040: punycode module
- DEP0041: NODE_REPL_HISTORY_FILE environment variable
- DEP0042: tls.CryptoStream
- DEP0043: tls.SecurePair
- DEP0044: util.isArray()
- DEP0045: util.isBoolean()
- DEP0046: util.isBuffer()
- DEP0047: util.isDate()
- DEP0048: util.isError()
- DEP0049: util.isFunction()
- DEP0050: util.isNull()
- DEP0051: util.isNullOrUndefined()
- DEP0052: util.isNumber()
- DEP0053 util.isObject()
- DEP0054: util.isPrimitive()
- DEP0055: util.isRegExp()
- DEP0056: util.isString()
- DEP0057: util.isSymbol()
- DEP0058: util.isUndefined()
- DEP0059: util.log()
- DEP0060: util._extend()
- DEP0061: fs.SyncWriteStream
- DEP0062: node --debug
- DEP0063: ServerResponse.prototype.writeHeader()
- DEP0064: tls.createSecurePair()
- DEP0065: repl.REPL_MODE_MAGIC and NODE_REPL_MODE=magic
- DEP0066: outgoingMessage._headers, outgoingMessage._headerNames
- DEP0067: OutgoingMessage.prototype._renderHeaders
- DEP0068: node debug
- DEP0069: vm.runInDebugContext(string)
- DEP0070: async_hooks.currentId()
- DEP0071: async_hooks.triggerId()
- DEP0072: async_hooks.AsyncResource.triggerId()
- DNS
- dns.getServers()
- dns.lookup(hostname[, options], callback)
- dns.lookupService(address, port, callback)
- dns.resolve(hostname[, rrtype], callback)
- dns.resolve4(hostname[, options], callback)
- dns.resolve6(hostname[, options], callback)
- dns.resolveCname(hostname, callback)
- dns.resolveMx(hostname, callback)
- dns.resolveNaptr(hostname, callback)
- dns.resolveNs(hostname, callback)
- dns.resolvePtr(hostname, callback)
- dns.resolveSoa(hostname, callback)
- dns.resolveSrv(hostname, callback)
- dns.resolveTxt(hostname, callback)
- dns.resolveAny(hostname, callback)
- dns.reverse(ip, callback)
- dns.setServers(servers)
- Error codes
- Implementation considerations
- Domain
- Errors
- Error Propagation and Interception
- Class: Error
- Class: RangeError
- Class: ReferenceError
- Class: SyntaxError
- Class: TypeError
- Exceptions vs. Errors
- System Errors
- Node.js Error Codes
- ERR_ARG_NOT_ITERABLE
- ERR_FALSY_VALUE_REJECTION
- ERR_INVALID_ARG_TYPE
- ERR_INVALID_CALLBACK
- ERR_INVALID_FILE_URL_HOST
- ERR_INVALID_FILE_URL_PATH
- ERR_INVALID_HANDLE_TYPE
- ERR_INVALID_OPT_VALUE
- ERR_INVALID_SYNC_FORK_INPUT
- ERR_INVALID_THIS
- ERR_INVALID_TUPLE
- ERR_INVALID_URL
- ERR_INVALID_URL_SCHEME
- ERR_IPC_CHANNEL_CLOSED
- ERR_IPC_DISCONNECTED
- ERR_IPC_ONE_PIPE
- ERR_IPC_SYNC_FORK
- ERR_MISSING_ARGS
- ERR_SOCKET_ALREADY_BOUND
- ERR_SOCKET_BAD_PORT
- ERR_SOCKET_BAD_TYPE
- ERR_SOCKET_CANNOT_SEND
- ERR_SOCKET_DGRAM_NOT_RUNNING
- ERR_STDERR_CLOSE
- ERR_STDOUT_CLOSE
- ERR_UNKNOWN_BUILTIN_MODULE
- ERR_UNKNOWN_SIGNAL
- ERR_UNKNOWN_STDIN_TYPE
- ERR_UNKNOWN_STREAM_TYPE
- Events
- Passing arguments and
this
to listeners - Asynchronous vs. Synchronous
- Handling events only once
- Error events
- Class: EventEmitter
- Event: 'newListener'
- Event: 'removeListener'
- EventEmitter.listenerCount(emitter, eventName)
- EventEmitter.defaultMaxListeners
- emitter.addListener(eventName, listener)
- emitter.emit(eventName[, ...args])
- emitter.eventNames()
- emitter.getMaxListeners()
- emitter.listenerCount(eventName)
- emitter.listeners(eventName)
- emitter.on(eventName, listener)
- emitter.once(eventName, listener)
- emitter.prependListener(eventName, listener)
- emitter.prependOnceListener(eventName, listener)
- emitter.removeAllListeners([eventName])
- emitter.removeListener(eventName, listener)
- emitter.setMaxListeners(n)
- Passing arguments and
- File System
- WHATWG URL object support
- Buffer API
- Class: fs.FSWatcher
- Class: fs.ReadStream
- Class: fs.Stats
- Class: fs.WriteStream
- fs.access(path[, mode], callback)
- fs.accessSync(path[, mode])
- fs.appendFile(file, data[, options], callback)
- fs.appendFileSync(file, data[, options])
- fs.chmod(path, mode, callback)
- fs.chmodSync(path, mode)
- fs.chown(path, uid, gid, callback)
- fs.chownSync(path, uid, gid)
- fs.close(fd, callback)
- fs.closeSync(fd)
- fs.constants
- fs.createReadStream(path[, options])
- fs.createWriteStream(path[, options])
- fs.exists(path, callback)
- fs.existsSync(path)
- fs.fchmod(fd, mode, callback)
- fs.fchmodSync(fd, mode)
- fs.fchown(fd, uid, gid, callback)
- fs.fchownSync(fd, uid, gid)
- fs.fdatasync(fd, callback)
- fs.fdatasyncSync(fd)
- fs.fstat(fd, callback)
- fs.fstatSync(fd)
- fs.fsync(fd, callback)
- fs.fsyncSync(fd)
- fs.ftruncate(fd[, len], callback)
- fs.ftruncateSync(fd[, len])
- fs.futimes(fd, atime, mtime, callback)
- fs.futimesSync(fd, atime, mtime)
- fs.lchmod(path, mode, callback)
- fs.lchmodSync(path, mode)
- fs.lchown(path, uid, gid, callback)
- fs.lchownSync(path, uid, gid)
- fs.link(existingPath, newPath, callback)
- fs.linkSync(existingPath, newPath)
- fs.lstat(path, callback)
- fs.lstatSync(path)
- fs.mkdir(path[, mode], callback)
- fs.mkdirSync(path[, mode])
- fs.mkdtemp(prefix[, options], callback)
- fs.mkdtempSync(prefix[, options])
- fs.open(path, flags[, mode], callback)
- fs.openSync(path, flags[, mode])
- fs.read(fd, buffer, offset, length, position, callback)
- fs.readdir(path[, options], callback)
- fs.readdirSync(path[, options])
- fs.readFile(path[, options], callback)
- fs.readFileSync(path[, options])
- fs.readlink(path[, options], callback)
- fs.readlinkSync(path[, options])
- fs.readSync(fd, buffer, offset, length, position)
- fs.realpath(path[, options], callback)
- fs.realpathSync(path[, options])
- fs.rename(oldPath, newPath, callback)
- fs.renameSync(oldPath, newPath)
- fs.rmdir(path, callback)
- fs.rmdirSync(path)
- fs.stat(path, callback)
- fs.statSync(path)
- fs.symlink(target, path[, type], callback)
- fs.symlinkSync(target, path[, type])
- fs.truncate(path[, len], callback)
- fs.truncateSync(path[, len])
- fs.unlink(path, callback)
- fs.unlinkSync(path)
- fs.unwatchFile(filename[, listener])
- fs.utimes(path, atime, mtime, callback)
- fs.utimesSync(path, atime, mtime)
- fs.watch(filename[, options][, listener])
- fs.watchFile(filename[, options], listener)
- fs.write(fd, buffer[, offset[, length[, position]]], callback)
- fs.write(fd, string[, position[, encoding]], callback)
- fs.writeFile(file, data[, options], callback)
- fs.writeFileSync(file, data[, options])
- fs.writeSync(fd, buffer[, offset[, length[, position]]])
- fs.writeSync(fd, string[, position[, encoding]])
- FS Constants
- Global Objects
- HTTP
- Class: http.Agent
- Class: http.ClientRequest
- Event: 'abort'
- Event: 'aborted'
- Event: 'connect'
- Event: 'continue'
- Event: 'response'
- Event: 'socket'
- Event: 'upgrade'
- request.abort()
- request.aborted
- request.connection
- request.end([data[, encoding]][, callback])
- request.flushHeaders()
- request.setNoDelay([noDelay])
- request.setSocketKeepAlive([enable][, initialDelay])
- request.setTimeout(timeout[, callback])
- request.socket
- request.write(chunk[, encoding][, callback])
- Class: http.Server
- Event: 'checkContinue'
- Event: 'checkExpectation'
- Event: 'clientError'
- Event: 'close'
- Event: 'connect'
- Event: 'connection'
- Event: 'request'
- Event: 'upgrade'
- server.close([callback])
- server.listen(handle[, callback])
- server.listen(path[, callback])
- server.listen([port][, hostname][, backlog][, callback])
- server.listening
- server.maxHeadersCount
- server.setTimeout([msecs][, callback])
- server.timeout
- server.keepAliveTimeout
- Class: http.ServerResponse
- Event: 'close'
- Event: 'finish'
- response.addTrailers(headers)
- response.connection
- response.end([data][, encoding][, callback])
- response.finished
- response.getHeader(name)
- response.getHeaderNames()
- response.getHeaders()
- response.hasHeader(name)
- response.headersSent
- response.removeHeader(name)
- response.sendDate
- response.setHeader(name, value)
- response.setTimeout(msecs[, callback])
- response.socket
- response.statusCode
- response.statusMessage
- response.write(chunk[, encoding][, callback])
- response.writeContinue()
- response.writeHead(statusCode[, statusMessage][, headers])
- Class: http.IncomingMessage
- http.METHODS
- http.STATUS_CODES
- http.createServer([requestListener])
- http.get(options[, callback])
- http.globalAgent
- http.request(options[, callback])
- HTTPS
- Inspector
- Internationalization Support
- Modules
- Net
- IPC Support
- Class: net.Server
- new net.Server([options][, connectionListener])
- Class: net.Socket
- new net.Socket([options])
- Event: 'close'
- Event: 'connect'
- Event: 'data'
- Event: 'drain'
- Event: 'end'
- Event: 'error'
- Event: 'lookup'
- Event: 'timeout'
- socket.address()
- socket.bufferSize
- socket.bytesRead
- socket.bytesWritten
- socket.connect()
- socket.connecting
- socket.destroy([exception])
- socket.destroyed
- socket.end([data][, encoding])
- socket.localAddress
- socket.localPort
- socket.pause()
- socket.ref()
- socket.remoteAddress
- socket.remoteFamily
- socket.remotePort
- socket.resume()
- socket.setEncoding([encoding])
- socket.setKeepAlive([enable][, initialDelay])
- socket.setNoDelay([noDelay])
- socket.setTimeout(timeout[, callback])
- socket.unref()
- socket.write(data[, encoding][, callback])
- net.connect()
- net.createConnection()
- net.createServer([options][, connectionListener])
- net.isIP(input)
- net.isIPv4(input)
- net.isIPv6(input)
- OS
- Path
- Process
- Process Events
- process.abort()
- process.arch
- process.argv
- process.argv0
- process.channel
- process.chdir(directory)
- process.config
- process.connected
- process.cpuUsage([previousValue])
- process.cwd()
- process.disconnect()
- process.emitWarning(warning[, options])
- process.emitWarning(warning[, type[, code]][, ctor])
- process.env
- process.execArgv
- process.execPath
- process.exit([code])
- process.exitCode
- process.getegid()
- process.geteuid()
- process.getgid()
- process.getgroups()
- process.getuid()
- process.hrtime([time])
- process.initgroups(user, extra_group)
- process.kill(pid[, signal])
- process.mainModule
- process.memoryUsage()
- process.nextTick(callback[, ...args])
- process.pid
- process.platform
- process.release
- process.send(message[, sendHandle[, options]][, callback])
- process.setegid(id)
- process.seteuid(id)
- process.setgid(id)
- process.setgroups(groups)
- process.setuid(id)
- process.stderr
- process.stdin
- process.stdout
- process.title
- process.umask([mask])
- process.uptime()
- process.version
- process.versions
- Exit Codes
- Punycode
- Query String
- Readline
- REPL
- Stream
- Organization of this Document
- Types of Streams
- API for Stream Consumers
- Writable Streams
- Readable Streams
- Two Modes
- Three States
- Choose One
- Class: stream.Readable
- Event: 'close'
- Event: 'data'
- Event: 'end'
- Event: 'error'
- Event: 'readable'
- readable.isPaused()
- readable.pause()
- readable.pipe(destination[, options])
- readable.read([size])
- readable.resume()
- readable.setEncoding(encoding)
- readable.unpipe([destination])
- readable.unshift(chunk)
- readable.wrap(stream)
- readable.destroy([error])
- Duplex and Transform Streams
- API for Stream Implementers
- Additional Notes
- String Decoder
- Timers
- TLS (SSL)
- TLS/SSL Concepts
- Modifying the Default TLS Cipher suite
- Class: tls.Server
- Event: 'newSession'
- Event: 'OCSPRequest'
- Event: 'resumeSession'
- Event: 'secureConnection'
- Event: 'tlsClientError'
- server.addContext(hostname, context)
- server.address()
- server.close([callback])
- server.connections
- server.getTicketKeys()
- server.listen(port[, hostname][, callback])
- server.setTicketKeys(keys)
- Class: tls.TLSSocket
- new tls.TLSSocket(socket[, options])
- Event: 'OCSPResponse'
- Event: 'secureConnect'
- tlsSocket.address()
- tlsSocket.authorizationError
- tlsSocket.authorized
- tlsSocket.encrypted
- tlsSocket.getCipher()
- tlsSocket.getEphemeralKeyInfo()
- tlsSocket.getPeerCertificate([detailed])
- tlsSocket.getProtocol()
- tlsSocket.getSession()
- tlsSocket.getTLSTicket()
- tlsSocket.localAddress
- tlsSocket.localPort
- tlsSocket.remoteAddress
- tlsSocket.remoteFamily
- tlsSocket.remotePort
- tlsSocket.renegotiate(options, callback)
- tlsSocket.setMaxSendFragment(size)
- tls.connect(options[, callback])
- tls.connect(path[, options][, callback])
- tls.connect(port[, host][, options][, callback])
- tls.createSecureContext(options)
- tls.createServer([options][, secureConnectionListener])
- tls.getCiphers()
- tls.DEFAULT_ECDH_CURVE
- Deprecated APIs
- Tracing
- TTY
- UDP / Datagram Sockets
- Class: dgram.Socket
- Event: 'close'
- Event: 'error'
- Event: 'listening'
- Event: 'message'
- socket.addMembership(multicastAddress[, multicastInterface])
- socket.address()
- socket.bind([port][, address][, callback])
- socket.bind(options[, callback])
- socket.close([callback])
- socket.dropMembership(multicastAddress[, multicastInterface])
- socket.ref()
- socket.send(msg, [offset, length,] port [, address] [, callback])
- socket.setBroadcast(flag)
- socket.setMulticastLoopback(flag)
- socket.setMulticastTTL(ttl)
- socket.setTTL(ttl)
- socket.unref()
- Change to asynchronous
socket.bind()
behavior
dgram
module functions
- Class: dgram.Socket
- URL
- URL Strings and URL Objects
- The WHATWG URL API
- Class: URL
- Class: URLSearchParams
- Constructor: new URLSearchParams()
- Constructor: new URLSearchParams(string)
- Constructor: new URLSearchParams(obj)
- Constructor: new URLSearchParams(iterable)
- urlSearchParams.append(name, value)
- urlSearchParams.delete(name)
- urlSearchParams.entries()
- urlSearchParams.forEach(fn[, thisArg])
- urlSearchParams.get(name)
- urlSearchParams.getAll(name)
- urlSearchParams.has(name)
- urlSearchParams.keys()
- urlSearchParams.set(name, value)
- urlSearchParams.sort()
- urlSearchParams.toString()
- urlSearchParams.values()
- urlSearchParams[@@iterator]()
- url.domainToASCII(domain)
- url.domainToUnicode(domain)
- url.format(URL[, options])
- Legacy URL API
- Percent-Encoding in URLs
- Util
- util.callbackify(original)
- util.debuglog(section)
- util.deprecate(function, string)
- util.format(format[, ...args])
- util.inherits(constructor, superConstructor)
- util.inspect(object[, options])
- util.promisify(original)
- Deprecated APIs
- util._extend(target, source)
- util.debug(string)
- util.error([...strings])
- util.isArray(object)
- util.isBoolean(object)
- util.isBuffer(object)
- util.isDate(object)
- util.isError(object)
- util.isFunction(object)
- util.isNull(object)
- util.isNullOrUndefined(object)
- util.isNumber(object)
- util.isObject(object)
- util.isPrimitive(object)
- util.isRegExp(object)
- util.isString(object)
- util.isSymbol(object)
- util.isUndefined(object)
- util.log(string)
- util.print([...strings])
- util.puts([...strings])
- V8
- v8.cachedDataVersionTag()
- v8.getHeapSpaceStatistics()
- v8.getHeapStatistics()
- v8.setFlagsFromString(string)
- Serialization API
- v8.serialize(value)
- v8.deserialize(buffer)
- class: v8.Serializer
- new Serializer()
- serializer.writeHeader()
- serializer.writeValue(value)
- serializer.releaseBuffer()
- serializer.transferArrayBuffer(id, arrayBuffer)
- serializer.writeUint32(value)
- serializer.writeUint64(hi, lo)
- serializer.writeDouble(value)
- serializer.writeRawBytes(buffer)
- serializer._writeHostObject(object)
- serializer._getDataCloneError(message)
- serializer._getSharedArrayBufferId(sharedArrayBuffer)
- serializer._setTreatArrayBufferViewsAsHostObjects(flag)
- class: v8.Deserializer
- new Deserializer(buffer)
- deserializer.readHeader()
- deserializer.readValue()
- deserializer.transferArrayBuffer(id, arrayBuffer)
- deserializer.getWireFormatVersion()
- deserializer.readUint32()
- deserializer.readUint64()
- deserializer.readDouble()
- deserializer.readRawBytes(length)
- deserializer._readHostObject()
- class: v8.DefaultSerializer
- class: v8.DefaultDeserializer
- VM (Executing JavaScript)
- Class: vm.Script
- vm.createContext([sandbox])
- vm.isContext(sandbox)
- vm.runInContext(code, contextifiedSandbox[, options])
- vm.runInDebugContext(code)
- vm.runInNewContext(code[, sandbox][, options])
- vm.runInThisContext(code[, options])
- Example: Running an HTTP Server within a VM
- What does it mean to "contextify" an object?
- Zlib
- Compressing HTTP requests and responses
- Memory Usage Tuning
- Flushing
- Constants
- Class Options
- Class: zlib.Deflate
- Class: zlib.DeflateRaw
- Class: zlib.Gunzip
- Class: zlib.Gzip
- Class: zlib.Inflate
- Class: zlib.InflateRaw
- Class: zlib.Unzip
- Class: zlib.Zlib
- zlib.constants
- zlib.createDeflate([options])
- zlib.createDeflateRaw([options])
- zlib.createGunzip([options])
- zlib.createGzip([options])
- zlib.createInflate([options])
- zlib.createInflateRaw([options])
- zlib.createUnzip([options])
- Convenience Methods
- zlib.deflate(buffer[, options], callback)
- zlib.deflateSync(buffer[, options])
- zlib.deflateRaw(buffer[, options], callback)
- zlib.deflateRawSync(buffer[, options])
- zlib.gunzip(buffer[, options], callback)
- zlib.gunzipSync(buffer[, options])
- zlib.gzip(buffer[, options], callback)
- zlib.gzipSync(buffer[, options])
- zlib.inflate(buffer[, options], callback)
- zlib.inflateSync(buffer[, options])
- zlib.inflateRaw(buffer[, options], callback)
- zlib.inflateRawSync(buffer[, options])
- zlib.unzip(buffer[, options], callback)
- zlib.unzipSync(buffer[, options])
About this Documentation#
The goal of this documentation is to comprehensively explain the Node.js API, both from a reference as well as a conceptual point of view. Each section describes a built-in module or high-level concept.
Where appropriate, property types, method arguments, and the arguments provided to event handlers are detailed in a list underneath the topic heading.
Every .html
document has a corresponding .json
document presenting
the same information in a structured manner. This feature is
experimental, and added for the benefit of IDEs and other utilities that
wish to do programmatic things with the documentation.
Every .html
and .json
file is generated based on the corresponding
.md
file in the doc/api/
folder in Node.js's source tree. The
documentation is generated using the tools/doc/generate.js
program.
The HTML template is located at doc/template.html
.
If errors are found in this documentation, please submit an issue or see the contributing guide for directions on how to submit a patch.
Stability Index#
Throughout the documentation are indications of a section's stability. The Node.js API is still somewhat changing, and as it matures, certain parts are more reliable than others. Some are so proven, and so relied upon, that they are unlikely to ever change at all. Others are brand new and experimental, or known to be hazardous and in the process of being redesigned.
The stability indices are as follows:
Stability: 0 - Deprecated This feature is known to be problematic, and changes are planned. Do not rely on it. Use of the feature may cause warnings. Backwards compatibility should not be expected.
Stability: 1 - Experimental This feature is subject to change, and is gated by a command line flag. It may change or be removed in future versions.
Stability: 2 - Stable The API has proven satisfactory. Compatibility with the npm ecosystem is a high priority, and will not be broken unless absolutely necessary.
JSON Output#
Stability: 1 - Experimental
Every HTML file in the markdown has a corresponding JSON file with the same data.
This feature was added in Node.js v0.6.12. It is experimental.
Syscalls and man pages#
System calls like open(2) and read(2) define the interface between user programs
and the underlying operating system. Node functions which simply wrap a syscall,
like fs.open()
, will document that. The docs link to the corresponding man
pages (short for manual pages) which describe how the syscalls work.
Caveat: some syscalls, like lchown(2), are BSD-specific. That means, for
example, that fs.lchown()
only works on macOS and other BSD-derived systems,
and is not available on Linux.
Most Unix syscalls have Windows equivalents, but behavior may differ on Windows relative to Linux and macOS. For an example of the subtle ways in which it's sometimes impossible to replace Unix syscall semantics on Windows, see Node issue 4760.
Usage#
node [options] [v8 options] [script.js | -e "script" | - ] [arguments]
Please see the Command Line Options document for information about different options and ways to run scripts with Node.js.
Example#
An example of a web server written with Node.js which responds with
'Hello World'
:
const http = require('http');
const hostname = '127.0.0.1';
const port = 3000;
const server = http.createServer((req, res) => {
res.statusCode = 200;
res.setHeader('Content-Type', 'text/plain');
res.end('Hello World\n');
});
server.listen(port, hostname, () => {
console.log(`Server running at http://${hostname}:${port}/`);
});
To run the server, put the code into a file called example.js
and execute
it with Node.js:
$ node example.js
Server running at http://127.0.0.1:3000/
All of the examples in the documentation can be run similarly.
Assert#
Stability: 2 - Stable
The assert
module provides a simple set of assertion tests that can be used to
test invariants.
assert(value[, message])#
value
<any>message
<any>
An alias of assert.ok()
.
assert.deepEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests for deep equality between the actual
and expected
parameters.
Primitive values are compared with the Abstract Equality Comparison
( ==
).
Only enumerable "own" properties are considered. The
assert.deepEqual()
implementation does not test the
[[Prototype]]
of objects, attached symbols, or
non-enumerable properties — for such checks, consider using
assert.deepStrictEqual()
instead. This can lead to some
potentially surprising results. For example, the following example does not
throw an AssertionError
because the properties on the Error
object are
not enumerable:
// WARNING: This does not throw an AssertionError!
assert.deepEqual(Error('a'), Error('b'));
An exception is made for Map
and Set
. Maps and Sets have their
contained items compared too, as expected.
"Deep" equality means that the enumerable "own" properties of child objects are evaluated also:
const assert = require('assert');
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.deepEqual(obj1, obj1);
// OK, object is equal to itself
assert.deepEqual(obj1, obj2);
// AssertionError: { a: { b: 1 } } deepEqual { a: { b: 2 } }
// values of b are different
assert.deepEqual(obj1, obj3);
// OK, objects are equal
assert.deepEqual(obj1, obj4);
// AssertionError: { a: { b: 1 } } deepEqual {}
// Prototypes are ignored
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.deepStrictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Generally identical to assert.deepEqual()
with three exceptions:
- Primitive values are compared using the Strict Equality Comparison
(
===
). Set values and Map keys are compared using the SameValueZero comparison. (Which means they are free of the caveats). [[Prototype]]
of objects are compared using the Strict Equality Comparison too.- Type tags of objects should be the same.
const assert = require('assert');
assert.deepEqual({ a: 1 }, { a: '1' });
// OK, because 1 == '1'
assert.deepStrictEqual({ a: 1 }, { a: '1' });
// AssertionError: { a: 1 } deepStrictEqual { a: '1' }
// because 1 !== '1' using strict equality
// The following objects don't have own properties
const date = new Date();
const object = {};
const fakeDate = {};
Object.setPrototypeOf(fakeDate, Date.prototype);
assert.deepEqual(object, fakeDate);
// OK, doesn't check [[Prototype]]
assert.deepStrictEqual(object, fakeDate);
// AssertionError: {} deepStrictEqual Date {}
// Different [[Prototype]]
assert.deepEqual(date, fakeDate);
// OK, doesn't check type tags
assert.deepStrictEqual(date, fakeDate);
// AssertionError: 2017-03-11T14:25:31.849Z deepStrictEqual Date {}
// Different type tags
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.doesNotThrow(block[, error][, message])#
block
<Function>error
<RegExp> | <Function>message
<any>
Asserts that the function block
does not throw an error. See
assert.throws()
for more details.
When assert.doesNotThrow()
is called, it will immediately call the block
function.
If an error is thrown and it is the same type as that specified by the error
parameter, then an AssertionError
is thrown. If the error is of a different
type, or if the error
parameter is undefined, the error is propagated back
to the caller.
The following, for instance, will throw the TypeError
because there is no
matching error type in the assertion:
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
SyntaxError
);
However, the following will result in an AssertionError
with the message
'Got unwanted exception (TypeError)..':
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError
);
If an AssertionError
is thrown and a value is provided for the message
parameter, the value of message
will be appended to the AssertionError
message:
assert.doesNotThrow(
() => {
throw new TypeError('Wrong value');
},
TypeError,
'Whoops'
);
// Throws: AssertionError: Got unwanted exception (TypeError). Whoops
assert.equal(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests shallow, coercive equality between the actual
and expected
parameters
using the Abstract Equality Comparison ( ==
).
const assert = require('assert');
assert.equal(1, 1);
// OK, 1 == 1
assert.equal(1, '1');
// OK, 1 == '1'
assert.equal(1, 2);
// AssertionError: 1 == 2
assert.equal({ a: { b: 1 } }, { a: { b: 1 } });
//AssertionError: { a: { b: 1 } } == { a: { b: 1 } }
If the values are not equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.fail(message)#
assert.fail(actual, expected, message, operator)#
actual
<any>expected
<any>message
<any>operator
<string> (default: '!=')
Throws an AssertionError
. If message
is falsy, the error message is set as
the values of actual
and expected
separated by the provided operator
.
Otherwise, the error message is the value of message
.
const assert = require('assert');
assert.fail(1, 2, undefined, '>');
// AssertionError: 1 > 2
assert.fail(1, 2, 'whoops', '>');
// AssertionError: whoops
assert.fail('boom');
// AssertionError: boom
assert.fail('a', 'b');
// AssertionError: 'a' != 'b'
assert.ifError(value)#
value
<any>
Throws value
if value
is truthy. This is useful when testing the error
argument in callbacks.
const assert = require('assert');
assert.ifError(0);
// OK
assert.ifError(1);
// Throws 1
assert.ifError('error');
// Throws 'error'
assert.ifError(new Error());
// Throws Error
assert.notDeepEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests for any deep inequality. Opposite of assert.deepEqual()
.
const assert = require('assert');
const obj1 = {
a: {
b: 1
}
};
const obj2 = {
a: {
b: 2
}
};
const obj3 = {
a: {
b: 1
}
};
const obj4 = Object.create(obj1);
assert.notDeepEqual(obj1, obj1);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj2);
// OK, obj1 and obj2 are not deeply equal
assert.notDeepEqual(obj1, obj3);
// AssertionError: { a: { b: 1 } } notDeepEqual { a: { b: 1 } }
assert.notDeepEqual(obj1, obj4);
// OK, obj1 and obj2 are not deeply equal
If the values are deeply equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.notDeepStrictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests for deep strict inequality. Opposite of assert.deepStrictEqual()
.
const assert = require('assert');
assert.notDeepEqual({ a: 1 }, { a: '1' });
// AssertionError: { a: 1 } notDeepEqual { a: '1' }
assert.notDeepStrictEqual({ a: 1 }, { a: '1' });
// OK
If the values are deeply and strictly equal, an AssertionError
is thrown
with a message
property set equal to the value of the message
parameter. If
the message
parameter is undefined, a default error message is assigned.
assert.notEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests shallow, coercive inequality with the Abstract Equality Comparison
( !=
).
const assert = require('assert');
assert.notEqual(1, 2);
// OK
assert.notEqual(1, 1);
// AssertionError: 1 != 1
assert.notEqual(1, '1');
// AssertionError: 1 != '1'
If the values are equal, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined, a default error message is assigned.
assert.notStrictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests strict inequality as determined by the Strict Equality Comparison
( !==
).
const assert = require('assert');
assert.notStrictEqual(1, 2);
// OK
assert.notStrictEqual(1, 1);
// AssertionError: 1 !== 1
assert.notStrictEqual(1, '1');
// OK
If the values are strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned.
assert.ok(value[, message])#
value
<any>message
<any>
Tests if value
is truthy. It is equivalent to
assert.equal(!!value, true, message)
.
If value
is not truthy, an AssertionError
is thrown with a message
property set equal to the value of the message
parameter. If the message
parameter is undefined
, a default error message is assigned.
const assert = require('assert');
assert.ok(true);
// OK
assert.ok(1);
// OK
assert.ok(false);
// throws "AssertionError: false == true"
assert.ok(0);
// throws "AssertionError: 0 == true"
assert.ok(false, 'it\'s false');
// throws "AssertionError: it's false"
assert.strictEqual(actual, expected[, message])#
actual
<any>expected
<any>message
<any>
Tests strict equality as determined by the Strict Equality Comparison
( ===
).
const assert = require('assert');
assert.strictEqual(1, 2);
// AssertionError: 1 === 2
assert.strictEqual(1, 1);
// OK
assert.strictEqual(1, '1');
// AssertionError: 1 === '1'
If the values are not strictly equal, an AssertionError
is thrown with a
message
property set equal to the value of the message
parameter. If the
message
parameter is undefined, a default error message is assigned.
assert.throws(block[, error][, message])#
block
<Function>error
<RegExp> | <Function>message
<any>
Expects the function block
to throw an error.
If specified, error
can be a constructor, RegExp
, or validation
function.
If specified, message
will be the message provided by the AssertionError
if
the block fails to throw.
Validate instanceof using constructor:
assert.throws(
() => {
throw new Error('Wrong value');
},
Error
);
Validate error message using RegExp
:
assert.throws(
() => {
throw new Error('Wrong value');
},
/value/
);
Custom error validation:
assert.throws(
() => {
throw new Error('Wrong value');
},
function(err) {
if ((err instanceof Error) && /value/.test(err)) {
return true;
}
},
'unexpected error'
);
Note that error
can not be a string. If a string is provided as the second
argument, then error
is assumed to be omitted and the string will be used for
message
instead. This can lead to easy-to-miss mistakes:
// THIS IS A MISTAKE! DO NOT DO THIS!
assert.throws(myFunction, 'missing foo', 'did not throw with expected message');
// Do this instead.
assert.throws(myFunction, /missing foo/, 'did not throw with expected message');
Caveats#
For the following cases, consider using ES2015 Object.is()
,
which uses the SameValueZero comparison.
const a = 0;
const b = -a;
assert.notStrictEqual(a, b);
// AssertionError: 0 !== -0
// Strict Equality Comparison doesn't distinguish between -0 and +0...
assert(!Object.is(a, b));
// but Object.is() does!
const str1 = 'foo';
const str2 = 'foo';
assert.strictEqual(str1 / 1, str2 / 1);
// AssertionError: NaN === NaN
// Strict Equality Comparison can't be used to check NaN...
assert(Object.is(str1 / 1, str2 / 1));
// but Object.is() can!
For more information, see MDN's guide on equality comparisons and sameness.
Async Hooks#
Stability: 1 - Experimental
The async_hooks
module provides an API to register callbacks tracking the
lifetime of asynchronous resources created inside a Node.js application.
It can be accessed using:
const async_hooks = require('async_hooks');
Terminology#
An asynchronous resource represents an object with an associated callback.
This callback may be called multiple times, for example, the connection
event
in net.createServer
, or just a single time like in fs.open
. A resource
can also be closed before the callback is called. AsyncHook does not
explicitly distinguish between these different cases but will represent them
as the abstract concept that is a resource.
Public API#
Overview#
Following is a simple overview of the public API.
const async_hooks = require('async_hooks');
// Return the ID of the current execution context.
const eid = async_hooks.executionAsyncId();
// Return the ID of the handle responsible for triggering the callback of the
// current execution scope to call.
const tid = async_hooks.triggerAsyncId();
// Create a new AsyncHook instance. All of these callbacks are optional.
const asyncHook = async_hooks.createHook({ init, before, after, destroy });
// Allow callbacks of this AsyncHook instance to call. This is not an implicit
// action after running the constructor, and must be explicitly run to begin
// executing callbacks.
asyncHook.enable();
// Disable listening for new asynchronous events.
asyncHook.disable();
//
// The following are the callbacks that can be passed to createHook().
//
// init is called during object construction. The resource may not have
// completed construction when this callback runs, therefore all fields of the
// resource referenced by "asyncId" may not have been populated.
function init(asyncId, type, triggerAsyncId, resource) { }
// before is called just before the resource's callback is called. It can be
// called 0-N times for handles (e.g. TCPWrap), and will be called exactly 1
// time for requests (e.g. FSReqWrap).
function before(asyncId) { }
// after is called just after the resource's callback has finished.
function after(asyncId) { }
// destroy is called when an AsyncWrap instance is destroyed.
function destroy(asyncId) { }
async_hooks.createHook(callbacks)
#
callbacks
<Object> the callbacks to register- Returns:
{AsyncHook}
instance used for disabling and enabling hooks
Registers functions to be called for different lifetime events of each async operation.
The callbacks init()
/before()
/after()
/destroy()
are called for the
respective asynchronous event during a resource's lifetime.
All callbacks are optional. So, for example, if only resource cleanup needs to
be tracked then only the destroy
callback needs to be passed. The
specifics of all functions that can be passed to callbacks
is in the section
Hook Callbacks
.
Error Handling#
If any AsyncHook
callbacks throw, the application will print the stack trace
and exit. The exit path does follow that of an uncaught exception but
all uncaughtException
listeners are removed, thus forcing the process to
exit. The 'exit'
callbacks will still be called unless the application is run
with --abort-on-uncaught-exception
, in which case a stack trace will be
printed and the application exits, leaving a core file.
The reason for this error handling behavior is that these callbacks are running at potentially volatile points in an object's lifetime, for example during class construction and destruction. Because of this, it is deemed necessary to bring down the process quickly in order to prevent an unintentional abort in the future. This is subject to change in the future if a comprehensive analysis is performed to ensure an exception can follow the normal control flow without unintentional side effects.
Printing in AsyncHooks callbacks#
Because printing to the console is an asynchronous operation, console.log()
will cause the AsyncHooks callbacks to be called. Using console.log()
or
similar asynchronous operations inside an AsyncHooks callback function will thus
cause an infinite recursion. An easily solution to this when debugging is
to use a synchronous logging operation such as fs.writeSync(1, msg)
. This
will print to stdout because 1
is the file descriptor for stdout and will
not invoke AsyncHooks recursively because it is synchronous.
const fs = require('fs');
const util = require('util');
function debug(...args) {
// use a function like this one when debugging inside an AsyncHooks callback
fs.writeSync(1, `${util.format(...args)}\n`);
}
If an asynchronous operation is needed for logging, it is possible to keep track of what caused the asynchronous operation using the information provided by AsyncHooks itself. The logging should then be skipped when it was the logging itself that caused AsyncHooks callback to call. By doing this the otherwise infinite recursion is broken.
asyncHook.enable()
#
- Returns <AsyncHook> A reference to
asyncHook
.
Enable the callbacks for a given AsyncHook
instance. If no callbacks are
provided enabling is a noop.
The AsyncHook
instance is by default disabled. If the AsyncHook
instance
should be enabled immediately after creation, the following pattern can be used.
const async_hooks = require('async_hooks');
const hook = async_hooks.createHook(callbacks).enable();
asyncHook.disable()
#
- Returns <AsyncHook> A reference to
asyncHook
.
Disable the callbacks for a given AsyncHook
instance from the global pool of
AsyncHook callbacks to be executed. Once a hook has been disabled it will not
be called again until enabled.
For API consistency disable()
also returns the AsyncHook
instance.
Hook Callbacks#
Key events in the lifetime of asynchronous events have been categorized into four areas: instantiation, before/after the callback is called, and when the instance is destructed.
init(asyncId, type, triggerAsyncId, resource)
#
asyncId
<number> a unique ID for the async resourcetype
<string> the type of the async resourcetriggerAsyncId
<number> the unique ID of the async resource in whose execution context this async resource was createdresource
<Object> reference to the resource representing the async operation, needs to be released during destroy
Called when a class is constructed that has the possibility to emit an
asynchronous event. This does not mean the instance must call
before
/after
before destroy
is called, only that the possibility
exists.
This behavior can be observed by doing something like opening a resource then closing it before the resource can be used. The following snippet demonstrates this.
require('net').createServer().listen(function() { this.close(); });
// OR
clearTimeout(setTimeout(() => {}, 10));
Every new resource is assigned a unique ID.
type
#
The type
is a string that represents the type of resource that caused
init
to be called. Generally, it will correspond to the name of the
resource's constructor.
FSEVENTWRAP, FSREQWRAP, GETADDRINFOREQWRAP, GETNAMEINFOREQWRAP, HTTPPARSER,
JSSTREAM, PIPECONNECTWRAP, PIPEWRAP, PROCESSWRAP, QUERYWRAP, SHUTDOWNWRAP,
SIGNALWRAP, STATWATCHER, TCPCONNECTWRAP, TCPWRAP, TIMERWRAP, TTYWRAP,
UDPSENDWRAP, UDPWRAP, WRITEWRAP, ZLIB, SSLCONNECTION, PBKDF2REQUEST,
RANDOMBYTESREQUEST, TLSWRAP, Timeout, Immediate, TickObject
There is also the PROMISE
resource type, which is used to track Promise
instances and asynchronous work scheduled by them.
Users are be able to define their own type
when using the public embedder API.
Note: It is possible to have type name collisions. Embedders are encouraged to use a unique prefixes, such as the npm package name, to prevent collisions when listening to the hooks.
triggerId
#
triggerAsyncId
is the asyncId
of the resource that caused (or "triggered") the
new resource to initialize and that caused init
to call. This is different
from async_hooks.executionAsyncId()
that only shows when a resource was
created, while triggerAsyncId
shows why a resource was created.
The following is a simple demonstration of triggerAsyncId
:
async_hooks.createHook({
init(asyncId, type, triggerAsyncId) {
const eid = async_hooks.executionAsyncId();
fs.writeSync(
1, `${type}(${asyncId}): trigger: ${triggerAsyncId} execution: ${eid}\n`);
}
}).enable();
require('net').createServer((conn) => {}).listen(8080);
Output when hitting the server with nc localhost 8080
:
TCPWRAP(2): trigger: 1 execution: 1
TCPWRAP(4): trigger: 2 execution: 0
The first TCPWRAP
is the server which receives the connections.
The second TCPWRAP
is the new connection from the client. When a new
connection is made the TCPWrap
instance is immediately constructed. This
happens outside of any JavaScript stack (side note: a executionAsyncId()
of 0
means it's being executed from C++, with no JavaScript stack above it).
With only that information it would be impossible to link resources together in
terms of what caused them to be created, so triggerAsyncId
is given the task of
propagating what resource is responsible for the new resource's existence.
resource
#
resource
is an object that represents the actual resource. This can contain
useful information such as the hostname for the GETADDRINFOREQWRAP
resource
type, which will be used when looking up the ip for the hostname in
net.Server.listen
. The API for getting this information is currently not
considered public, but using the Embedder API users can provide and document
their own resource objects. Such as resource object could for example contain
the SQL query being executed.
In the case of Promises, the resource
object will have promise
property
that refers to the Promise that is being initialized, and a parentId
property
that equals the asyncId
of a parent Promise, if there is one, and
undefined
otherwise. For example, in the case of b = a.then(handler)
,
a
is considered a parent Promise of b
.
Note: In some cases the resource object is reused for performance reasons,
it is thus not safe to use it as a key in a WeakMap
or add properties to it.
asynchronous context example#
Below is another example with additional information about the calls to
init
between the before
and after
calls, specifically what the
callback to listen()
will look like. The output formatting is slightly more
elaborate to make calling context easier to see.
let indent = 0;
async_hooks.createHook({
init(asyncId, type, triggerAsyncId) {
const eid = async_hooks.executionAsyncId();
const indentStr = ' '.repeat(indent);
fs.writeSync(
1,
`${indentStr}${type}(${asyncId}):` +
` trigger: ${triggerAsyncId} execution: ${eid}\n`);
},
before(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(1, `${indentStr}before: ${asyncId}\n`);
indent += 2;
},
after(asyncId) {
indent -= 2;
const indentStr = ' '.repeat(indent);
fs.writeSync(1, `${indentStr}after: ${asyncId}\n`);
},
destroy(asyncId) {
const indentStr = ' '.repeat(indent);
fs.writeSync(1, `${indentStr}destroy: ${asyncId}\n`);
},
}).enable();
require('net').createServer(() => {}).listen(8080, () => {
// Let's wait 10ms before logging the server started.
setTimeout(() => {
console.log('>>>', async_hooks.executionAsyncId());
}, 10);
});
Output from only starting the server:
TCPWRAP(2): trigger: 1 execution: 1
TickObject(3): trigger: 2 execution: 1
before: 3
Timeout(4): trigger: 3 execution: 3
TIMERWRAP(5): trigger: 3 execution: 3
after: 3
destroy: 3
before: 5
before: 4
TTYWRAP(6): trigger: 4 execution: 4
SIGNALWRAP(7): trigger: 4 execution: 4
TTYWRAP(8): trigger: 4 execution: 4
>>> 4
TickObject(9): trigger: 4 execution: 4
after: 4
after: 5
before: 9
after: 9
destroy: 4
destroy: 9
destroy: 5
Note: As illustrated in the example, executionAsyncId()
and execution
each specify the value of the current execution context; which is delineated by
calls to before
and after
.
Only using execution
to graph resource allocation results in the following:
TTYWRAP(6) -> Timeout(4) -> TIMERWRAP(5) -> TickObject(3) -> root(1)
The TCPWRAP
isn't part of this graph; even though it was the reason for
console.log()
being called. This is because binding to a port without a
hostname is actually synchronous, but to maintain a completely asynchronous API
the user's callback is placed in a process.nextTick()
.
The graph only shows when a resource was created, not why, so to track
the why use triggerAsyncId
.
before(asyncId)
#
asyncId
<number>
When an asynchronous operation is initiated (such as a TCP server receiving a
new connection) or completes (such as writing data to disk) a callback is
called to notify the user. The before
callback is called just before said
callback is executed. asyncId
is the unique identifier assigned to the
resource about to execute the callback.
The before
callback will be called 0 to N times. The before
callback
will typically be called 0 times if the asynchronous operation was cancelled
or for example if no connections are received by a TCP server. Asynchronous
like the TCP server will typically call the before
callback multiple times,
while other operations like fs.open()
will only call it once.
after(asyncId)
#
asyncId
<number>
Called immediately after the callback specified in before
is completed.
Note: If an uncaught exception occurs during execution of the callback then
after
will run after the 'uncaughtException'
event is emitted or a
domain
's handler runs.
destroy(asyncId)
#
asyncId
<number>
Called after the resource corresponding to asyncId
is destroyed. It is also called
asynchronously from the embedder API emitDestroy()
.
Note: Some resources depend on GC for cleanup, so if a reference is made to
the resource
object passed to init
it's possible that destroy
is
never called, causing a memory leak in the application. Of course if
the resource doesn't depend on GC then this isn't an issue.
async_hooks.executionAsyncId()
#
- Returns <number> the
asyncId
of the current execution context. Useful to track when something calls.
For example:
console.log(async_hooks.executionAsyncId()); // 1 - bootstrap
fs.open(path, 'r', (err, fd) => {
console.log(async_hooks.executionAsyncId()); // 6 - open()
});
It is important to note that the ID returned fom executionAsyncId()
is related
to execution timing, not causality (which is covered by triggerAsyncId()
). For
example:
const server = net.createServer(function onConnection(conn) {
// Returns the ID of the server, not of the new connection, because the
// onConnection callback runs in the execution scope of the server's
// MakeCallback().
async_hooks.executionAsyncId();
}).listen(port, function onListening() {
// Returns the ID of a TickObject (i.e. process.nextTick()) because all
// callbacks passed to .listen() are wrapped in a nextTick().
async_hooks.executionAsyncId();
});
async_hooks.triggerAsyncId()
#
- Returns <number> the ID of the resource responsible for calling the callback that is currently being executed.
For example:
const server = net.createServer((conn) => {
// The resource that caused (or triggered) this callback to be called
// was that of the new connection. Thus the return value of triggerAsyncId()
// is the asyncId of "conn".
async_hooks.triggerAsyncId();
}).listen(port, () => {
// Even though all callbacks passed to .listen() are wrapped in a nextTick()
// the callback itself exists because the call to the server's .listen()
// was made. So the return value would be the ID of the server.
async_hooks.triggerAsyncId();
});
JavaScript Embedder API#
Library developers that handle their own I/O, a connection pool, or callback queues will need to hook into the AsyncWrap API so that all the appropriate callbacks are called. To accommodate this a JavaScript API is provided.
class AsyncResource()
#
The class AsyncResource
was designed to be extended by the embedder's async
resources. Using this users can easily trigger the lifetime events of their
own resources.
The init
hook will trigger when an AsyncResource
is instantiated.
It is important that before
/after
calls are unwound
in the same order they are called. Otherwise an unrecoverable exception
will occur and node will abort.
The following is an overview of the AsyncResource
API.
const { AsyncResource } = require('async_hooks');
// AsyncResource() is meant to be extended. Instantiating a
// new AsyncResource() also triggers init. If triggerAsyncId is omitted then
// async_hook.executionAsyncId() is used.
const asyncResource = new AsyncResource(type, triggerAsyncId);
// Call AsyncHooks before callbacks.
asyncResource.emitBefore();
// Call AsyncHooks after callbacks.
asyncResource.emitAfter();
// Call AsyncHooks destroy callbacks.
asyncResource.emitDestroy();
// Return the unique ID assigned to the AsyncResource instance.
asyncResource.asyncId();
// Return the trigger ID for the AsyncResource instance.
asyncResource.triggerAsyncId();
AsyncResource(type[, triggerAsyncId])
#
Example usage:
class DBQuery extends AsyncResource {
constructor(db) {
super('DBQuery');
this.db = db;
}
getInfo(query, callback) {
this.db.get(query, (err, data) => {
this.emitBefore();
callback(err, data);
this.emitAfter();
});
}
close() {
this.db = null;
this.emitDestroy();
}
}
asyncResource.emitBefore()
#
- Returns <undefined>
Call all before
callbacks and let them know a new asynchronous execution
context is being entered. If nested calls to emitBefore()
are made, the stack
of asyncId
s will be tracked and properly unwound.
asyncResource.emitAfter()
#
- Returns <undefined>
Call all after
callbacks. If nested calls to emitBefore()
were made, then
make sure the stack is unwound properly. Otherwise an error will be thrown.
If the user's callback throws an exception then emitAfter()
will
automatically be called for all asyncId
s on the stack if the error is handled by
a domain or 'uncaughtException'
handler.
asyncResource.emitDestroy()
#
- Returns <undefined>
Call all destroy
hooks. This should only ever be called once. An error will
be thrown if it is called more than once. This must be manually called. If
the resource is left to be collected by the GC then the destroy
hooks will
never be called.
asyncResource.asyncId()
#
- Returns <number> the unique
asyncId
assigned to the resource.
asyncResource.triggerAsyncId()
#
- Returns <number> the same
triggerAsyncId
that is passed to theAsyncResource
constructor.
Buffer#
Stability: 2 - Stable
Prior to the introduction of TypedArray
in ECMAScript 2015 (ES6), the
JavaScript language had no mechanism for reading or manipulating streams
of binary data. The Buffer
class was introduced as part of the Node.js
API to make it possible to interact with octet streams in the context of things
like TCP streams and file system operations.
Now that TypedArray
has been added in ES6, the Buffer
class implements the
Uint8Array
API in a manner that is more optimized and suitable for Node.js'
use cases.
Instances of the Buffer
class are similar to arrays of integers but
correspond to fixed-sized, raw memory allocations outside the V8 heap.
The size of the Buffer
is established when it is created and cannot be
resized.
The Buffer
class is a global within Node.js, making it unlikely that one
would need to ever use require('buffer').Buffer
.
Examples:
// Creates a zero-filled Buffer of length 10.
const buf1 = Buffer.alloc(10);
// Creates a Buffer of length 10, filled with 0x1.
const buf2 = Buffer.alloc(10, 1);
// Creates an uninitialized buffer of length 10.
// This is faster than calling Buffer.alloc() but the returned
// Buffer instance might contain old data that needs to be
// overwritten using either fill() or write().
const buf3 = Buffer.allocUnsafe(10);
// Creates a Buffer containing [0x1, 0x2, 0x3].
const buf4 = Buffer.from([1, 2, 3]);
// Creates a Buffer containing UTF-8 bytes [0x74, 0xc3, 0xa9, 0x73, 0x74].
const buf5 = Buffer.from('tést');
// Creates a Buffer containing Latin-1 bytes [0x74, 0xe9, 0x73, 0x74].
const buf6 = Buffer.from('tést', 'latin1');
Buffer.from()
, Buffer.alloc()
, and Buffer.allocUnsafe()
#
In versions of Node.js prior to v6, Buffer
instances were created using the
Buffer
constructor function, which allocates the returned Buffer
differently based on what arguments are provided:
- Passing a number as the first argument to
Buffer()
(e.g.new Buffer(10)
), allocates a newBuffer
object of the specified size. Prior to Node.js 8.0.0, the memory allocated for suchBuffer
instances is not initialized and can contain sensitive data. SuchBuffer
instances must be subsequently initialized by using eitherbuf.fill(0)
or by writing to theBuffer
completely. While this behavior is intentional to improve performance, development experience has demonstrated that a more explicit distinction is required between creating a fast-but-uninitializedBuffer
versus creating a slower-but-saferBuffer
. Starting in Node.js 8.0.0,Buffer(num)
andnew Buffer(num)
will return aBuffer
with initialized memory. - Passing a string, array, or
Buffer
as the first argument copies the passed object's data into theBuffer
. - Passing an
ArrayBuffer
returns aBuffer
that shares allocated memory with the givenArrayBuffer
.
Because the behavior of new Buffer()
changes significantly based on the type
of value passed as the first argument, applications that do not properly
validate the input arguments passed to new Buffer()
, or that fail to
appropriately initialize newly allocated Buffer
content, can inadvertently
introduce security and reliability issues into their code.
To make the creation of Buffer
instances more reliable and less error prone,
the various forms of the new Buffer()
constructor have been deprecated
and replaced by separate Buffer.from()
, Buffer.alloc()
, and
Buffer.allocUnsafe()
methods.
Developers should migrate all existing uses of the new Buffer()
constructors
to one of these new APIs.
Buffer.from(array)
returns a newBuffer
containing a copy of the provided octets.Buffer.from(arrayBuffer[, byteOffset [, length]])
returns a newBuffer
that shares the same allocated memory as the givenArrayBuffer
.Buffer.from(buffer)
returns a newBuffer
containing a copy of the contents of the givenBuffer
.Buffer.from(string[, encoding])
returns a newBuffer
containing a copy of the provided string.Buffer.alloc(size[, fill[, encoding]])
returns a "filled"Buffer
instance of the specified size. This method can be significantly slower thanBuffer.allocUnsafe(size)
but ensures that newly createdBuffer
instances never contain old and potentially sensitive data.Buffer.allocUnsafe(size)
andBuffer.allocUnsafeSlow(size)
each return a newBuffer
of the specifiedsize
whose content must be initialized using eitherbuf.fill(0)
or written to completely.
Buffer
instances returned by Buffer.allocUnsafe()
may be allocated off
a shared internal memory pool if size
is less than or equal to half
Buffer.poolSize
. Instances returned by Buffer.allocUnsafeSlow()
never
use the shared internal memory pool.
The --zero-fill-buffers
command line option#
Node.js can be started using the --zero-fill-buffers
command line option to
force all newly allocated Buffer
instances created using either
new Buffer(size)
, Buffer.allocUnsafe()
, Buffer.allocUnsafeSlow()
or
new SlowBuffer(size)
to be automatically zero-filled upon creation. Use of
this flag changes the default behavior of these methods and can have a significant
impact on performance. Use of the --zero-fill-buffers
option is recommended
only when necessary to enforce that newly allocated Buffer
instances cannot
contain potentially sensitive data.
Example:
$ node --zero-fill-buffers
> Buffer.allocUnsafe(5);
<Buffer 00 00 00 00 00>
What makes Buffer.allocUnsafe()
and Buffer.allocUnsafeSlow()
"unsafe"?#
When calling Buffer.allocUnsafe()
and Buffer.allocUnsafeSlow()
, the
segment of allocated memory is uninitialized (it is not zeroed-out). While
this design makes the allocation of memory quite fast, the allocated segment of
memory might contain old data that is potentially sensitive. Using a Buffer
created by Buffer.allocUnsafe()
without completely overwriting the memory
can allow this old data to be leaked when the Buffer
memory is read.
While there are clear performance advantages to using Buffer.allocUnsafe()
,
extra care must be taken in order to avoid introducing security
vulnerabilities into an application.
Buffers and Character Encodings#
Buffer
instances are commonly used to represent sequences of encoded characters
such as UTF-8, UCS2, Base64 or even Hex-encoded data. It is possible to
convert back and forth between Buffer
instances and ordinary JavaScript strings
by using an explicit character encoding.
Example:
const buf = Buffer.from('hello world', 'ascii');
// Prints: 68656c6c6f20776f726c64
console.log(buf.toString('hex'));
// Prints: aGVsbG8gd29ybGQ=
console.log(buf.toString('base64'));
The character encodings currently supported by Node.js include:
'ascii'
- for 7-bit ASCII data only. This encoding is fast and will strip the high bit if set.'utf8'
- Multibyte encoded Unicode characters. Many web pages and other document formats use UTF-8.'utf16le'
- 2 or 4 bytes, little-endian encoded Unicode characters. Surrogate pairs (U+10000 to U+10FFFF) are supported.'ucs2'
- Alias of'utf16le'
.'base64'
- Base64 encoding. When creating aBuffer
from a string, this encoding will also correctly accept "URL and Filename Safe Alphabet" as specified in RFC4648, Section 5.'latin1'
- A way of encoding theBuffer
into a one-byte encoded string (as defined by the IANA in RFC1345, page 63, to be the Latin-1 supplement block and C0/C1 control codes).'binary'
- Alias for'latin1'
.'hex'
- Encode each byte as two hexadecimal characters.
Note: Today's browsers follow the WHATWG spec which aliases both 'latin1'
and ISO-8859-1 to win-1252. This means that while doing something like
http.get()
, if the returned charset is one of those listed in the WHATWG spec
it's possible that the server actually returned win-1252-encoded data, and
using 'latin1'
encoding may incorrectly decode the characters.
Buffers and TypedArray#
Buffer
instances are also Uint8Array
instances. However, there are subtle
incompatibilities with the TypedArray specification in ECMAScript 2015.
For example, while ArrayBuffer#slice()
creates a copy of the slice, the
implementation of Buffer#slice()
creates a view over the
existing Buffer
without copying, making Buffer#slice()
far
more efficient.
It is also possible to create new TypedArray
instances from a Buffer
with
the following caveats:
The
Buffer
object's memory is copied to theTypedArray
, not shared.The
Buffer
object's memory is interpreted as an array of distinct elements, and not as a byte array of the target type. That is,new Uint32Array(Buffer.from([1, 2, 3, 4]))
creates a 4-elementUint32Array
with elements[1, 2, 3, 4]
, not aUint32Array
with a single element[0x1020304]
or[0x4030201]
.
It is possible to create a new Buffer
that shares the same allocated memory as
a TypedArray
instance by using the TypeArray object's .buffer
property.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Copies the contents of `arr`
const buf1 = Buffer.from(arr);
// Shares memory with `arr`
const buf2 = Buffer.from(arr.buffer);
// Prints: <Buffer 88 a0>
console.log(buf1);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf2);
arr[1] = 6000;
// Prints: <Buffer 88 a0>
console.log(buf1);
// Prints: <Buffer 88 13 70 17>
console.log(buf2);
Note that when creating a Buffer
using a TypedArray
's .buffer
, it is
possible to use only a portion of the underlying ArrayBuffer
by passing in
byteOffset
and length
parameters.
Example:
const arr = new Uint16Array(20);
const buf = Buffer.from(arr.buffer, 0, 16);
// Prints: 16
console.log(buf.length);
The Buffer.from()
and TypedArray.from()
have different signatures and
implementations. Specifically, the TypedArray
variants accept a second
argument that is a mapping function that is invoked on every element of the
typed array:
TypedArray.from(source[, mapFn[, thisArg]])
The Buffer.from()
method, however, does not support the use of a mapping
function:
Buffer.from(array)
Buffer.from(buffer)
Buffer.from(arrayBuffer[, byteOffset [, length]])
Buffer.from(string[, encoding])
Buffers and ES6 iteration#
Buffer
instances can be iterated over using the ECMAScript 2015 (ES6) for..of
syntax.
Example:
const buf = Buffer.from([1, 2, 3]);
// Prints:
// 1
// 2
// 3
for (const b of buf) {
console.log(b);
}
Additionally, the buf.values()
, buf.keys()
, and
buf.entries()
methods can be used to create iterators.
Class: Buffer#
The Buffer
class is a global type for dealing with binary data directly.
It can be constructed in a variety of ways.
new Buffer(array)#
Stability: 0 - Deprecated: Use Buffer.from(array)
instead.
array
<Array> An array of bytes to copy from
Allocates a new Buffer
using an array
of octets.
Example:
// Creates a new Buffer containing the UTF-8 bytes of the string 'buffer'
const buf = new Buffer([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
new Buffer(arrayBuffer[, byteOffset [, length]])#
Stability: 0 - Deprecated: Use Buffer.from(arrayBuffer[, byteOffset [, length]])
instead.
arrayBuffer
<ArrayBuffer> AnArrayBuffer
or the.buffer
property of aTypedArray
.byteOffset
<integer> Index of first byte to expose. Default:0
length
<integer> Number of bytes to expose. Default:arrayBuffer.length - byteOffset
This creates a view of the ArrayBuffer
without copying the underlying
memory. For example, when passed a reference to the .buffer
property of a
TypedArray
instance, the newly created Buffer
will share the same
allocated memory as the TypedArray
.
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`
const buf = new Buffer(arr.buffer);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf);
// Changing the original Uint16Array changes the Buffer also
arr[1] = 6000;
// Prints: <Buffer 88 13 70 17>
console.log(buf);
new Buffer(buffer)#
Stability: 0 - Deprecated: Use Buffer.from(buffer)
instead.
buffer
<Buffer> An existingBuffer
to copy data from
Copies the passed buffer
data onto a new Buffer
instance.
Example:
const buf1 = new Buffer('buffer');
const buf2 = new Buffer(buf1);
buf1[0] = 0x61;
// Prints: auffer
console.log(buf1.toString());
// Prints: buffer
console.log(buf2.toString());
new Buffer(size)#
Stability: 0 - Deprecated: UseBuffer.alloc()
instead (also seeBuffer.allocUnsafe()
).
size
<integer> The desired length of the newBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, a RangeError
will be
thrown. A zero-length Buffer
will be created if size
is 0.
Prior to Node.js 8.0.0, the underlying memory for Buffer
instances
created in this way is not initialized. The contents of a newly created
Buffer
are unknown and may contain sensitive data. Use
Buffer.alloc(size)
instead to initialize a Buffer
to zeroes.
Example:
const buf = new Buffer(10);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
new Buffer(string[, encoding])#
Stability: 0 - Deprecated: Use Buffer.from(string[, encoding])
instead.
Creates a new Buffer
containing the given JavaScript string string
. If
provided, the encoding
parameter identifies the character encoding of string
.
Examples:
const buf1 = new Buffer('this is a tést');
// Prints: this is a tést
console.log(buf1.toString());
// Prints: this is a tC)st
console.log(buf1.toString('ascii'));
const buf2 = new Buffer('7468697320697320612074c3a97374', 'hex');
// Prints: this is a tést
console.log(buf2.toString());
Class Method: Buffer.alloc(size[, fill[, encoding]])#
size
<integer> The desired length of the newBuffer
fill
<string> | <Buffer> | <integer> A value to pre-fill the newBuffer
with. Default:0
encoding
<string> Iffill
is a string, this is its encoding. Default:'utf8'
Allocates a new Buffer
of size
bytes. If fill
is undefined
, the
Buffer
will be zero-filled.
Example:
const buf = Buffer.alloc(5);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, a RangeError
will be
thrown. A zero-length Buffer
will be created if size
is 0.
If fill
is specified, the allocated Buffer
will be initialized by calling
buf.fill(fill)
.
Example:
const buf = Buffer.alloc(5, 'a');
// Prints: <Buffer 61 61 61 61 61>
console.log(buf);
If both fill
and encoding
are specified, the allocated Buffer
will be
initialized by calling buf.fill(fill, encoding)
.
Example:
const buf = Buffer.alloc(11, 'aGVsbG8gd29ybGQ=', 'base64');
// Prints: <Buffer 68 65 6c 6c 6f 20 77 6f 72 6c 64>
console.log(buf);
Calling Buffer.alloc()
can be significantly slower than the alternative
Buffer.allocUnsafe()
but ensures that the newly created Buffer
instance
contents will never contain sensitive data.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.allocUnsafe(size)#
size
<integer> The desired length of the newBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, a RangeError
will be
thrown. A zero-length Buffer
will be created if size
is 0.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use Buffer.alloc()
instead to initialize
Buffer
instances to zeroes.
Example:
const buf = Buffer.allocUnsafe(10);
// Prints: (contents may vary): <Buffer a0 8b 28 3f 01 00 00 00 50 32>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00 00 00 00 00 00>
console.log(buf);
A TypeError
will be thrown if size
is not a number.
Note that the Buffer
module pre-allocates an internal Buffer
instance of
size Buffer.poolSize
that is used as a pool for the fast allocation of new
Buffer
instances created using Buffer.allocUnsafe()
and the deprecated
new Buffer(size)
constructor only when size
is less than or equal to
Buffer.poolSize >> 1
(floor of Buffer.poolSize
divided by two).
Use of this pre-allocated internal memory pool is a key difference between
calling Buffer.alloc(size, fill)
vs. Buffer.allocUnsafe(size).fill(fill)
.
Specifically, Buffer.alloc(size, fill)
will never use the internal Buffer
pool, while Buffer.allocUnsafe(size).fill(fill)
will use the internal
Buffer
pool if size
is less than or equal to half Buffer.poolSize
. The
difference is subtle but can be important when an application requires the
additional performance that Buffer.allocUnsafe()
provides.
Class Method: Buffer.allocUnsafeSlow(size)#
size
<integer> The desired length of the newBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, a RangeError
will be
thrown. A zero-length Buffer
will be created if size
is 0.
The underlying memory for Buffer
instances created in this way is not
initialized. The contents of the newly created Buffer
are unknown and
may contain sensitive data. Use buf.fill(0)
to initialize such
Buffer
instances to zeroes.
When using Buffer.allocUnsafe()
to allocate new Buffer
instances,
allocations under 4KB are, by default, sliced from a single pre-allocated
Buffer
. This allows applications to avoid the garbage collection overhead of
creating many individually allocated Buffer
instances. This approach improves
both performance and memory usage by eliminating the need to track and cleanup as
many Persistent
objects.
However, in the case where a developer may need to retain a small chunk of
memory from a pool for an indeterminate amount of time, it may be appropriate
to create an un-pooled Buffer
instance using Buffer.allocUnsafeSlow()
then
copy out the relevant bits.
Example:
// Need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// Allocate for retained data
const sb = Buffer.allocUnsafeSlow(10);
// Copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of Buffer.allocUnsafeSlow()
should be used only as a last resort after
a developer has observed undue memory retention in their applications.
A TypeError
will be thrown if size
is not a number.
Class Method: Buffer.byteLength(string[, encoding])#
string
<string> | <Buffer> | <TypedArray> | <DataView> | <ArrayBuffer> A value to calculate the length ofencoding
<string> Ifstring
is a string, this is its encoding. Default:'utf8'
- Returns: <integer> The number of bytes contained within
string
Returns the actual byte length of a string. This is not the same as
String.prototype.length
since that returns the number of characters in
a string.
Note: For 'base64'
and 'hex'
, this function assumes valid input. For
strings that contain non-Base64/Hex-encoded data (e.g. whitespace), the return
value might be greater than the length of a Buffer
created from the string.
Example:
const str = '\u00bd + \u00bc = \u00be';
// Prints: ½ + ¼ = ¾: 9 characters, 12 bytes
console.log(`${str}: ${str.length} characters, ` +
`${Buffer.byteLength(str, 'utf8')} bytes`);
When string
is a Buffer
/DataView
/TypedArray
/ArrayBuffer
, the
actual byte length is returned.
Class Method: Buffer.compare(buf1, buf2)#
buf1
<Buffer> | <Uint8Array>buf2
<Buffer> | <Uint8Array>- Returns: <integer>
Compares buf1
to buf2
typically for the purpose of sorting arrays of
Buffer
instances. This is equivalent to calling
buf1.compare(buf2)
.
Example:
const buf1 = Buffer.from('1234');
const buf2 = Buffer.from('0123');
const arr = [buf1, buf2];
// Prints: [ <Buffer 30 31 32 33>, <Buffer 31 32 33 34> ]
// (This result is equal to: [buf2, buf1])
console.log(arr.sort(Buffer.compare));
Class Method: Buffer.concat(list[, totalLength])#
list
<Array> List ofBuffer
orUint8Array
instances to concattotalLength
<integer> Total length of theBuffer
instances inlist
when concatenated- Returns: <Buffer>
Returns a new Buffer
which is the result of concatenating all the Buffer
instances in the list
together.
If the list has no items, or if the totalLength
is 0, then a new zero-length
Buffer
is returned.
If totalLength
is not provided, it is calculated from the Buffer
instances
in list
. This however causes an additional loop to be executed in order to
calculate the totalLength
, so it is faster to provide the length explicitly if
it is already known.
If totalLength
is provided, it is coerced to an unsigned integer. If the
combined length of the Buffer
s in list
exceeds totalLength
, the result is
truncated to totalLength
.
Example: Create a single Buffer
from a list of three Buffer
instances
const buf1 = Buffer.alloc(10);
const buf2 = Buffer.alloc(14);
const buf3 = Buffer.alloc(18);
const totalLength = buf1.length + buf2.length + buf3.length;
// Prints: 42
console.log(totalLength);
const bufA = Buffer.concat([buf1, buf2, buf3], totalLength);
// Prints: <Buffer 00 00 00 00 ...>
console.log(bufA);
// Prints: 42
console.log(bufA.length);
Class Method: Buffer.from(array)#
array
<Array>
Allocates a new Buffer
using an array
of octets.
Example:
// Creates a new Buffer containing UTF-8 bytes of the string 'buffer'
const buf = Buffer.from([0x62, 0x75, 0x66, 0x66, 0x65, 0x72]);
A TypeError
will be thrown if array
is not an Array
.
Class Method: Buffer.from(arrayBuffer[, byteOffset[, length]])#
arrayBuffer
<ArrayBuffer> AnArrayBuffer
or the.buffer
property of aTypedArray
.byteOffset
<integer> Index of first byte to expose. Default:0
length
<integer> Number of bytes to expose. Default:arrayBuffer.length - byteOffset
This creates a view of the ArrayBuffer
without copying the underlying
memory. For example, when passed a reference to the .buffer
property of a
TypedArray
instance, the newly created Buffer
will share the same
allocated memory as the TypedArray
.
Example:
const arr = new Uint16Array(2);
arr[0] = 5000;
arr[1] = 4000;
// Shares memory with `arr`
const buf = Buffer.from(arr.buffer);
// Prints: <Buffer 88 13 a0 0f>
console.log(buf);
// Changing the original Uint16Array changes the Buffer also
arr[1] = 6000;
// Prints: <Buffer 88 13 70 17>
console.log(buf);
The optional byteOffset
and length
arguments specify a memory range within
the arrayBuffer
that will be shared by the Buffer
.
Example:
const ab = new ArrayBuffer(10);
const buf = Buffer.from(ab, 0, 2);
// Prints: 2
console.log(buf.length);
A TypeError
will be thrown if arrayBuffer
is not an ArrayBuffer
.
Class Method: Buffer.from(buffer)#
buffer
<Buffer> An existingBuffer
to copy data from
Copies the passed buffer
data onto a new Buffer
instance.
Example:
const buf1 = Buffer.from('buffer');
const buf2 = Buffer.from(buf1);
buf1[0] = 0x61;
// Prints: auffer
console.log(buf1.toString());
// Prints: buffer
console.log(buf2.toString());
A TypeError
will be thrown if buffer
is not a Buffer
.
Class Method: Buffer.from(string[, encoding])#
Creates a new Buffer
containing the given JavaScript string string
. If
provided, the encoding
parameter identifies the character encoding of string
.
Examples:
const buf1 = Buffer.from('this is a tést');
// Prints: this is a tést
console.log(buf1.toString());
// Prints: this is a tC)st
console.log(buf1.toString('ascii'));
const buf2 = Buffer.from('7468697320697320612074c3a97374', 'hex');
// Prints: this is a tést
console.log(buf2.toString());
A TypeError
will be thrown if str
is not a string.
Class Method: Buffer.from(object[, offsetOrEncoding[, length]])#
object
<Object> An object supportingSymbol.toPrimitive
orvalueOf()
offsetOrEncoding
<number> | <string> A byte-offset or encoding, depending on the value returned either byobject.valueOf()
orobject[Symbol.toPrimitive]()
.length
<number> A length, depending on the value returned either byobject.valueOf()
orobject[Symbol.toPrimitive]()
.
For objects whose valueOf()
function returns a value not strictly equal to
object
, returns Buffer.from(object.valueOf(), offsetOrEncoding, length)
.
For example:
const buf = Buffer.from(new String('this is a test'));
// <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
For objects that support Symbol.toPrimitive
, returns
Buffer.from(object[Symbol.toPrimitive](), offsetOrEncoding, length)
.
For example:
class Foo {
[Symbol.toPrimitive]() {
return 'this is a test';
}
}
const buf = Buffer.from(new Foo(), 'utf8');
// <Buffer 74 68 69 73 20 69 73 20 61 20 74 65 73 74>
Class Method: Buffer.isBuffer(obj)#
Returns true
if obj
is a Buffer
, false
otherwise.
Class Method: Buffer.isEncoding(encoding)#
Returns true
if encoding
contains a supported character encoding, or false
otherwise.
Class Property: Buffer.poolSize#
- <integer> Default:
8192
This is the number of bytes used to determine the size of pre-allocated, internal
Buffer
instances used for pooling. This value may be modified.
buf[index]#
The index operator [index]
can be used to get and set the octet at position
index
in buf
. The values refer to individual bytes, so the legal value
range is between 0x00
and 0xFF
(hex) or 0
and 255
(decimal).
This operator is inherited from Uint8Array
, so its behavior on out-of-bounds
access is the same as UInt8Array
- that is, getting returns undefined
and
setting does nothing.
Example: Copy an ASCII string into a Buffer
, one byte at a time
const str = 'Node.js';
const buf = Buffer.allocUnsafe(str.length);
for (let i = 0; i < str.length; i++) {
buf[i] = str.charCodeAt(i);
}
// Prints: Node.js
console.log(buf.toString('ascii'));
buf.buffer#
The buffer
property references the underlying ArrayBuffer
object based on
which this Buffer object is created.
const arrayBuffer = new ArrayBuffer(16);
const buffer = Buffer.from(arrayBuffer);
console.log(buffer.buffer === arrayBuffer);
// Prints: true
buf.compare(target[, targetStart[, targetEnd[, sourceStart[, sourceEnd]]]])#
target
<Buffer> | <Uint8Array> ABuffer
orUint8Array
to compare totargetStart
<integer> The offset withintarget
at which to begin comparison. Default:0
targetEnd
<integer> The offset withtarget
at which to end comparison (not inclusive). Ignored whentargetStart
isundefined
. Default:target.length
sourceStart
<integer> The offset withinbuf
at which to begin comparison. Ignored whentargetStart
isundefined
. Default:0
sourceEnd
<integer> The offset withinbuf
at which to end comparison (not inclusive). Ignored whentargetStart
isundefined
. Default:buf.length
- Returns: <integer>
Compares buf
with target
and returns a number indicating whether buf
comes before, after, or is the same as target
in sort order.
Comparison is based on the actual sequence of bytes in each Buffer
.
0
is returned iftarget
is the same asbuf
1
is returned iftarget
should come beforebuf
when sorted.-1
is returned iftarget
should come afterbuf
when sorted.
Examples:
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('BCD');
const buf3 = Buffer.from('ABCD');
// Prints: 0
console.log(buf1.compare(buf1));
// Prints: -1
console.log(buf1.compare(buf2));
// Prints: -1
console.log(buf1.compare(buf3));
// Prints: 1
console.log(buf2.compare(buf1));
// Prints: 1
console.log(buf2.compare(buf3));
// Prints: [ <Buffer 41 42 43>, <Buffer 41 42 43 44>, <Buffer 42 43 44> ]
// (This result is equal to: [buf1, buf3, buf2])
console.log([buf1, buf2, buf3].sort(Buffer.compare));
The optional targetStart
, targetEnd
, sourceStart
, and sourceEnd
arguments can be used to limit the comparison to specific ranges within target
and buf
respectively.
Examples:
const buf1 = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8, 9]);
const buf2 = Buffer.from([5, 6, 7, 8, 9, 1, 2, 3, 4]);
// Prints: 0
console.log(buf1.compare(buf2, 5, 9, 0, 4));
// Prints: -1
console.log(buf1.compare(buf2, 0, 6, 4));
// Prints: 1
console.log(buf1.compare(buf2, 5, 6, 5));
A RangeError
will be thrown if: targetStart < 0
, sourceStart < 0
,
targetEnd > target.byteLength
or sourceEnd > source.byteLength
.
buf.copy(target[, targetStart[, sourceStart[, sourceEnd]]])#
target
<Buffer> | <Uint8Array> ABuffer
orUint8Array
to copy into.targetStart
<integer> The offset withintarget
at which to begin copying to. Default:0
sourceStart
<integer> The offset withinbuf
at which to begin copying from. Ignored whentargetStart
isundefined
. Default:0
sourceEnd
<integer> The offset withinbuf
at which to stop copying (not inclusive). Ignored whensourceStart
isundefined
. Default:buf.length
- Returns: <integer> The number of bytes copied.
Copies data from a region of buf
to a region in target
even if the target
memory region overlaps with buf
.
Example: Create two Buffer
instances, buf1
and buf2
, and copy buf1
from
byte 16 through byte 19 into buf2
, starting at the 8th byte in buf2
const buf1 = Buffer.allocUnsafe(26);
const buf2 = Buffer.allocUnsafe(26).fill('!');
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
buf1.copy(buf2, 8, 16, 20);
// Prints: !!!!!!!!qrst!!!!!!!!!!!!!
console.log(buf2.toString('ascii', 0, 25));
Example: Create a single Buffer
and copy data from one region to an
overlapping region within the same Buffer
const buf = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf[i] = i + 97;
}
buf.copy(buf, 0, 4, 10);
// Prints: efghijghijklmnopqrstuvwxyz
console.log(buf.toString());
buf.entries()#
- Returns: <Iterator>
Creates and returns an iterator of [index, byte]
pairs from the contents of
buf
.
Example: Log the entire contents of a Buffer
const buf = Buffer.from('buffer');
// Prints:
// [0, 98]
// [1, 117]
// [2, 102]
// [3, 102]
// [4, 101]
// [5, 114]
for (const pair of buf.entries()) {
console.log(pair);
}
buf.equals(otherBuffer)#
otherBuffer
<Buffer> ABuffer
orUint8Array
to compare to- Returns: <boolean>
Returns true
if both buf
and otherBuffer
have exactly the same bytes,
false
otherwise.
Examples:
const buf1 = Buffer.from('ABC');
const buf2 = Buffer.from('414243', 'hex');
const buf3 = Buffer.from('ABCD');
// Prints: true
console.log(buf1.equals(buf2));
// Prints: false
console.log(buf1.equals(buf3));
buf.fill(value[, offset[, end]][, encoding])#
value
<string> | <Buffer> | <integer> The value to fillbuf
withoffset
<integer> Where to start fillingbuf
. Default:0
end
<integer> Where to stop fillingbuf
(not inclusive). Default:buf.length
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <Buffer> A reference to
buf
Fills buf
with the specified value
. If the offset
and end
are not given,
the entire buf
will be filled. This is meant to be a small simplification to
allow the creation and filling of a Buffer
to be done on a single line.
Example: Fill a Buffer
with the ASCII character 'h'
const b = Buffer.allocUnsafe(50).fill('h');
// Prints: hhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhhh
console.log(b.toString());
value
is coerced to a uint32
value if it is not a String or Integer.
If the final write of a fill()
operation falls on a multi-byte character,
then only the first bytes of that character that fit into buf
are written.
Example: Fill a Buffer
with a two-byte character
// Prints: <Buffer c8 a2 c8>
console.log(Buffer.allocUnsafe(3).fill('\u0222'));
buf.includes(value[, byteOffset][, encoding])#
value
<string> | <Buffer> | <integer> What to search forbyteOffset
<integer> Where to begin searching inbuf
. Default:0
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <boolean>
true
ifvalue
was found inbuf
,false
otherwise
Equivalent to buf.indexOf() !== -1
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: true
console.log(buf.includes('this'));
// Prints: true
console.log(buf.includes('is'));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer')));
// Prints: true
// (97 is the decimal ASCII value for 'a')
console.log(buf.includes(97));
// Prints: false
console.log(buf.includes(Buffer.from('a buffer example')));
// Prints: true
console.log(buf.includes(Buffer.from('a buffer example').slice(0, 8)));
// Prints: false
console.log(buf.includes('this', 4));
buf.indexOf(value[, byteOffset][, encoding])#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search forbyteOffset
<integer> Where to begin searching inbuf
. Default:0
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <integer> The index of the first occurrence of
value
inbuf
or-1
ifbuf
does not containvalue
If value
is:
- a string,
value
is interpreted according to the character encoding inencoding
. - a
Buffer
orUint8Array
,value
will be used in its entirety. To compare a partialBuffer
, usebuf.slice()
. - a number,
value
will be interpreted as an unsigned 8-bit integer value between0
and255
.
Examples:
const buf = Buffer.from('this is a buffer');
// Prints: 0
console.log(buf.indexOf('this'));
// Prints: 2
console.log(buf.indexOf('is'));
// Prints: 8
console.log(buf.indexOf(Buffer.from('a buffer')));
// Prints: 8
// (97 is the decimal ASCII value for 'a')
console.log(buf.indexOf(97));
// Prints: -1
console.log(buf.indexOf(Buffer.from('a buffer example')));
// Prints: 8
console.log(buf.indexOf(Buffer.from('a buffer example').slice(0, 8)));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
// Prints: 4
console.log(utf16Buffer.indexOf('\u03a3', 0, 'ucs2'));
// Prints: 6
console.log(utf16Buffer.indexOf('\u03a3', -4, 'ucs2'));
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
or 0, like {}
, []
, null
or undefined
, will search
the whole buffer. This behavior matches String#indexOf()
.
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.indexOf(99.9));
console.log(b.indexOf(256 + 99));
// Passing a byteOffset that coerces to NaN or 0
// Prints: 1, searching the whole buffer
console.log(b.indexOf('b', undefined));
console.log(b.indexOf('b', {}));
console.log(b.indexOf('b', null));
console.log(b.indexOf('b', []));
If value
is an empty string or empty Buffer
and byteOffset
is less
than buf.length
, byteOffset
will be returned. If value
is empty and
byteOffset
is at least buf.length
, buf.length
will be returned.
buf.keys()#
- Returns: <Iterator>
Creates and returns an iterator of buf
keys (indices).
Example:
const buf = Buffer.from('buffer');
// Prints:
// 0
// 1
// 2
// 3
// 4
// 5
for (const key of buf.keys()) {
console.log(key);
}
buf.lastIndexOf(value[, byteOffset][, encoding])#
value
<string> | <Buffer> | <Uint8Array> | <integer> What to search forbyteOffset
<integer> Where to begin searching inbuf
. Default:buf.length
- 1
encoding
<string> Ifvalue
is a string, this is its encoding. Default:'utf8'
- Returns: <integer> The index of the last occurrence of
value
inbuf
or-1
ifbuf
does not containvalue
Identical to buf.indexOf()
, except buf
is searched from back to front
instead of front to back.
Examples:
const buf = Buffer.from('this buffer is a buffer');
// Prints: 0
console.log(buf.lastIndexOf('this'));
// Prints: 17
console.log(buf.lastIndexOf('buffer'));
// Prints: 17
console.log(buf.lastIndexOf(Buffer.from('buffer')));
// Prints: 15
// (97 is the decimal ASCII value for 'a')
console.log(buf.lastIndexOf(97));
// Prints: -1
console.log(buf.lastIndexOf(Buffer.from('yolo')));
// Prints: 5
console.log(buf.lastIndexOf('buffer', 5));
// Prints: -1
console.log(buf.lastIndexOf('buffer', 4));
const utf16Buffer = Buffer.from('\u039a\u0391\u03a3\u03a3\u0395', 'ucs2');
// Prints: 6
console.log(utf16Buffer.lastIndexOf('\u03a3', undefined, 'ucs2'));
// Prints: 4
console.log(utf16Buffer.lastIndexOf('\u03a3', -5, 'ucs2'));
If value
is not a string, number, or Buffer
, this method will throw a
TypeError
. If value
is a number, it will be coerced to a valid byte value,
an integer between 0 and 255.
If byteOffset
is not a number, it will be coerced to a number. Any arguments
that coerce to NaN
, like {}
or undefined
, will search the whole buffer.
This behavior matches String#lastIndexOf()
.
const b = Buffer.from('abcdef');
// Passing a value that's a number, but not a valid byte
// Prints: 2, equivalent to searching for 99 or 'c'
console.log(b.lastIndexOf(99.9));
console.log(b.lastIndexOf(256 + 99));
// Passing a byteOffset that coerces to NaN
// Prints: 1, searching the whole buffer
console.log(b.lastIndexOf('b', undefined));
console.log(b.lastIndexOf('b', {}));
// Passing a byteOffset that coerces to 0
// Prints: -1, equivalent to passing 0
console.log(b.lastIndexOf('b', null));
console.log(b.lastIndexOf('b', []));
If value
is an empty string or empty Buffer
, byteOffset
will be returned.
buf.length#
Returns the amount of memory allocated for buf
in bytes. Note that this
does not necessarily reflect the amount of "usable" data within buf
.
Example: Create a Buffer
and write a shorter ASCII string to it
const buf = Buffer.alloc(1234);
// Prints: 1234
console.log(buf.length);
buf.write('some string', 0, 'ascii');
// Prints: 1234
console.log(buf.length);
While the length
property is not immutable, changing the value of length
can result in undefined and inconsistent behavior. Applications that wish to
modify the length of a Buffer
should therefore treat length
as read-only and
use buf.slice()
to create a new Buffer
.
Examples:
let buf = Buffer.allocUnsafe(10);
buf.write('abcdefghj', 0, 'ascii');
// Prints: 10
console.log(buf.length);
buf = buf.slice(0, 5);
// Prints: 5
console.log(buf.length);
buf.parent#
Stability: 0 - Deprecated: Use buf.buffer
instead.
The buf.parent
property is a deprecated alias for buf.buffer
.
buf.readDoubleBE(offset[, noAssert])#
buf.readDoubleLE(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 8
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <number>
Reads a 64-bit double from buf
at the specified offset
with specified
endian format (readDoubleBE()
returns big endian, readDoubleLE()
returns
little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([1, 2, 3, 4, 5, 6, 7, 8]);
// Prints: 8.20788039913184e-304
console.log(buf.readDoubleBE());
// Prints: 5.447603722011605e-270
console.log(buf.readDoubleLE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readDoubleLE(1));
// Warning: reads passed end of buffer!
// This will result in a segmentation fault! Don't do this!
console.log(buf.readDoubleLE(1, true));
buf.readFloatBE(offset[, noAssert])#
buf.readFloatLE(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <number>
Reads a 32-bit float from buf
at the specified offset
with specified
endian format (readFloatBE()
returns big endian, readFloatLE()
returns
little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([1, 2, 3, 4]);
// Prints: 2.387939260590663e-38
console.log(buf.readFloatBE());
// Prints: 1.539989614439558e-36
console.log(buf.readFloatLE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readFloatLE(1));
// Warning: reads passed end of buffer!
// This will result in a segmentation fault! Don't do this!
console.log(buf.readFloatLE(1, true));
buf.readInt8(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads a signed 8-bit integer from buf
at the specified offset
.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([-1, 5]);
// Prints: -1
console.log(buf.readInt8(0));
// Prints: 5
console.log(buf.readInt8(1));
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt8(2));
buf.readInt16BE(offset[, noAssert])#
buf.readInt16LE(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads a signed 16-bit integer from buf
at the specified offset
with
the specified endian format (readInt16BE()
returns big endian,
readInt16LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([0, 5]);
// Prints: 5
console.log(buf.readInt16BE());
// Prints: 1280
console.log(buf.readInt16LE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt16LE(1));
buf.readInt32BE(offset[, noAssert])#
buf.readInt32LE(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads a signed 32-bit integer from buf
at the specified offset
with
the specified endian format (readInt32BE()
returns big endian,
readInt32LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Integers read from a Buffer
are interpreted as two's complement signed values.
Examples:
const buf = Buffer.from([0, 0, 0, 5]);
// Prints: 5
console.log(buf.readInt32BE());
// Prints: 83886080
console.log(buf.readInt32LE());
// Throws an exception: RangeError: Index out of range
console.log(buf.readInt32LE(1));
buf.readIntBE(offset, byteLength[, noAssert])#
buf.readIntLE(offset, byteLength[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<integer> How many bytes to read. Must satisfy:0 < byteLength <= 6
noAssert
<boolean> Skipoffset
andbyteLength
validation? Default:false
- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as a two's complement signed value. Supports up to 48
bits of accuracy.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
// Prints: -546f87a9cbee
console.log(buf.readIntLE(0, 6).toString(16));
// Prints: 1234567890ab
console.log(buf.readIntBE(0, 6).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readIntBE(1, 6).toString(16));
buf.readUInt8(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads an unsigned 8-bit integer from buf
at the specified offset
.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([1, -2]);
// Prints: 1
console.log(buf.readUInt8(0));
// Prints: 254
console.log(buf.readUInt8(1));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt8(2));
buf.readUInt16BE(offset[, noAssert])#
buf.readUInt16LE(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads an unsigned 16-bit integer from buf
at the specified offset
with
specified endian format (readUInt16BE()
returns big endian, readUInt16LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56]);
// Prints: 1234
console.log(buf.readUInt16BE(0).toString(16));
// Prints: 3412
console.log(buf.readUInt16LE(0).toString(16));
// Prints: 3456
console.log(buf.readUInt16BE(1).toString(16));
// Prints: 5634
console.log(buf.readUInt16LE(1).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt16LE(2).toString(16));
buf.readUInt32BE(offset[, noAssert])#
buf.readUInt32LE(offset[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<boolean> Skipoffset
validation? Default:false
- Returns: <integer>
Reads an unsigned 32-bit integer from buf
at the specified offset
with
specified endian format (readUInt32BE()
returns big endian,
readUInt32LE()
returns little endian).
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78]);
// Prints: 12345678
console.log(buf.readUInt32BE(0).toString(16));
// Prints: 78563412
console.log(buf.readUInt32LE(0).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUInt32LE(1).toString(16));
buf.readUIntBE(offset, byteLength[, noAssert])#
buf.readUIntLE(offset, byteLength[, noAssert])#
offset
<integer> Where to start reading. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<integer> How many bytes to read. Must satisfy:0 < byteLength <= 6
noAssert
<boolean> Skipoffset
andbyteLength
validation? Default:false
- Returns: <integer>
Reads byteLength
number of bytes from buf
at the specified offset
and interprets the result as an unsigned integer. Supports up to 48
bits of accuracy.
Setting noAssert
to true
allows offset
to be beyond the end of buf
, but
the result should be considered undefined behavior.
Examples:
const buf = Buffer.from([0x12, 0x34, 0x56, 0x78, 0x90, 0xab]);
// Prints: 1234567890ab
console.log(buf.readUIntBE(0, 6).toString(16));
// Prints: ab9078563412
console.log(buf.readUIntLE(0, 6).toString(16));
// Throws an exception: RangeError: Index out of range
console.log(buf.readUIntBE(1, 6).toString(16));
buf.slice([start[, end]])#
start
<integer> Where the newBuffer
will start. Default:0
end
<integer> Where the newBuffer
will end (not inclusive). Default:buf.length
- Returns: <Buffer>
Returns a new Buffer
that references the same memory as the original, but
offset and cropped by the start
and end
indices.
Note: Modifying the new Buffer
slice will modify the memory in the
original Buffer
because the allocated memory of the two objects overlap.
Example: Create a Buffer
with the ASCII alphabet, take a slice, and then modify
one byte from the original Buffer
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
const buf2 = buf1.slice(0, 3);
// Prints: abc
console.log(buf2.toString('ascii', 0, buf2.length));
buf1[0] = 33;
// Prints: !bc
console.log(buf2.toString('ascii', 0, buf2.length));
Specifying negative indexes causes the slice to be generated relative to the
end of buf
rather than the beginning.
Examples:
const buf = Buffer.from('buffer');
// Prints: buffe
// (Equivalent to buf.slice(0, 5))
console.log(buf.slice(-6, -1).toString());
// Prints: buff
// (Equivalent to buf.slice(0, 4))
console.log(buf.slice(-6, -2).toString());
// Prints: uff
// (Equivalent to buf.slice(1, 4))
console.log(buf.slice(-5, -2).toString());
buf.swap16()#
- Returns: <Buffer> A reference to
buf
Interprets buf
as an array of unsigned 16-bit integers and swaps the byte-order
in-place. Throws a RangeError
if buf.length
is not a multiple of 2.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap16();
// Prints: <Buffer 02 01 04 03 06 05 08 07>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 16-bits
buf2.swap16();
buf.swap32()#
- Returns: <Buffer> A reference to
buf
Interprets buf
as an array of unsigned 32-bit integers and swaps the byte-order
in-place. Throws a RangeError
if buf.length
is not a multiple of 4.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap32();
// Prints: <Buffer 04 03 02 01 08 07 06 05>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 32-bits
buf2.swap32();
buf.swap64()#
- Returns: <Buffer> A reference to
buf
Interprets buf
as an array of 64-bit numbers and swaps the byte-order in-place.
Throws a RangeError
if buf.length
is not a multiple of 8.
Examples:
const buf1 = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5, 0x6, 0x7, 0x8]);
// Prints: <Buffer 01 02 03 04 05 06 07 08>
console.log(buf1);
buf1.swap64();
// Prints: <Buffer 08 07 06 05 04 03 02 01>
console.log(buf1);
const buf2 = Buffer.from([0x1, 0x2, 0x3]);
// Throws an exception: RangeError: Buffer size must be a multiple of 64-bits
buf2.swap64();
Note that JavaScript cannot encode 64-bit integers. This method is intended for working with 64-bit floats.
buf.toJSON()#
- Returns: <Object>
Returns a JSON representation of buf
. JSON.stringify()
implicitly calls
this function when stringifying a Buffer
instance.
Example:
const buf = Buffer.from([0x1, 0x2, 0x3, 0x4, 0x5]);
const json = JSON.stringify(buf);
// Prints: {"type":"Buffer","data":[1,2,3,4,5]}
console.log(json);
const copy = JSON.parse(json, (key, value) => {
return value && value.type === 'Buffer' ?
Buffer.from(value.data) :
value;
});
// Prints: <Buffer 01 02 03 04 05>
console.log(copy);
buf.toString([encoding[, start[, end]]])#
encoding
<string> The character encoding to decode to. Default:'utf8'
start
<integer> The byte offset to start decoding at. Default:0
end
<integer> The byte offset to stop decoding at (not inclusive). Default:buf.length
- Returns: <string>
Decodes buf
to a string according to the specified character encoding in
encoding
. start
and end
may be passed to decode only a subset of buf
.
The maximum length of a string instance (in UTF-16 code units) is available
as buffer.constants.MAX_STRING_LENGTH
.
Examples:
const buf1 = Buffer.allocUnsafe(26);
for (let i = 0; i < 26; i++) {
// 97 is the decimal ASCII value for 'a'
buf1[i] = i + 97;
}
// Prints: abcdefghijklmnopqrstuvwxyz
console.log(buf1.toString('ascii'));
// Prints: abcde
console.log(buf1.toString('ascii', 0, 5));
const buf2 = Buffer.from('tést');
// Prints: 74c3a97374
console.log(buf2.toString('hex'));
// Prints: té
console.log(buf2.toString('utf8', 0, 3));
// Prints: té
console.log(buf2.toString(undefined, 0, 3));
buf.values()#
- Returns: <Iterator>
Creates and returns an iterator for buf
values (bytes). This function is
called automatically when a Buffer
is used in a for..of
statement.
Examples:
const buf = Buffer.from('buffer');
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf.values()) {
console.log(value);
}
// Prints:
// 98
// 117
// 102
// 102
// 101
// 114
for (const value of buf) {
console.log(value);
}
buf.write(string[, offset[, length]][, encoding])#
string
<string> String to be written tobuf
offset
<integer> Where to start writingstring
. Default:0
length
<integer> How many bytes to write. Default:buf.length - offset
encoding
<string> The character encoding ofstring
. Default:'utf8'
- Returns: <integer> Number of bytes written
Writes string
to buf
at offset
according to the character encoding in encoding
.
The length
parameter is the number of bytes to write. If buf
did not contain
enough space to fit the entire string, only a partial amount of string
will
be written. However, partially encoded characters will not be written.
Example:
const buf = Buffer.allocUnsafe(256);
const len = buf.write('\u00bd + \u00bc = \u00be', 0);
// Prints: 12 bytes: ½ + ¼ = ¾
console.log(`${len} bytes: ${buf.toString('utf8', 0, len)}`);
buf.writeDoubleBE(value, offset[, noAssert])#
buf.writeDoubleLE(value, offset[, noAssert])#
value
<number> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 8
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeDoubleBE()
writes big endian, writeDoubleLE()
writes little
endian). value
should be a valid 64-bit double. Behavior is undefined when
value
is anything other than a 64-bit double.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(8);
buf.writeDoubleBE(0xdeadbeefcafebabe, 0);
// Prints: <Buffer 43 eb d5 b7 dd f9 5f d7>
console.log(buf);
buf.writeDoubleLE(0xdeadbeefcafebabe, 0);
// Prints: <Buffer d7 5f f9 dd b7 d5 eb 43>
console.log(buf);
buf.writeFloatBE(value, offset[, noAssert])#
buf.writeFloatLE(value, offset[, noAssert])#
value
<number> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeFloatBE()
writes big endian, writeFloatLE()
writes little
endian). value
should be a valid 32-bit float. Behavior is undefined when
value
is anything other than a 32-bit float.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeFloatBE(0xcafebabe, 0);
// Prints: <Buffer 4f 4a fe bb>
console.log(buf);
buf.writeFloatLE(0xcafebabe, 0);
// Prints: <Buffer bb fe 4a 4f>
console.log(buf);
buf.writeInt8(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
. value
should be a valid
signed 8-bit integer. Behavior is undefined when value
is anything other than
a signed 8-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(2);
buf.writeInt8(2, 0);
buf.writeInt8(-2, 1);
// Prints: <Buffer 02 fe>
console.log(buf);
buf.writeInt16BE(value, offset[, noAssert])#
buf.writeInt16LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeInt16BE()
writes big endian, writeInt16LE()
writes little
endian). value
should be a valid signed 16-bit integer. Behavior is undefined
when value
is anything other than a signed 16-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeInt16BE(0x0102, 0);
buf.writeInt16LE(0x0304, 2);
// Prints: <Buffer 01 02 04 03>
console.log(buf);
buf.writeInt32BE(value, offset[, noAssert])#
buf.writeInt32LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeInt32BE()
writes big endian, writeInt32LE()
writes little
endian). value
should be a valid signed 32-bit integer. Behavior is undefined
when value
is anything other than a signed 32-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
value
is interpreted and written as a two's complement signed integer.
Examples:
const buf = Buffer.allocUnsafe(8);
buf.writeInt32BE(0x01020304, 0);
buf.writeInt32LE(0x05060708, 4);
// Prints: <Buffer 01 02 03 04 08 07 06 05>
console.log(buf);
buf.writeIntBE(value, offset, byteLength[, noAssert])#
buf.writeIntLE(value, offset, byteLength[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<integer> How many bytes to write. Must satisfy:0 < byteLength <= 6
noAssert
<boolean> Skipvalue
,offset
, andbyteLength
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes byteLength
bytes of value
to buf
at the specified offset
.
Supports up to 48 bits of accuracy. Behavior is undefined when value
is
anything other than a signed integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);
buf.writeUIntLE(0x1234567890ab, 0, 6);
// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);
buf.writeUInt8(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 1
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
. value
should be a
valid unsigned 8-bit integer. Behavior is undefined when value
is anything
other than an unsigned 8-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt8(0x3, 0);
buf.writeUInt8(0x4, 1);
buf.writeUInt8(0x23, 2);
buf.writeUInt8(0x42, 3);
// Prints: <Buffer 03 04 23 42>
console.log(buf);
buf.writeUInt16BE(value, offset[, noAssert])#
buf.writeUInt16LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 2
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeUInt16BE()
writes big endian, writeUInt16LE()
writes little
endian). value
should be a valid unsigned 16-bit integer. Behavior is
undefined when value
is anything other than an unsigned 16-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt16BE(0xdead, 0);
buf.writeUInt16BE(0xbeef, 2);
// Prints: <Buffer de ad be ef>
console.log(buf);
buf.writeUInt16LE(0xdead, 0);
buf.writeUInt16LE(0xbeef, 2);
// Prints: <Buffer ad de ef be>
console.log(buf);
buf.writeUInt32BE(value, offset[, noAssert])#
buf.writeUInt32LE(value, offset[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - 4
noAssert
<boolean> Skipvalue
andoffset
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes value
to buf
at the specified offset
with specified endian
format (writeUInt32BE()
writes big endian, writeUInt32LE()
writes little
endian). value
should be a valid unsigned 32-bit integer. Behavior is
undefined when value
is anything other than an unsigned 32-bit integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(4);
buf.writeUInt32BE(0xfeedface, 0);
// Prints: <Buffer fe ed fa ce>
console.log(buf);
buf.writeUInt32LE(0xfeedface, 0);
// Prints: <Buffer ce fa ed fe>
console.log(buf);
buf.writeUIntBE(value, offset, byteLength[, noAssert])#
buf.writeUIntLE(value, offset, byteLength[, noAssert])#
value
<integer> Number to be written tobuf
offset
<integer> Where to start writing. Must satisfy:0 <= offset <= buf.length - byteLength
byteLength
<integer> How many bytes to write. Must satisfy:0 < byteLength <= 6
noAssert
<boolean> Skipvalue
,offset
, andbyteLength
validation? Default:false
- Returns: <integer>
offset
plus the number of bytes written
Writes byteLength
bytes of value
to buf
at the specified offset
.
Supports up to 48 bits of accuracy. Behavior is undefined when value
is
anything other than an unsigned integer.
Setting noAssert
to true
allows the encoded form of value
to extend beyond
the end of buf
, but the result should be considered undefined behavior.
Examples:
const buf = Buffer.allocUnsafe(6);
buf.writeUIntBE(0x1234567890ab, 0, 6);
// Prints: <Buffer 12 34 56 78 90 ab>
console.log(buf);
buf.writeUIntLE(0x1234567890ab, 0, 6);
// Prints: <Buffer ab 90 78 56 34 12>
console.log(buf);
buffer.INSPECT_MAX_BYTES#
- <integer> Default:
50
Returns the maximum number of bytes that will be returned when
buf.inspect()
is called. This can be overridden by user modules. See
util.inspect()
for more details on buf.inspect()
behavior.
Note that this is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
buffer.kMaxLength#
- <integer> The largest size allowed for a single
Buffer
instance
An alias for buffer.constants.MAX_LENGTH
Note that this is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
buffer.transcode(source, fromEnc, toEnc)#
source
<Buffer> | <Uint8Array> ABuffer
orUint8Array
instancefromEnc
<string> The current encodingtoEnc
<string> To target encoding
Re-encodes the given Buffer
or Uint8Array
instance from one character
encoding to another. Returns a new Buffer
instance.
Throws if the fromEnc
or toEnc
specify invalid character encodings or if
conversion from fromEnc
to toEnc
is not permitted.
The transcoding process will use substitution characters if a given byte sequence cannot be adequately represented in the target encoding. For instance:
const buffer = require('buffer');
const newBuf = buffer.transcode(Buffer.from('€'), 'utf8', 'ascii');
console.log(newBuf.toString('ascii'));
// Prints: '?'
Because the Euro (€
) sign is not representable in US-ASCII, it is replaced
with ?
in the transcoded Buffer
.
Note that this is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
Class: SlowBuffer#
Stability: 0 - Deprecated: Use Buffer.allocUnsafeSlow()
instead.
Returns an un-pooled Buffer
.
In order to avoid the garbage collection overhead of creating many individually
allocated Buffer
instances, by default allocations under 4KB are sliced from a
single larger allocated object. This approach improves both performance and memory
usage since v8 does not need to track and cleanup as many Persistent
objects.
In the case where a developer may need to retain a small chunk of memory from a
pool for an indeterminate amount of time, it may be appropriate to create an
un-pooled Buffer
instance using SlowBuffer
then copy out the relevant bits.
Example:
// Need to keep around a few small chunks of memory
const store = [];
socket.on('readable', () => {
const data = socket.read();
// Allocate for retained data
const sb = SlowBuffer(10);
// Copy the data into the new allocation
data.copy(sb, 0, 0, 10);
store.push(sb);
});
Use of SlowBuffer
should be used only as a last resort after a developer
has observed undue memory retention in their applications.
new SlowBuffer(size)#
Stability: 0 - Deprecated: Use Buffer.allocUnsafeSlow()
instead.
size
<integer> The desired length of the newSlowBuffer
Allocates a new Buffer
of size
bytes. If the size
is larger than
buffer.constants.MAX_LENGTH
or smaller than 0, a RangeError
will be
thrown. A zero-length Buffer
will be created if size
is 0.
The underlying memory for SlowBuffer
instances is not initialized. The
contents of a newly created SlowBuffer
are unknown and may contain
sensitive data. Use buf.fill(0)
to initialize a SlowBuffer
to zeroes.
Example:
const { SlowBuffer } = require('buffer');
const buf = new SlowBuffer(5);
// Prints: (contents may vary): <Buffer 78 e0 82 02 01>
console.log(buf);
buf.fill(0);
// Prints: <Buffer 00 00 00 00 00>
console.log(buf);
Buffer Constants#
Note that buffer.constants
is a property on the buffer
module returned by
require('buffer')
, not on the Buffer
global or a Buffer
instance.
buffer.constants.MAX_LENGTH#
- <integer> The largest size allowed for a single
Buffer
instance
On 32-bit architectures, this value is (2^30)-1
(~1GB).
On 64-bit architectures, this value is (2^31)-1
(~2GB).
This value is also available as buffer.kMaxLength
.
buffer.constants.MAX_STRING_LENGTH#
- <integer> The largest length allowed for a single
string
instance
Represents the largest length
that a string
primitive can have, counted
in UTF-16 code units.
This value may depend on the JS engine that is being used.
C++ Addons#
Node.js Addons are dynamically-linked shared objects, written in C++, that
can be loaded into Node.js using the require()
function, and used
just as if they were an ordinary Node.js module. They are used primarily to
provide an interface between JavaScript running in Node.js and C/C++ libraries.
At the moment, the method for implementing Addons is rather complicated, involving knowledge of several components and APIs :
V8: the C++ library Node.js currently uses to provide the JavaScript implementation. V8 provides the mechanisms for creating objects, calling functions, etc. V8's API is documented mostly in the
v8.h
header file (deps/v8/include/v8.h
in the Node.js source tree), which is also available online.libuv: The C library that implements the Node.js event loop, its worker threads and all of the asynchronous behaviors of the platform. It also serves as a cross-platform abstraction library, giving easy, POSIX-like access across all major operating systems to many common system tasks, such as interacting with the filesystem, sockets, timers and system events. libuv also provides a pthreads-like threading abstraction that may be used to power more sophisticated asynchronous Addons that need to move beyond the standard event loop. Addon authors are encouraged to think about how to avoid blocking the event loop with I/O or other time-intensive tasks by off-loading work via libuv to non-blocking system operations, worker threads or a custom use of libuv's threads.
Internal Node.js libraries. Node.js itself exports a number of C++ APIs that Addons can use — the most important of which is the
node::ObjectWrap
class.Node.js includes a number of other statically linked libraries including OpenSSL. These other libraries are located in the
deps/
directory in the Node.js source tree. Only the V8 and OpenSSL symbols are purposefully re-exported by Node.js and may be used to various extents by Addons. See Linking to Node.js' own dependencies for additional information.
All of the following examples are available for download and may be used as the starting-point for an Addon.
Hello world#
This "Hello world" example is a simple Addon, written in C++, that is the equivalent of the following JavaScript code:
module.exports.hello = () => 'world';
First, create the file hello.cc
:
// hello.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void Method(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "world"));
}
void init(Local<Object> exports) {
NODE_SET_METHOD(exports, "hello", Method);
}
NODE_MODULE(addon, init)
} // namespace demo
Note that all Node.js Addons must export an initialization function following the pattern:
void Initialize(Local<Object> exports);
NODE_MODULE(module_name, Initialize)
There is no semi-colon after NODE_MODULE
as it's not a function (see
node.h
).
The module_name
must match the filename of the final binary (excluding
the .node suffix).
In the hello.cc
example, then, the initialization function is init
and the
Addon module name is addon
.
Building#
Once the source code has been written, it must be compiled into the binary
addon.node
file. To do so, create a file called binding.gyp
in the
top-level of the project describing the build configuration of the module
using a JSON-like format. This file is used by node-gyp -- a tool written
specifically to compile Node.js Addons.
{
"targets": [
{
"target_name": "addon",
"sources": [ "hello.cc" ]
}
]
}
Note: A version of the node-gyp
utility is bundled and distributed with
Node.js as part of npm
. This version is not made directly available for
developers to use and is intended only to support the ability to use the
npm install
command to compile and install Addons. Developers who wish to
use node-gyp
directly can install it using the command
npm install -g node-gyp
. See the node-gyp
installation instructions for
more information, including platform-specific requirements.
Once the binding.gyp
file has been created, use node-gyp configure
to
generate the appropriate project build files for the current platform. This
will generate either a Makefile
(on Unix platforms) or a vcxproj
file
(on Windows) in the build/
directory.
Next, invoke the node-gyp build
command to generate the compiled addon.node
file. This will be put into the build/Release/
directory.
When using npm install
to install a Node.js Addon, npm uses its own bundled
version of node-gyp
to perform this same set of actions, generating a
compiled version of the Addon for the user's platform on demand.
Once built, the binary Addon can be used from within Node.js by pointing
require()
to the built addon.node
module:
// hello.js
const addon = require('./build/Release/addon');
console.log(addon.hello());
// Prints: 'world'
Please see the examples below for further information or https://github.com/arturadib/node-qt for an example in production.
Because the exact path to the compiled Addon binary can vary depending on how
it is compiled (i.e. sometimes it may be in ./build/Debug/
), Addons can use
the bindings package to load the compiled module.
Note that while the bindings
package implementation is more sophisticated
in how it locates Addon modules, it is essentially using a try-catch pattern
similar to:
try {
return require('./build/Release/addon.node');
} catch (err) {
return require('./build/Debug/addon.node');
}
Linking to Node.js' own dependencies#
Node.js uses a number of statically linked libraries such as V8, libuv and
OpenSSL. All Addons are required to link to V8 and may link to any of the
other dependencies as well. Typically, this is as simple as including
the appropriate #include <...>
statements (e.g. #include <v8.h>
) and
node-gyp
will locate the appropriate headers automatically. However, there
are a few caveats to be aware of:
When
node-gyp
runs, it will detect the specific release version of Node.js and download either the full source tarball or just the headers. If the full source is downloaded, Addons will have complete access to the full set of Node.js dependencies. However, if only the Node.js headers are downloaded, then only the symbols exported by Node.js will be available.node-gyp
can be run using the--nodedir
flag pointing at a local Node.js source image. Using this option, the Addon will have access to the full set of dependencies.
Loading Addons using require()#
The filename extension of the compiled Addon binary is .node
(as opposed
to .dll
or .so
). The require()
function is written to look for
files with the .node
file extension and initialize those as dynamically-linked
libraries.
When calling require()
, the .node
extension can usually be
omitted and Node.js will still find and initialize the Addon. One caveat,
however, is that Node.js will first attempt to locate and load modules or
JavaScript files that happen to share the same base name. For instance, if
there is a file addon.js
in the same directory as the binary addon.node
,
then require('addon')
will give precedence to the addon.js
file
and load it instead.
Native Abstractions for Node.js#
Each of the examples illustrated in this document make direct use of the Node.js and V8 APIs for implementing Addons. It is important to understand that the V8 API can, and has, changed dramatically from one V8 release to the next (and one major Node.js release to the next). With each change, Addons may need to be updated and recompiled in order to continue functioning. The Node.js release schedule is designed to minimize the frequency and impact of such changes but there is little that Node.js can do currently to ensure stability of the V8 APIs.
The Native Abstractions for Node.js (or nan
) provide a set of tools that
Addon developers are recommended to use to keep compatibility between past and
future releases of V8 and Node.js. See the nan
examples for an
illustration of how it can be used.
N-API#
Stability: 1 - Experimental
N-API is an API for building native Addons. It is independent from the underlying JavaScript runtime (ex V8) and is maintained as part of Node.js itself. This API will be Application Binary Interface (ABI) stable across version of Node.js. It is intended to insulate Addons from changes in the underlying JavaScript engine and allow modules compiled for one version to run on later versions of Node.js without recompilation. Addons are built/packaged with the same approach/tools outlined in this document (node-gyp, etc.). The only difference is the set of APIs that are used by the native code. Instead of using the V8 or Native Abstractions for Node.js APIs, the functions available in the N-API are used.
The functions available and how to use them are documented in the section titled C/C++ Addons - N-API.
Addon examples#
Following are some example Addons intended to help developers get started. The examples make use of the V8 APIs. Refer to the online V8 reference for help with the various V8 calls, and V8's Embedder's Guide for an explanation of several concepts used such as handles, scopes, function templates, etc.
Each of these examples using the following binding.gyp
file:
{
"targets": [
{
"target_name": "addon",
"sources": [ "addon.cc" ]
}
]
}
In cases where there is more than one .cc
file, simply add the additional
filename to the sources
array. For example:
"sources": ["addon.cc", "myexample.cc"]
Once the binding.gyp
file is ready, the example Addons can be configured and
built using node-gyp
:
$ node-gyp configure build
Function arguments#
Addons will typically expose objects and functions that can be accessed from JavaScript running within Node.js. When functions are invoked from JavaScript, the input arguments and return value must be mapped to and from the C/C++ code.
The following example illustrates how to read function arguments passed from JavaScript and how to return a result:
// addon.cc
#include <node.h>
namespace demo {
using v8::Exception;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
// This is the implementation of the "add" method
// Input arguments are passed using the
// const FunctionCallbackInfo<Value>& args struct
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
// Check the number of arguments passed.
if (args.Length() < 2) {
// Throw an Error that is passed back to JavaScript
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong number of arguments")));
return;
}
// Check the argument types
if (!args[0]->IsNumber() || !args[1]->IsNumber()) {
isolate->ThrowException(Exception::TypeError(
String::NewFromUtf8(isolate, "Wrong arguments")));
return;
}
// Perform the operation
double value = args[0]->NumberValue() + args[1]->NumberValue();
Local<Number> num = Number::New(isolate, value);
// Set the return value (using the passed in
// FunctionCallbackInfo<Value>&)
args.GetReturnValue().Set(num);
}
void Init(Local<Object> exports) {
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, Init)
} // namespace demo
Once compiled, the example Addon can be required and used from within Node.js:
// test.js
const addon = require('./build/Release/addon');
console.log('This should be eight:', addon.add(3, 5));
Callbacks#
It is common practice within Addons to pass JavaScript functions to a C++ function and execute them from there. The following example illustrates how to invoke such callbacks:
// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Null;
using v8::Object;
using v8::String;
using v8::Value;
void RunCallback(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Function> cb = Local<Function>::Cast(args[0]);
const unsigned argc = 1;
Local<Value> argv[argc] = { String::NewFromUtf8(isolate, "hello world") };
cb->Call(Null(isolate), argc, argv);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", RunCallback);
}
NODE_MODULE(addon, Init)
} // namespace demo
Note that this example uses a two-argument form of Init()
that receives
the full module
object as the second argument. This allows the Addon
to completely overwrite exports
with a single function instead of
adding the function as a property of exports
.
To test it, run the following JavaScript:
// test.js
const addon = require('./build/Release/addon');
addon((msg) => {
console.log(msg);
// Prints: 'hello world'
});
Note that, in this example, the callback function is invoked synchronously.
Object factory#
Addons can create and return new objects from within a C++ function as
illustrated in the following example. An object is created and returned with a
property msg
that echoes the string passed to createObject()
:
// addon.cc
#include <node.h>
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<Object> obj = Object::New(isolate);
obj->Set(String::NewFromUtf8(isolate, "msg"), args[0]->ToString());
args.GetReturnValue().Set(obj);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, Init)
} // namespace demo
To test it in JavaScript:
// test.js
const addon = require('./build/Release/addon');
const obj1 = addon('hello');
const obj2 = addon('world');
console.log(obj1.msg, obj2.msg);
// Prints: 'hello world'
Function factory#
Another common scenario is creating JavaScript functions that wrap C++ functions and returning those back to JavaScript:
// addon.cc
#include <node.h>
namespace demo {
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void MyFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
args.GetReturnValue().Set(String::NewFromUtf8(isolate, "hello world"));
}
void CreateFunction(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, MyFunction);
Local<Function> fn = tpl->GetFunction();
// omit this to make it anonymous
fn->SetName(String::NewFromUtf8(isolate, "theFunction"));
args.GetReturnValue().Set(fn);
}
void Init(Local<Object> exports, Local<Object> module) {
NODE_SET_METHOD(module, "exports", CreateFunction);
}
NODE_MODULE(addon, Init)
} // namespace demo
To test:
// test.js
const addon = require('./build/Release/addon');
const fn = addon();
console.log(fn());
// Prints: 'hello world'
Wrapping C++ objects#
It is also possible to wrap C++ objects/classes in a way that allows new
instances to be created using the JavaScript new
operator:
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Local;
using v8::Object;
void InitAll(Local<Object> exports) {
MyObject::Init(exports);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
Then, in myobject.h
, the wrapper class inherits from node::ObjectWrap
:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Local<v8::Object> exports);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
In myobject.cc
, implement the various methods that are to be exposed.
Below, the method plusOne()
is exposed by adding it to the constructor's
prototype:
// myobject.cc
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Local<Object> exports) {
Isolate* isolate = exports->GetIsolate();
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
exports->Set(String::NewFromUtf8(isolate, "MyObject"),
tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> result =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(result);
}
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
To build this example, the myobject.cc
file must be added to the
binding.gyp
:
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
Test it with:
// test.js
const addon = require('./build/Release/addon');
const obj = new addon.MyObject(10);
console.log(obj.plusOne());
// Prints: 11
console.log(obj.plusOne());
// Prints: 12
console.log(obj.plusOne());
// Prints: 13
Factory of wrapped objects#
Alternatively, it is possible to use a factory pattern to avoid explicitly
creating object instances using the JavaScript new
operator:
const obj = addon.createObject();
// instead of:
// const obj = new addon.Object();
First, the createObject()
method is implemented in addon.cc
:
// addon.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void InitAll(Local<Object> exports, Local<Object> module) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(module, "exports", CreateObject);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
In myobject.h
, the static method NewInstance()
is added to handle
instantiating the object. This method takes the place of using new
in
JavaScript:
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static void PlusOne(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
The implementation in myobject.cc
is similar to the previous example:
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
// Prototype
NODE_SET_PROTOTYPE_METHOD(tpl, "plusOne", PlusOne);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
void MyObject::PlusOne(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj = ObjectWrap::Unwrap<MyObject>(args.Holder());
obj->value_ += 1;
args.GetReturnValue().Set(Number::New(isolate, obj->value_));
}
} // namespace demo
Once again, to build this example, the myobject.cc
file must be added to the
binding.gyp
:
{
"targets": [
{
"target_name": "addon",
"sources": [
"addon.cc",
"myobject.cc"
]
}
]
}
Test it with:
// test.js
const createObject = require('./build/Release/addon');
const obj = createObject(10);
console.log(obj.plusOne());
// Prints: 11
console.log(obj.plusOne());
// Prints: 12
console.log(obj.plusOne());
// Prints: 13
const obj2 = createObject(20);
console.log(obj2.plusOne());
// Prints: 21
console.log(obj2.plusOne());
// Prints: 22
console.log(obj2.plusOne());
// Prints: 23
Passing wrapped objects around#
In addition to wrapping and returning C++ objects, it is possible to pass
wrapped objects around by unwrapping them with the Node.js helper function
node::ObjectWrap::Unwrap
. The following examples shows a function add()
that can take two MyObject
objects as input arguments:
// addon.cc
#include <node.h>
#include <node_object_wrap.h>
#include "myobject.h"
namespace demo {
using v8::FunctionCallbackInfo;
using v8::Isolate;
using v8::Local;
using v8::Number;
using v8::Object;
using v8::String;
using v8::Value;
void CreateObject(const FunctionCallbackInfo<Value>& args) {
MyObject::NewInstance(args);
}
void Add(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
MyObject* obj1 = node::ObjectWrap::Unwrap<MyObject>(
args[0]->ToObject());
MyObject* obj2 = node::ObjectWrap::Unwrap<MyObject>(
args[1]->ToObject());
double sum = obj1->value() + obj2->value();
args.GetReturnValue().Set(Number::New(isolate, sum));
}
void InitAll(Local<Object> exports) {
MyObject::Init(exports->GetIsolate());
NODE_SET_METHOD(exports, "createObject", CreateObject);
NODE_SET_METHOD(exports, "add", Add);
}
NODE_MODULE(addon, InitAll)
} // namespace demo
In myobject.h
, a new public method is added to allow access to private values
after unwrapping the object.
// myobject.h
#ifndef MYOBJECT_H
#define MYOBJECT_H
#include <node.h>
#include <node_object_wrap.h>
namespace demo {
class MyObject : public node::ObjectWrap {
public:
static void Init(v8::Isolate* isolate);
static void NewInstance(const v8::FunctionCallbackInfo<v8::Value>& args);
inline double value() const { return value_; }
private:
explicit MyObject(double value = 0);
~MyObject();
static void New(const v8::FunctionCallbackInfo<v8::Value>& args);
static v8::Persistent<v8::Function> constructor;
double value_;
};
} // namespace demo
#endif
The implementation of myobject.cc
is similar to before:
// myobject.cc
#include <node.h>
#include "myobject.h"
namespace demo {
using v8::Context;
using v8::Function;
using v8::FunctionCallbackInfo;
using v8::FunctionTemplate;
using v8::Isolate;
using v8::Local;
using v8::Object;
using v8::Persistent;
using v8::String;
using v8::Value;
Persistent<Function> MyObject::constructor;
MyObject::MyObject(double value) : value_(value) {
}
MyObject::~MyObject() {
}
void MyObject::Init(Isolate* isolate) {
// Prepare constructor template
Local<FunctionTemplate> tpl = FunctionTemplate::New(isolate, New);
tpl->SetClassName(String::NewFromUtf8(isolate, "MyObject"));
tpl->InstanceTemplate()->SetInternalFieldCount(1);
constructor.Reset(isolate, tpl->GetFunction());
}
void MyObject::New(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
if (args.IsConstructCall()) {
// Invoked as constructor: `new MyObject(...)`
double value = args[0]->IsUndefined() ? 0 : args[0]->NumberValue();
MyObject* obj = new MyObject(value);
obj->Wrap(args.This());
args.GetReturnValue().Set(args.This());
} else {
// Invoked as plain function `MyObject(...)`, turn into construct call.
const int argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Context> context = isolate->GetCurrentContext();
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
}
void MyObject::NewInstance(const FunctionCallbackInfo<Value>& args) {
Isolate* isolate = args.GetIsolate();
const unsigned argc = 1;
Local<Value> argv[argc] = { args[0] };
Local<Function> cons = Local<Function>::New(isolate, constructor);
Local<Context> context = isolate->GetCurrentContext();
Local<Object> instance =
cons->NewInstance(context, argc, argv).ToLocalChecked();
args.GetReturnValue().Set(instance);
}
} // namespace demo
Test it with:
// test.js
const addon = require('./build/Release/addon');
const obj1 = addon.createObject(10);
const obj2 = addon.createObject(20);
const result = addon.add(obj1, obj2);
console.log(result);
// Prints: 30
AtExit hooks#
An "AtExit" hook is a function that is invoked after the Node.js event loop
has ended but before the JavaScript VM is terminated and Node.js shuts down.
"AtExit" hooks are registered using the node::AtExit
API.
void AtExit(callback, args)#
callback
:void (*)(void*)
- A pointer to the function to call at exit.args
:void*
- A pointer to pass to the callback at exit.
Registers exit hooks that run after the event loop has ended but before the VM is killed.
AtExit takes two parameters: a pointer to a callback function to run at exit, and a pointer to untyped context data to be passed to that callback.
Callbacks are run in last-in first-out order.
The following addon.cc
implements AtExit:
// addon.cc
#undef NDEBUG
#include <assert.h>
#include <stdlib.h>
#include <node.h>
namespace demo {
using node::AtExit;
using v8::HandleScope;
using v8::Isolate;
using v8::Local;
using v8::Object;
static char cookie[] = "yum yum";
static int at_exit_cb1_called = 0;
static int at_exit_cb2_called = 0;
static void at_exit_cb1(void* arg) {
Isolate* isolate = static_cast<Isolate*>(arg);
HandleScope scope(isolate);
Local<Object> obj = Object::New(isolate);
assert(!obj.IsEmpty()); // assert VM is still alive
assert(obj->IsObject());
at_exit_cb1_called++;
}
static void at_exit_cb2(void* arg) {
assert(arg == static_cast<void*>(cookie));
at_exit_cb2_called++;
}
static void sanity_check(void*) {
assert(at_exit_cb1_called == 1);
assert(at_exit_cb2_called == 2);
}
void init(Local<Object> exports) {
AtExit(sanity_check);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb2, cookie);
AtExit(at_exit_cb1, exports->GetIsolate());
}
NODE_MODULE(addon, init)
} // namespace demo
Test in JavaScript by running:
// test.js
const addon = require('./build/Release/addon');
N-API#
Stability: 1 - Experimental
N-API (pronounced N as in the letter, followed by API) is an API for building native Addons. It is independent from the underlying JavaScript runtime (ex V8) and is maintained as part of Node.js itself. This API will be Application Binary Interface (ABI) stable across versions of Node.js. It is intended to insulate Addons from changes in the underlying JavaScript engine and allow modules compiled for one version to run on later versions of Node.js without recompilation.
Addons are built/packaged with the same approach/tools outlined in the section titled C++ Addons. The only difference is the set of APIs that are used by the native code. Instead of using the V8 or Native Abstractions for Node.js APIs, the functions available in the N-API are used.
APIs exposed by N-API are generally used to create and manipulate JavaScript values. Concepts and operations generally map to ideas specified in the ECMA262 Language Specification. The APIs have the following properties:
- All N-API calls return a status code of type
napi_status
. This status indicates whether the API call succeeded or failed. - The API's return value is passed via an out parameter.
- All JavaScript values are abstracted behind an opaque type named
napi_value
. - In case of an error status code, additional information can be obtained
using
napi_get_last_error_info
. More information can be found in the error handling section Error Handling.
The documentation for N-API is structured as follows:
- Basic N-API Data Types
- Error Handling
- Object Lifetime Management
- Module Registration
- Working with JavaScript Values
- Working with JavaScript Values - Abstract Operations
- Working with JavaScript Properties
- Working with JavaScript Functions
- Object Wrap
- Asynchronous Operations
The N-API is a C API that ensures ABI stability across Node.js versions and different compiler levels. However, we also understand that a C++ API can be easier to use in many cases. To support these cases we expect there to be one or more C++ wrapper modules that provide an inlineable C++ API. Binaries built with these wrapper modules will depend on the symbols for the N-API C based functions exported by Node.js. These wrappers are not part of N-API, nor will they be maintained as part of Node.js. One such example is: node-api.
In order to use the N-API functions, include the file node_api.h which is located in the src directory in the node development tree. For example:
#include <node_api.h>
As the feature is experimental it must be enabled with the following command line option:
--napi-modules
Basic N-API Data Types#
N-API exposes the following fundamental datatypes as abstractions that are consumed by the various APIs. These APIs should be treated as opaque, introspectable only with other N-API calls.
napi_status#
Integral status code indicating the success or failure of a N-API call. Currently, the following status codes are supported.
typedef enum {
napi_ok,
napi_invalid_arg,
napi_object_expected,
napi_string_expected,
napi_name_expected,
napi_function_expected,
napi_number_expected,
napi_boolean_expected,
napi_array_expected,
napi_generic_failure,
napi_pending_exception,
napi_cancelled,
napi_status_last
} napi_status;
If additional information is required upon an API returning a failed status,
it can be obtained by calling napi_get_last_error_info
.
napi_extended_error_info#
typedef struct {
const char* error_message;
void* engine_reserved;
uint32_t engine_error_code;
napi_status error_code;
} napi_extended_error_info;
error_message
: UTF8-encoded string containing a VM-neutral description of the error.engine_reserved
: Reserved for VM-specific error details. This is currently not implemented for any VM.engine_error_code
: VM-specific error code. This is currently not implemented for any VM.error_code
: The N-API status code that originated with the last error.
See the Error Handling section for additional information.
napi_env#
napi_env
is used to represent a context that the underlying N-API
implementation can use to persist VM-specific state. This structure is passed
to native functions when they're invoked, and it must be passed back when
making N-API calls. Specifically, the same napi_env
that was passed in when
the initial native function was called must be passed to any subsequent
nested N-API calls. Caching the napi_env
for the purpose of general reuse is
not allowed.
napi_value#
This is an opaque pointer that is used to represent a JavaScript value.
N-API Memory Management types#
napi_handle_scope#
This is an abstraction used to control and modify the lifetime of objects created within a particular scope. In general, N-API values are created within the context of a handle scope. When a native method is called from JavaScript, a default handle scope will exist. If the user does not explicitly create a new handle scope, N-API values will be created in the default handle scope. For any invocations of code outside the execution of a native method (for instance, during a libuv callback invocation), the module is required to create a scope before invoking any functions that can result in the creation of JavaScript values.
Handle scopes are created using napi_open_handle_scope
and are destroyed
using napi_close_handle_scope
. Closing the scope can indicate to the GC that
all napi_value
s created during the lifetime of the handle scope are no longer
referenced from the current stack frame.
For more details, review the Object Lifetime Management.
napi_escapable_handle_scope#
Escapable handle scopes are a special type of handle scope to return values created within a particular handle scope to a parent scope.
napi_ref#
This is the abstraction to use to reference a napi_value
. This allows for
users to manage the lifetimes of JavaScript values, including defining their
minimum lifetimes explicitly.
For more details, review the Object Lifetime Management.
N-API Callback types#
napi_callback_info#
Opaque datatype that is passed to a callback function. It can be used for getting additional information about the context in which the callback was invoked.
napi_callback#
Function pointer type for user-provided native functions which are to be exposed to JavaScript via N-API. Callback functions should satisfy the following signature:
typedef napi_value (*napi_callback)(napi_env, napi_callback_info);
napi_finalize#
Function pointer type for add-on provided functions that allow the user to be
notified when externally-owned data is ready to be cleaned up because the
object with which it was associated with, has been garbage-collected. The user
must provide a function satisfying the following signature which would get
called upon the object's collection. Currently, napi_finalize
can be used for
finding out when objects that have external data are collected.
napi_async_execute_callback#
Function pointer used with functions that support asynchronous operations. Callback functions must statisfy the following signature:
typedef void (*napi_async_execute_callback)(napi_env env, void* data);
napi_async_complete_callback#
Function pointer used with functions that support asynchronous operations. Callback functions must statisfy the following signature:
typedef void (*napi_async_complete_callback)(napi_env env,
napi_status status,
void* data);
Error Handling#
N-API uses both return values and Javascript exceptions for error handling. The following sections explain the approach for each case.
Return values#
All of the N-API functions share the same error handling pattern. The
return type of all API functions is napi_status
.
The return value will be napi_ok
if the request was successful and
no uncaught JavaScript exception was thrown. If an error occurred AND
an exception was thrown, the napi_status
value for the error
will be returned. If an exception was thrown, and no error occurred,
napi_pending_exception
will be returned.
In cases where a return value other than napi_ok
or
napi_pending_exception
is returned, napi_is_exception_pending
must be called to check if an exception is pending.
See the section on exceptions for more details.
The full set of possible napi_status values is defined
in napi_api_types.h
.
The napi_status
return value provides a VM-independent representation of
the error which occurred. In some cases it is useful to be able to get
more detailed information, including a string representing the error as well as
VM (engine)-specific information.
In order to retrieve this information napi_get_last_error_info
is provided which returns a napi_extended_error_info
structure.
The format of the napi_extended_error_info
structure is as follows:
typedef struct napi_extended_error_info {
const char* error_message;
void* engine_reserved;
uint32_t engine_error_code;
napi_status error_code;
};
error_message
: Textual representation of the error that occurred.engine_reserved
: Opaque handle reserved for engine use only.engine_error_code
: VM specific error code.error_code
: n-api status code for the last error.
napi_get_last_error_info
returns the information for the last
N-API call that was made.
Note: Do not rely on the content or format of any of the extended information as it is not subject to SemVer and may change at any time. It is intended only for logging purposes.
napi_get_last_error_info#
NAPI_EXTERN napi_status
napi_get_last_error_info(napi_env env,
const napi_extended_error_info** result);
[in] env
: The environment that the API is invoked under.[out] result
: Thenapi_extended_error_info
structure with more information about the error.
Returns napi_ok
if the API succeeded.
This API retrieves a napi_extended_error_info
structure with information
about the last error that occurred.
Note: The content of the napi_extended_error_info
returned is only
valid up until an n-api function is called on the same env
.
Note: Do not rely on the content or format of any of the extended information as it is not subject to SemVer and may change at any time. It is intended only for logging purposes.
Exceptions#
Any N-API function call may result in a pending JavaScript exception. This is obviously the case for any function that may cause the execution of JavaScript, but N-API specifies that an exception may be pending on return from any of the API functions.
If the napi_status
returned by a function is napi_ok
then no
exception is pending and no additional action is required. If the
napi_status
returned is anything other than napi_ok
or
napi_pending_exception
, in order to try to recover and continue
instead of simply returning immediately, napi_is_exception_pending
must be called in order to determine if an exception is pending or not.
When an exception is pending one of two approaches can be employed.
The first appoach is to do any appropriate cleanup and then return so that
execution will return to JavaScript. As part of the transition back to
JavaScript the exception will be thrown at the point in the JavaScript
code where the native method was invoked. The behavior of most N-API calls
is unspecified while an exception is pending, and many will simply return
napi_pending_exception
, so it is important to do as little as possible
and then return to JavaScript where the exception can be handled.
The second approach is to try to handle the exception. There will be cases
where the native code can catch the exception, take the appropriate action,
and then continue. This is only recommended in specific cases
where it is known that the exception can be safely handled. In these
cases napi_get_and_clear_last_exception
can be used to get and
clear the exception. On success, result will contain the handle to
the last JavaScript Object thrown. If it is determined, after
retrieving the exception, the exception cannot be handled after all
it can be re-thrown it with [napi_throw
][] where error is the
JavaScript Error object to be thrown.
The following utility functions are also available in case native code
needs to throw an exception or determine if a napi_value
is an instance
of a JavaScript Error
object: napi_throw_error
,
napi_throw_type_error
, napi_throw_range_error
and
napi_is_error
.
The following utility functions are also available in case native
code needs to create an Error object: napi_create_error
,
napi_create_type_error
, and napi_create_range_error
.
where result is the napi_value that refers to the newly created
JavaScript Error object.
napi_throw#
NODE_EXTERN napi_status napi_throw(napi_env env, napi_value error);
[in] env
: The environment that the API is invoked under.[in] error
: Thenapi_value
for the Error to be thrown.
Returns napi_ok
if the API succeeded.
This API throws the JavaScript Error provided.
napi_throw_error#
NODE_EXTERN napi_status napi_throw_error(napi_env env, const char* msg);
[in] env
: The environment that the API is invoked under.[in] msg
: C string representing the text to be associated with the error.
Returns napi_ok
if the API succeeded.
This API throws a JavaScript Error with the text provided.
napi_throw_type_error#
NODE_EXTERN napi_status napi_throw_type_error(napi_env env, const char* msg);
[in] env
: The environment that the API is invoked under.[in] msg
: C string representing the text to be associated with the error.
Returns napi_ok
if the API succeeded.
This API throws a JavaScript TypeError with the text provided.
napi_throw_range_error#
NODE_EXTERN napi_status napi_throw_range_error(napi_env env, const char* msg);
[in] env
: The environment that the API is invoked under.[in] msg
: C string representing the text to be associated with the error.
Returns napi_ok
if the API succeeded.
This API throws a JavaScript RangeError with the text provided.
napi_is_error#
NODE_EXTERN napi_status napi_is_error(napi_env env,
napi_value value,
bool* result);
[in] env
: The environment that the API is invoked under.[in] msg
: Thenapi_value
to be checked.[out] result
: Boolean value that is set to true ifnapi_value
represents an error, false otherwise.
Returns napi_ok
if the API succeeded.
This API queries a napi_value
to check if it represents an error object.
napi_create_error#
NODE_EXTERN napi_status napi_create_error(napi_env env,
napi_value msg,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] msg
: napi_value that references a JavaScript String to be used as the message for the Error.[out] result
:napi_value
representing the error created.
Returns napi_ok
if the API succeeded.
This API returns a JavaScript Error with the text provided.
napi_create_type_error#
NODE_EXTERN napi_status napi_create_type_error(napi_env env,
napi_value msg,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] msg
: napi_value that references a JavaScript String to be used as the message for the Error.[out] result
:napi_value
representing the error created.
Returns napi_ok
if the API succeeded.
This API returns a JavaScript TypeError with the text provided.
napi_create_range_error#
NODE_EXTERN napi_status napi_create_range_error(napi_env env,
const char* msg,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] msg
: napi_value that references a JavaScript String to be used as the message for the Error.[out] result
:napi_value
representing the error created.
Returns napi_ok
if the API succeeded.
This API returns a JavaScript RangeError with the text provided.
napi_get_and_clear_last_exception#
NAPI_EXTERN napi_status napi_get_and_clear_last_exception(napi_env env,
napi_value* result);
[in] env
: The environment that the API is invoked under.[out] result
: The exception if one is pending, NULL otherwise.
Returns napi_ok
if the API succeeded.
This API returns true if an exception is pending.
napi_is_exception_pending#
NAPI_EXTERN napi_status napi_is_exception_pending(napi_env env, bool* result);
[in] env
: The environment that the API is invoked under.[out] result
: Boolean value that is set to true if an exception is pending.
Returns napi_ok
if the API succeeded.
This API returns true if an exception is pending.
Fatal Errors#
In the event of an unrecoverable error in a native module, a fatal error can be thrown to immediately terminate the process.
napi_fatal_error#
NAPI_EXTERN NAPI_NO_RETURN void napi_fatal_error(const char* location, const char* message);
[in] location
: Optional location at which the error occurred.[in] message
: The message associated with the error.
The function call does not return, the process will be terminated.
Object Lifetime management#
As N-API calls are made, handles to objects in the heap for the underlying
VM may be returned as napi_values
. These handles must hold the
objects 'live' until they are no longer required by the native code,
otherwise the objects could be collected before the native code was
finished using them.
As object handles are returned they are associated with a 'scope'. The lifespan for the default scope is tied to the lifespan of the native method call. The result is that, by default, handles remain valid and the objects associated with these handles will be held live for the lifespan of the native method call.
In many cases, however, it is necessary that the handles remain valid for either a shorter or longer lifespan than that of the native method. The sections which follow describe the N-API functions than can be used to change the handle lifespan from the default.
Making handle lifespan shorter than that of the native method#
It is often necessary to make the lifespan of handles shorter than the lifespan of a native method. For example, consider a native method that has a loop which iterates through the elements in a large array:
for (int i = 0; i < 1000000; i++) {
napi_value result;
napi_status status = napi_get_element(e object, i, &result);
if (status != napi_ok) {
break;
}
// do something with element
}
This would result in a large number of handles being created, consuming substantial resources. In addition, even though the native code could only use the most recent handle, all of the associated objects would also be kept alive since they all share the same scope.
To handle this case, N-API provides the ability to establish a new 'scope' to
which newly created handles will be associated. Once those handles
are no longer required, the scope can be 'closed' and any handles associated
with the scope are invalidated. The methods available to open/close scopes are
napi_open_handle_scope
and napi_close_handle_scope
.
N-API only supports a single nested hiearchy of scopes. There is only one active scope at any time, and all new handles will be associated with that scope while it is active. Scopes must be closed in the reverse order from which they are opened. In addition, all scopes created within a native method must be closed before returning from that method.
Taking the earlier example, adding calls to napi_open_handle_scope
and
napi_close_handle_scope
would ensure that at most a single handle
is valid throughout the execution of the loop:
for (int i = 0; i < 1000000; i++) {
napi_handle_scope scope;
napi_status status = napi_open_handle_scope(env, &scope);
if (status != napi_ok) {
break;
}
napi_value result;
status = napi_get_element(e object, i, &result);
if (status != napi_ok) {
break;
}
// do something with element
status = napi_close_handle_scope(env, scope);
if (status != napi_ok) {
break;
}
}
When nesting scopes, there are cases where a handle from an inner scope needs to live beyond the lifespan of that scope. N-API supports an 'escapable scope' in order to support this case. An escapable scope allows one handle to be 'promoted' so that it 'escapes' the current scope and the lifespan of the handle changes from the current scope to that of the outer scope.
The methods available to open/close escapable scopes are
napi_open_escapable_handle_scope
and napi_close_escapable_handle_scope
.
The request to promote a handle is made through napi_escape_handle
which
can only be called once.
napi_open_handle_scope#
NODE_EXTERN napi_status napi_open_handle_scope(napi_env env,
napi_handle_scope* result);
[in] env
: The environment that the API is invoked under.[out] result
:napi_value
representing the new scope.
Returns napi_ok
if the API succeeded.
This API open a new scope.
napi_close_handle_scope#
NODE_EXTERN napi_status napi_close_handle_scope(napi_env env,
napi_handle_scope scope);
[in] env
: The environment that the API is invoked under.[in] scope
:napi_value
representing the scope to be closed.
Returns napi_ok
if the API succeeded.
This API closes the scope passed in. Scopes must be closed in the reverse order from which they were created.
napi_open_escapable_handle_scope#
NODE_EXTERN napi_status
napi_open_escapable_handle_scope(napi_env env,
napi_handle_scope* result);
[in] env
: The environment that the API is invoked under.[out] result
:napi_value
representing the new scope.
Returns napi_ok
if the API succeeded.
This API open a new scope from which one object can be promoted to the outer scope.
napi_close_escapable_handle_scope#
NODE_EXTERN napi_status
napi_close_escapable_handle_scope(napi_env env,
napi_handle_scope scope);
[in] env
: The environment that the API is invoked under.[in] scope
:napi_value
representing the scope to be closed.
Returns napi_ok
if the API succeeded.
This API closes the scope passed in. Scopes must be closed in the reverse order from which they were created.
napi_escape_handle#
NAPI_EXTERN napi_status napi_escape_handle(napi_env env,
napi_escapable_handle_scope scope,
napi_value escapee,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] scope
:napi_value
representing the current scope.[in] escapee
:napi_value
representing the JavaScript Object to be escaped.[out] result
:napi_value
representing the handle to the escaped Object in the outer scope.
Returns napi_ok
if the API succeeded.
This API promotes the handle to the JavaScript object so that it is valid for the lifetime of the outer scope. It can only be called once per scope. If it is called more than once an error will be returned.
References to objects with a lifespan longer than that of the native method#
In some cases an addon will need to be able to create and reference objects
with a lifespan longer than that of a single native method invocation. For
example, to create a constructor and later use that constructor
in a request to creates instances, it must be possible to reference
the constructor object across many different instance creation requests. This
would not be possible with a normal handle returned as a napi_value
as
described in the earlier section. The lifespan of a normal handle is
managed by scopes and all scopes must be closed before the end of a native
method.
N-API provides methods to create persistent references to an object. Each persistent reference has an associated count with a value of 0 or higher. The count determines if the reference will keep the corresponding object live. References with a count of 0 do not prevent the object from being collected and are often called 'weak' references. Any count greater than 0 will prevent the object from being collected.
References can be created with an initial reference count. The count can
then be modified through napi_reference_ref
and
napi_reference_unref
. If an object is collected while the count
for a reference is 0, all subsequent calls to
get the object associated with the reference napi_get_reference_value
will return NULL for the returned napi_value
. An attempt to call
napi_reference_ref
for a reference whose object has been collected
will result in an error.
References must be deleted once they are no longer required by the addon. When a reference is deleted it will no longer prevent the corresponding object from being collected. Failure to delete a persistent reference will result in a 'memory leak' with both the native memory for the persistent reference and the corresponding object on the heap being retained forever.
There can be multiple persistent references created which refer to the same object, each of which will either keep the object live or not based on its individual count.
napi_create_reference#
NODE_EXTERN napi_status napi_create_reference(napi_env env,
napi_value value,
int initial_refcount,
napi_ref* result);
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing the Object to which we want a reference to.[in] initial_refcount
: Initial reference count for the new reference.[out] result
:napi_ref
pointing to the new reference.
Returns napi_ok
if the API succeeded.
This API create a new reference with the specified reference count to the Object passed in.
napi_delete_reference#
NODE_EXTERN napi_status napi_delete_reference(napi_env env, napi_ref ref);
[in] env
: The environment that the API is invoked under.[in] ref
:napi_ref
to be deleted.
Returns napi_ok
if the API succeeded.
This API deletes the reference passed in.
napi_reference_ref#
NODE_EXTERN napi_status napi_reference_ref(napi_env env,
napi_ref ref,
int* result);
[in] env
: The environment that the API is invoked under.[in] ref
:napi_ref
for which the reference count will be incremented.[out] result
: The new reference count.
Returns napi_ok
if the API succeeded.
This API increments the reference count for the reference passed in and returns the resulting reference count.
napi_reference_unref#
NODE_EXTERN napi_status napi_reference_unref(napi_env env,
napi_ref ref,
int* result);
[in] env
: The environment that the API is invoked under.[in] ref
:napi_ref
for which the reference count will be decremented.[out] result
: The new reference count.
Returns napi_ok
if the API succeeded.
This API decrements the reference count for the reference passed in and returns the resulting reference count.
napi_get_reference_value#
NODE_EXTERN napi_status napi_get_reference_value(napi_env env,
napi_ref ref,
napi_value* result);
the napi_value passed
in or out of these methods is a handle to the
object to which the reference is related.
[in] env
: The environment that the API is invoked under.[in] ref
:napi_ref
for which we requesting the corresponding Object.[out] result
: Thenapi_value
for the Object referenced by thenapi_ref
.
Returns napi_ok
if the API succeeded.
If still valid, this API returns the napi_value
representing the
JavaScript Object associated with the napi_ref
. Otherise, result
will be NULL.
Module registration#
N-API modules are registered in the same manner as other modules
except that instead of using the NODE_MODULE
macro the following
is used:
NAPI_MODULE(addon, Init)
The next difference is the signature for the Init
method. For a N-API
module it is as follows:
void Init(napi_env env, napi_value exports, napi_value module, void* priv);
As with any other module, functions are exported by either adding them to
the exports
or module
objects passed to the Init
method.
For example, to add the method hello
as a function so that it can be called
as a method provided by the addon:
void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
napi_status status;
napi_property_descriptor desc =
{"hello", Method, 0, 0, 0, napi_default, 0};
status = napi_define_properties(env, exports, 1, &desc);
}
For example, to set a function to be returned by the require()
for the addon:
void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
napi_status status;
napi_property_descriptor desc =
{"exports", Method, 0, 0, 0, napi_default, 0};
status = napi_define_properties(env, module, 1, &desc);
}
For example, to define a class so that new instances can be created (often used with Object Wrap):
// NOTE: partial example, not all referenced code is included
napi_status status;
napi_property_descriptor properties[] = {
{ "value", nullptr, GetValue, SetValue, 0, napi_default, 0 },
DECLARE_NAPI_METHOD("plusOne", PlusOne),
DECLARE_NAPI_METHOD("multiply", Multiply),
};
napi_value cons;
status =
napi_define_class(env, "MyObject", New, nullptr, 3, properties, &cons);
if (status != napi_ok) return;
status = napi_create_reference(env, cons, 1, &constructor);
if (status != napi_ok) return;
status = napi_set_named_property(env, exports, "MyObject", cons);
if (status != napi_ok) return;
For more details on setting properties on either the exports
or module
objects, see the section on
Working with JavaScript Properties.
For more details on building addon modules in general, refer to the existing API
Working with JavaScript Values#
N-API exposes a set of APIs to create all types of JavaScript values. Some of these types are documented under Section 6 of the ECMAScript Language Specification.
Fundamentally, these APIs are used to do one of the following:
- Create a new JavaScript object
- Convert from a primitive C type to an N-API value
- Convert from N-API value to a primitive C type
- Get global instances including
undefined
andnull
N-API values are represented by the type napi_value
.
Any N-API call that requires a JavaScript value takes in a napi_value
.
In some cases, the API does check the type of the napi_value
up-front.
However, for better performance, it's better for the caller to make sure that
the napi_value
in question is of the JavaScript type expected by the API.
Enum types#
napi_valuetype#
typedef enum {
// ES6 types (corresponds to typeof)
napi_undefined,
napi_null,
napi_boolean,
napi_number,
napi_string,
napi_symbol,
napi_object,
napi_function,
napi_external,
} napi_valuetype;
Describes the type of a napi_value
. This generally corresponds to the types
described in
Section 6.1 of
the ECMAScript Language Specification.
In addition to types in that section, napi_valuetype
can also represent
Functions and Objects with external data.
napi_typedarray_type#
typedef enum {
napi_int8_array,
napi_uint8_array,
napi_uint8_clamped_array,
napi_int16_array,
napi_uint16_array,
napi_int32_array,
napi_uint32_array,
napi_float32_array,
napi_float64_array,
} napi_typedarray_type;
This represents the underlying binary scalar datatype of the TypedArray. Elements of this enum correspond to Section 22.2 of the ECMAScript Language Specification.
Object Creation Functions#
napi_create_array#
napi_status napi_create_array(napi_env env, napi_value* result)
[in] env
: The environment that the N-API call is invoked under.[out] result
: Anapi_value
representing a JavaScript Array.
Returns napi_ok
if the API succeeded.
This API returns an N-API value corresponding to a JavaScript Array type. JavaScript arrays are described in Section 22.1 of the ECMAScript Language Specification.
napi_create_array_with_length#
napi_status napi_create_array_with_length(napi_env env,
size_t length,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] length
: The initial length of the Array.[out] result
: Anapi_value
representing a JavaScript Array.
Returns napi_ok
if the API succeeded.
This API returns an N-API value corresponding to a JavaScript Array type.
The Array's length property is set to the passed-in length parameter.
However, the underlying buffer is not guaranteed to be pre-allocated by the VM
when the array is created - that behavior is left to the underlying VM
implementation.
If the buffer must be a contiguous block of memory that can be
directly read and/or written via C, consider using
napi_create_external_arraybuffer
.
JavaScript arrays are described in Section 22.1 of the ECMAScript Language Specification.
napi_create_arraybuffer#
napi_status napi_create_arraybuffer(napi_env env,
size_t byte_length,
void** data,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] length
: The length in bytes of the array buffer to create.[out] data
: Pointer to the underlying byte buffer of the ArrayBuffer.[out] result
: Anapi_value
representing a JavaScript ArrayBuffer.
Returns napi_ok
if the API succeeded.
This API returns an N-API value corresponding to a JavaScript ArrayBuffer.
ArrayBuffers are used to represent fixed-length binary data buffers. They are
normally used as a backing-buffer for TypedArray objects.
The ArrayBuffer allocated will have an underlying byte buffer whose size is
determined by the length
parameter that's passed in.
The underlying buffer is optionally returned back to the caller in case the
caller wants to directly manipulate the buffer. This buffer can only be
written to directly from native code. To write to this buffer from JavaScript,
a typed array or DataView object would need to be created.
JavaScript ArrayBuffer objects are described in Section 24.1 of the ECMAScript Language Specification.
napi_create_buffer#
napi_status napi_create_buffer(napi_env env,
size_t size,
void** data,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] size
: Size in bytes of the underlying buffer.[out] data
: Raw pointer to the underlying buffer.[out] result
: Anapi_value
representing anode::Buffer
.
Returns napi_ok
if the API succeeded.
This API allocates a node::Buffer
object. While this is still a
fully-supported data structure, in most cases using a TypedArray will suffice.
napi_create_buffer_copy#
napi_status napi_create_buffer_copy(napi_env env,
size_t length,
const void* data,
void** result_data,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] size
: Size in bytes of the input buffer (should be the same as the size of the new buffer).[in] data
: Raw pointer to the underlying buffer to copy from.[out] result_data
: Pointer to the new Buffer's underlying data buffer.[out] result
: Anapi_value
representing anode::Buffer
.
Returns napi_ok
if the API succeeded.
This API allocates a node::Buffer
object and initializes it with data copied
from the passed-in buffer. While this is still a fully-supported data
structure, in most cases using a TypedArray will suffice.
napi_create_external#
napi_status napi_create_external(napi_env env,
void* data,
napi_finalize finalize_cb,
void* finalize_hint,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] data
: Raw pointer to the external data.[in] finalize_cb
: Optional callback to call when the external value is being collected.[in] finalize_hint
: Optional hint to pass to the finalize callback during collection.[out] result
: Anapi_value
representing an external value.
Returns napi_ok
if the API succeeded.
This API allocates a JavaScript value with external data attached to it. This is used to pass external data through JavaScript code, so it can be retrieved later by native code. The API allows the caller to pass in a finalize callback, in case the underlying native resource needs to be cleaned up when the external JavaScript value gets collected.
Note: The created value is not an object, and therefore does not support
additional properties. It is considered a distinct value type: calling
napi_typeof()
with an external value yields napi_external
.
napi_create_external_arraybuffer#
napi_status
napi_create_external_arraybuffer(napi_env env,
void* external_data,
size_t byte_length,
napi_finalize finalize_cb,
void* finalize_hint,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] external_data
: Pointer to the underlying byte buffer of the ArrayBuffer.[in] byte_length
: The length in bytes of the underlying buffer.[in] finalize_cb
: Optional callback to call when the ArrayBuffer is being collected.[in] finalize_hint
: Optional hint to pass to the finalize callback during collection.[out] result
: Anapi_value
representing a JavaScript ArrayBuffer.
Returns napi_ok
if the API succeeded.
This API returns an N-API value corresponding to a JavaScript ArrayBuffer. The underlying byte buffer of the ArrayBuffer is externally allocated and managed. The caller must ensure that the byte buffer remains valid until the finalize callback is called.
JavaScript ArrayBuffers are described in Section 24.1 of the ECMAScript Language Specification.
napi_create_external_buffer#
napi_status napi_create_external_buffer(napi_env env,
size_t length,
void* data,
napi_finalize finalize_cb,
void* finalize_hint,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] length
: Size in bytes of the input buffer (should be the same as the size of the new buffer).[in] data
: Raw pointer to the underlying buffer to copy from.[in] finalize_cb
: Optional callback to call when the ArrayBuffer is being collected.[in] finalize_hint
: Optional hint to pass to the finalize callback during collection.[out] result
: Anapi_value
representing anode::Buffer
.
Returns napi_ok
if the API succeeded.
This API allocates a node::Buffer
object and initializes it with data
backed by the passed in buffer. While this is still a fully-supported data
structure, in most cases using a TypedArray will suffice.
Note: For Node.js >=4 Buffers
are Uint8Arrays.
napi_create_function#
napi_status napi_create_function(napi_env env,
const char* utf8name,
napi_callback cb,
void* data,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] utf8name
: A string representing the name of the function encoded as UTF8.[in] cb
: A function pointer to the native function to be invoked when the created function is invoked from JavaScript.[in] data
: Optional arbitrary context data to be passed into the native function when it is invoked.[out] result
: Anapi_value
representing a JavaScript function.
Returns napi_ok
if the API succeeded.
This API returns an N-API value corresponding to a JavaScript Function object. It's used to wrap native functions so that they can be invoked from JavaScript.
JavaScript Functions are described in Section 19.2 of the ECMAScript Language Specification.
napi_create_object#
napi_status napi_create_object(napi_env env, napi_value* result)
[in] env
: The environment that the API is invoked under.[out] result
: Anapi_value
representing a JavaScript Object.
Returns napi_ok
if the API succeeded.
This API allocates a default JavaScript Object.
It is the equivalent of doing new Object()
in JavaScript.
The JavaScript Object type is described in Section 6.1.7 of the ECMAScript Language Specification.
napi_create_symbol#
napi_status napi_create_symbol(napi_env env,
napi_value description,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] description
: Optional napi_value which refers to a JavaScript String to be set as the description for the symbol.[out] result
: Anapi_value
representing a JavaScript Symbol.
Returns napi_ok
if the API succeeded.
This API creates a JavaScript Symbol object from a UTF8-encoded C string
The JavaScript Symbol type is described in Section 19.4 of the ECMAScript Language Specification.
napi_create_typedarray#
napi_status napi_create_typedarray(napi_env env,
napi_typedarray_type type,
size_t length,
napi_value arraybuffer,
size_t byte_offset,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] type
: Scalar datatype of the elements within the TypedArray.[in] length
: Number of elements in the TypedArray.[in] arraybuffer
: ArrayBuffer underlying the typed array.[in] byte_offset
: The byte offset within the ArrayBuffer from which to start projecting the TypedArray.[out] result
: Anapi_value
representing a JavaScript TypedArray.
Returns napi_ok
if the API succeeded.
This API creates a JavaScript TypedArray object over an existing ArrayBuffer. TypedArray objects provide an array-like view over an underlying data buffer where each element has the same underlying binary scalar datatype.
It's required that (length * size_of_element) + byte_offset should be <= the size in bytes of the array passed in. If not, a RangeError exception is raised.
JavaScript TypedArray Objects are described in Section 22.2 of the ECMAScript Language Specification.
Functions to convert from C types to N-API#
napi_create_number#
napi_status napi_create_number(napi_env env, double value, napi_value* result)
[in] env
: The environment that the API is invoked under.[in] value
: Double-precision value to be represented in JavaScript.[out] result
: Anapi_value
representing a JavaScript Number.
Returns napi_ok
if the API succeeded.
This API is used to convert from the C double type to the JavaScript Number type.
The JavaScript Number type is described in Section 6.1.6 of the ECMAScript Language Specification.
napi_create_string_utf16#
napi_status napi_create_string_utf16(napi_env env,
const char16_t* str,
size_t length,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] str
: Character buffer representing a UTF16-LE-encoded string.[in] length
: The length of the string in two-byte code units, or -1 if it is null-terminated.[out] result
: Anapi_value
representing a JavaScript String.
Returns napi_ok
if the API succeeded.
This API creates a JavaScript String object from a UTF16-LE-encoded C string
The JavaScript String type is described in Section 6.1.4 of the ECMAScript Language Specification.
napi_create_string_latin1#
NAPI_EXTERN napi_status napi_create_string_latin1(napi_env env,
const char* str,
size_t length,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] str
: Character buffer representing a latin1-encoded string.[in] length
: The length of the string in bytes, or -1 if it is null-terminated.[out] result
: Anapi_value
representing a JavaScript String.
Returns napi_ok
if the API succeeded.
This API creates a JavaScript String object from a latin1-encoded C string.
The JavaScript String type is described in Section 6.1.4 of the ECMAScript Language Specification.
napi_create_string_utf8#
napi_status napi_create_string_utf8(napi_env env,
const char* str,
size_t length,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] str
: Character buffer representing a UTF8-encoded string.[in] length
: The length of the string in bytes, or -1 if it is null-terminated.[out] result
: Anapi_value
representing a JavaScript String.
Returns napi_ok
if the API succeeded.
This API creates a JavaScript String object from a UTF8-encoded C string
The JavaScript String type is described in Section 6.1.4 of the ECMAScript Language Specification.
Functions to convert from N-API to C types#
napi_get_array_length#
napi_status napi_get_array_length(napi_env env,
napi_value value,
uint32_t* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing the JavaScript Array whose length is being queried.[out] result
:uint32
representing length of the array.
Returns napi_ok
if the API succeeded.
This API returns the length of an array.
Array length is described in Section 22.1.4.1 of the ECMAScript Language Specification.
napi_get_arraybuffer_info#
napi_status napi_get_arraybuffer_info(napi_env env,
napi_value arraybuffer,
void** data,
size_t* byte_length)
[in] env
: The environment that the API is invoked under.[in] arraybuffer
:napi_value
representing the ArrayBuffer being queried.[out] data
: The underlying data buffer of the ArrayBuffer.[out] byte_length
: Length in bytes of the underlying data buffer.
Returns napi_ok
if the API succeeded.
This API is used to retrieve the underlying data buffer of an ArrayBuffer and its length.
WARNING: Use caution while using this API. The lifetime of the underlying data
buffer is managed by the ArrayBuffer even after it's returned. A
possible safe way to use this API is in conjunction with napi_create_reference
,
which can be used to guarantee control over the lifetime of the
ArrayBuffer. It's also safe to use the returned data buffer within the same
callback as long as there are no calls to other APIs that might trigger a GC.
napi_get_buffer_info#
napi_status napi_get_buffer_info(napi_env env,
napi_value value,
void** data,
size_t* length)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing thenode::Buffer
being queried.[out] data
: The underlying data buffer of thenode::Buffer
.[out] length
: Length in bytes of the underlying data buffer.
Returns napi_ok
if the API succeeded.
This API is used to retrieve the underlying data buffer of a node::Buffer
and it's length.
Warning: Use caution while using this API since the underlying data buffer's lifetime is not guaranteed if it's managed by the VM.
napi_get_prototype#
napi_status napi_get_prototype(napi_env env,
napi_value object,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] object
:napi_value
representing JavaScript Object whose prototype to return. This returns the equivalent ofObject.getPrototypeOf
(which is not the same as the function'sprototype
property).[out] result
:napi_value
representing prototype of the given object.
Returns napi_ok
if the API succeeded.
napi_get_typedarray_info#
napi_status napi_get_typedarray_info(napi_env env,
napi_value typedarray,
napi_typedarray_type* type,
size_t* length,
void** data,
napi_value* arraybuffer,
size_t* byte_offset)
[in] env
: The environment that the API is invoked under.[in] typedarray
:napi_value
representing the TypedArray whose properties to query.[out] type
: Scalar datatype of the elements within the TypedArray.[out] length
: Number of elements in the TypedArray.[out] data
: The data buffer underlying the typed array.[out] byte_offset
: The byte offset within the data buffer from which to start projecting the TypedArray.
Returns napi_ok
if the API succeeded.
This API returns various properties of a typed array.
Warning: Use caution while using this API since the underlying data buffer is managed by the VM
napi_get_value_bool#
napi_status napi_get_value_bool(napi_env env, napi_value value, bool* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript Boolean.[out] result
: C boolean primitive equivalent of the given JavaScript Boolean.
Returns napi_ok
if the API succeeded. If a non-boolean napi_value
is
passed in it returns napi_boolean_expected
.
This API returns the C boolean primitive equivalent of the given JavaScript Boolean.
napi_get_value_double#
napi_status napi_get_value_double(napi_env env,
napi_value value,
double* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript Number.[out] result
: C double primitive equivalent of the given JavaScript Number.
Returns napi_ok
if the API succeeded. If a non-number napi_value
is passed
in it returns napi_number_expected
.
This API returns the C double primitive equivalent of the given JavaScript Number.
napi_get_value_external#
napi_status napi_get_value_external(napi_env env,
napi_value value,
void** result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript external value.[out] result
: Pointer to the data wrapped by the JavaScript external value.
Returns napi_ok
if the API succeeded. If a non-external napi_value
is
passed in it returns napi_invalid_arg
.
This API retrieves the external data pointer that was previously passed to
napi_create_external()
.
napi_get_value_int32#
napi_status napi_get_value_int32(napi_env env,
napi_value value,
int32_t* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript Number.[out] result
: C int32 primitive equivalent of the given JavaScript Number.
Returns napi_ok
if the API succeeded. If a non-number napi_value
is passed in `napi_number_expected .
This API returns the C int32 primitive equivalent of the given JavaScript Number. If the number exceeds the range of the 32 bit integer, then the result is truncated to the equivalent of the bottom 32 bits. This can result in a large positive number becoming a negative number if the the value is > 2^31 -1.
napi_get_value_int64#
napi_status napi_get_value_int64(napi_env env,
napi_value value,
int64_t* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript Number.[out] result
: C int64 primitive equivalent of the given JavaScript Number.
Returns napi_ok
if the API succeeded. If a non-number napi_value
is passed in it returns napi_number_expected
.
This API returns the C int64 primitive equivalent of the given JavaScript Number
napi_get_value_string_utf8#
napi_status napi_get_value_string_utf8(napi_env env,
napi_value value,
char* buf,
size_t bufsize,
size_t* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript string.[in] buf
: Buffer to write the UTF8-encoded string into. If NULL is passed in, the length of the string (in bytes) is returned.[in] bufsize
: Size of the destination buffer.[out] result
: Number of bytes copied into the buffer including the null. terminator. If the buffer size is insufficient, the string will be truncated including a null terminator.
Returns napi_ok
if the API succeeded. Ifa non-String napi_value
x is passed in it returns napi_string_expected
.
This API returns the UTF8-encoded string corresponding the value passed in.
napi_get_value_string_utf16#
napi_status napi_get_value_string_utf16(napi_env env,
napi_value value,
char16_t* buf,
size_t bufsize,
size_t* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript string.[in] buf
: Buffer to write the UTF16-LE-encoded string into. If NULL is passed in, the length of the string (in 2-byte code units) is returned.[in] bufsize
: Size of the destination buffer.[out] result
: Number of 2-byte code units copied into the buffer including the null terminateor. If the buffer size is insufficient, the string will be truncated including a null terminator.
Returns napi_ok
if the API succeeded. If a non-String napi_value
is passed in it returns napi_string_expected
.
This API returns the UTF16-encoded string corresponding the value passed in.
napi_get_value_uint32#
napi_status napi_get_value_uint32(napi_env env,
napi_value value,
uint32_t* result)
[in] env
: The environment that the API is invoked under.[in] value
:napi_value
representing JavaScript Number.[out] result
: C primitive equivalent of the givennapi_value
as auint32_t
.
Returns napi_ok
if the API succeeded. If a non-number napi_value
is passed in it returns napi_number_expected
.
This API returns the C primitive equivalent of the given napi_value
as a
uint32_t
.
Functions to get global instances#
napi_get_boolean#
napi_status napi_get_boolean(napi_env env, bool value, napi_value* result)
[in] env
: The environment that the API is invoked under.[in] value
: The value of the boolean to retrieve.[out] result
:napi_value
representing JavaScript Boolean singleton to retrieve.
Returns napi_ok
if the API succeeded.
This API is used to return the JavaScript singleton object that is used to represent the given boolean value
napi_get_global#
napi_status napi_get_global(napi_env env, napi_value* result)
[in] env
: The environment that the API is invoked under.[out] result
:napi_value
representing JavaScript Global Object.
Returns napi_ok
if the API succeeded.
This API returns the global Object.
napi_get_null#
napi_status napi_get_null(napi_env env, napi_value* result)
[in] env
: The environment that the API is invoked under.[out] result
:napi_value
representing JavaScript Null Object.
Returns napi_ok
if the API succeeded.
This API returns the null Object.
napi_get_undefined#
napi_status napi_get_undefined(napi_env env, napi_value* result)
[in] env
: The environment that the API is invoked under.[out] result
:napi_value
representing JavaScript Undefined value.
Returns napi_ok
if the API succeeded.
This API returns the Undefined object.
Working with JavaScript Values - Abstract Operations#
N-API exposes a set of APIs to perform some abstract operations on JavaScript values. Some of these operations are documented under Section 7 of the ECMAScript Language Specification.
These APIs support doing one of the following:
- Coerce JavaScript values to specific JavaScript types (such as Number or String)
- Check the type of a JavaScript value
- Check for equality between two JavaScript values
napi_coerce_to_bool#
napi_status napi_coerce_to_bool(napi_env env,
napi_value value,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to coerce.[out] result
:napi_value
representing the coerced JavaScript Boolean.
Returns napi_ok
if the API succeeded.
This API implements the abstract operation ToBoolean as defined in Section 7.1.2 of the ECMAScript Language Specification. This API can be re-entrant if getters are defined on the passed-in Object.
napi_coerce_to_number#
napi_status napi_coerce_to_number(napi_env env,
napi_value value,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to coerce.[out] result
:napi_value
representing the coerced JavaScript Number.
Returns napi_ok
if the API succeeded.
This API implements the abstract operation ToNumber as defined in Section 7.1.3 of the ECMAScript Language Specification. This API can be re-entrant if getters are defined on the passed-in Object.
napi_coerce_to_object#
napi_status napi_coerce_to_object(napi_env env,
napi_value value,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to coerce.[out] result
:napi_value
representing the coerced JavaScript Object.
Returns napi_ok
if the API succeeded.
This API implements the abstract operation ToObject as defined in Section 7.1.13 of the ECMAScript Language Specification. This API can be re-entrant if getters are defined on the passed-in Object.
napi_coerce_to_string#
napi_status napi_coerce_to_string(napi_env env,
napi_value value,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to coerce.[out] result
:napi_value
representing the coerced JavaScript String.
Returns napi_ok
if the API succeeded.
This API implements the abstract operation ToString as defined in Section 7.1.13 of the ECMAScript Language Specification. This API can be re-entrant if getters are defined on the passed-in Object.
napi_typeof#
napi_status napi_typeof(napi_env env, napi_value value, napi_valuetype* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value whose type to query.[out] result
: The type of the JavaScript value.
Returns napi_ok
if the API succeeded.
napi_invalid_arg
if the type ofvalue
is not a known ECMAScript type andvalue
is not an External value.
This API represents behavior similar to invoking the typeof
Operator on
the object as defined in Section 12.5.5 of the ECMAScript Language
Specification. However, it has support for detecting an External value.
If value
has a type that is invalid, an error is returned.
napi_instanceof#
napi_status napi_instanceof(napi_env env,
napi_value object,
napi_value constructor,
bool* result)
[in] env
: The environment that the API is invoked under.[in] object
: The JavaScript value to check.[in] constructor
: The JavaScript function object of the constructor function to check against.[out] result
: Boolean that is set to true ifobject instanceof constructor
is true.
Returns napi_ok
if the API succeeded.
This API represents invoking the instanceof
Operator on the object as
defined in
Section 12.10.4
of the ECMAScript Language Specification.
napi_is_array#
napi_status napi_is_array(napi_env env, napi_value value, bool* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to check.[out] result
: Whether the given object is an array.
Returns napi_ok
if the API succeeded.
This API represents invoking the IsArray
operation on the object
as defined in Section 7.2.2
of the ECMAScript Language Specification.
napi_is_arraybuffer#
napi_status napi_is_arraybuffer(napi_env env, napi_value value, bool* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to check.[out] result
: Whether the given object is an ArrayBuffer.
Returns napi_ok
if the API succeeded.
This API checks if the Object passsed in is an array buffer.
napi_is_buffer#
napi_status napi_is_buffer(napi_env env, napi_value value, bool* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to check.[out] result
: Whether the givennapi_value
represents anode::Buffer
object.
Returns napi_ok
if the API succeeded.
This API checks if the Object passsed in is a buffer.
napi_is_error#
napi_status napi_is_error(napi_env env, napi_value value, bool* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to check.[out] result
: Whether the givennapi_value
represents an Error object.
Returns napi_ok
if the API succeeded.
This API checks if the Object passsed in is an Error.
napi_is_typedarray#
napi_status napi_is_typedarray(napi_env env, napi_value value, bool* result)
[in] env
: The environment that the API is invoked under.[in] value
: The JavaScript value to check.[out] result
: Whether the givennapi_value
represents a TypedArray.
Returns napi_ok
if the API succeeded.
This API checks if the Object passsed in is a typed array.
napi_strict_equals#
napi_status napi_strict_equals(napi_env env,
napi_value lhs,
napi_value rhs,
bool* result)
[in] env
: The environment that the API is invoked under.[in] lhs
: The JavaScript value to check.[in] rhs
: The JavaScript value to check against.[out] result
: Whether the twonapi_value
objects are equal.
Returns napi_ok
if the API succeeded.
This API represents the invocation of the Strict Equality algorithm as defined in Section 7.2.14 of the ECMAScript Language Specification.
Working with JavaScript Properties#
N-API exposes a set of APIs to get and set properties on JavaScript objects. Some of these types are documented under Section 7 of the ECMAScript Language Specification.
Properties in JavaScript are represented as a tuple of a key and a value. Fundamentally, all property keys in N-API can be represented in one of the following forms:
- Named: a simple UTF8-encoded string
- Integer-Indexed: an index value represented by
uint32_t
- JavaScript value: these are represented in N-API by
napi_value
. This can be anapi_value
representing a String, Number or Symbol.
N-API values are represented by the type napi_value
.
Any N-API call that requires a JavaScript value takes in a napi_value
.
However, it's the caller's responsibility to make sure that the
napi_value
in question is of the JavaScript type expected by the API.
The APIs documented in this section provide a simple interface to
get and set properties on arbitrary JavaScript objects represented by
napi_value
.
For instance, consider the following JavaScript code snippet:
const obj = {};
obj.myProp = 123;
The equivalent can be done using N-API values with the following snippet:
napi_status status = napi_generic_failure;
// const obj = {}
napi_value obj, value;
status = napi_create_object(env, &obj);
if (status != napi_ok) return status;
// Create a napi_value for 123
status = napi_create_number(env, 123, &value);
if (status != napi_ok) return status;
// obj.myProp = 123
status = napi_set_named_property(env, obj, "myProp", value);
if (status != napi_ok) return status;
Indexed properties can be set in a similar manner. Consider the following JavaScript snippet:
const arr = [];
arr[123] = 'hello';
The equivalent can be done using N-API values with the following snippet:
napi_status status = napi_generic_failure;
// const arr = [];
napi_value arr, value;
status = napi_create_array(env, &arr);
if (status != napi_ok) return status;
// Create a napi_value for 'hello'
status = napi_create_string_utf8(env, "hello", -1, &value);
if (status != napi_ok) return status;
// arr[123] = 'hello';
status = napi_set_element(env, arr, 123, value);
if (status != napi_ok) return status;
Properties can be retrieved using the APIs described in this section. Consider the following JavaScript snippet:
const arr = [];
const value = arr[123];
The following is the approximate equivalent of the N-API counterpart:
napi_status status = napi_generic_failure;
// const arr = []
napi_value arr, value;
status = napi_create_array(env, &arr);
if (status != napi_ok) return status;
// const value = arr[123]
status = napi_get_element(env, arr, 123, &value);
if (status != napi_ok) return status;
Finally, multiple properties can also be defined on an object for performance reasons. Consider the following JavaScript:
const obj = {};
Object.defineProperties(obj, {
'foo': { value: 123, writable: true, configurable: true, enumerable: true },
'bar': { value: 456, writable: true, configurable: true, enumerable: true }
});
The following is the approximate equivalent of the N-API counterpart:
napi_status status = napi_status_generic_failure;
// const obj = {};
napi_value obj;
status = napi_create_obj(env, &obj);
if (status != napi_ok) return status;
// Create napi_values for 123 and 456
napi_value fooValue, barValue;
status = napi_create_number(env, 123, &fooValue);
if (status != napi_ok) return status;
status = napi_create_number(env, 456, &barValue);
if (status != napi_ok) return status;
// Set the properties
napi_property_descriptors descriptors[] = {
{ "foo", fooValue, 0, 0, 0, napi_default, 0 },
{ "bar", barValue, 0, 0, 0, napi_default, 0 }
}
status = napi_define_properties(env,
obj,
sizeof(descriptors) / sizeof(descriptors[0]),
descriptors);
if (status != napi_ok) return status;
Structures#
napi_property_attributes#
typedef enum {
napi_default = 0,
napi_writable = 1 << 0,
napi_enumerable = 1 << 1,
napi_configurable = 1 << 2,
// Used with napi_define_class to distinguish static properties
// from instance properties. Ignored by napi_define_properties.
napi_static = 1 << 10,
} napi_property_attributes;
napi_property_attributes
are flags used to control the behavior of properties
set on a JavaScript object. Other than napi_static
they correspond to the
attributes listed in Section 6.1.7.1
of the ECMAScript Language Specification.
They can be one or more of the following bitflags:
napi_default
- Used to indicate that no explicit attributes are set on the given property. By default, a property is read only, not enumerable and not configurable.napi_writable
- Used to indicate that a given property is writable.napi_enumerable
- Used to indicate that a given property is enumerable.napi_configurable
- Used to indicate that a given property is configurable, as defined in Section 6.1.7.1 of the ECMAScript Language Specification.napi_static
- Used to indicate that the property will be defined as a static property on a class as opposed to an instance property, which is the default. This is used only bynapi_define_class
. It is ignored bynapi_define_properties
.
napi_property_descriptor#
typedef struct {
// One of utf8name or name should be NULL.
const char* utf8name;
napi_value name;
napi_callback method;
napi_callback getter;
napi_callback setter;
napi_value value;
napi_property_attributes attributes;
void* data;
} napi_property_descriptor;
utf8name
: Optional String describing the key for the property, encoded as UTF8. One ofutf8name
orname
must be provided for the property.name
: Optional napi_value that points to a JavaScript string or symbol to be used as the key for the property. One ofutf8name
orname
must be provided for the property.value
: The value that's retrieved by a get access of the property if the property is a data property. If this is passed in, setgetter
,setter
,method
anddata
toNULL
(since these members won't be used).getter
: A function to call when a get access of the property is performed. If this is passed in, setvalue
andmethod
toNULL
(since these members won't be used). The given function is called implicitly by the runtime when the property is accessed from JavaScript code (or if a get on the property is performed using a N-API call).setter
: A function to call when a set access of the property is performed. If this is passed in, setvalue
andmethod
toNULL
(since these members won't be used). The given function is called implicitly by the runtime when the property is set from JavaScript code (or if a set on the property is performed using a N-API call).method
: Set this to make the property descriptor object'svalue
property to be a JavaScript function represented bymethod
. If this is passed in, setvalue
,getter
andsetter
toNULL
(since these members won't be used).data
: The callback data passed intomethod
,getter
andsetter
if this function is invoked.attributes
: The attributes associated with the particular property. Seenapi_property_attributes
.
Functions#
napi_get_property_names#
napi_status napi_get_property_names(napi_env env,
napi_value object,
napi_value* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object from which to retrieve the properties.[out] result
: Anapi_value
representing an array of JavaScript values that represent the property names of the object. The API can be used to iterate overresult
usingnapi_get_array_length
andnapi_get_element
.
Returns napi_ok
if the API succeeded.
This API returns the array of propertys for the Object passed in
napi_set_property#
napi_status napi_set_property(napi_env env,
napi_value object,
napi_value key,
napi_value value);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object on which to set the property.[in] key
: The name of the property to set.[in] value
: The property value.
Returns napi_ok
if the API succeeded.
This API set a property on the Object passed in.
napi_get_property#
napi_status napi_get_property(napi_env env,
napi_value object,
napi_value key,
napi_value* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object from which to retrieve the property.[in] key
: The name of the property to retrieve.[out] result
: The value of the property.
Returns napi_ok
if the API succeeded.
This API gets the requested property from the Object passed in.
napi_has_property#
napi_status napi_has_property(napi_env env,
napi_value object,
napi_value key,
bool* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object to query.[in] key
: The name of the property whose existence to check.[out] result
: Whether the property exists on the object or not.
Returns napi_ok
if the API succeeded.
This API checks if the Object passed in has the named property.
napi_delete_property#
napi_status napi_delete_property(napi_env env,
napi_value object,
napi_value key,
bool* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object to query.[in] key
: The name of the property to delete.[out] result
: Whether the property deletion succeeded or not.result
can optionally be ignored by passingNULL
.
Returns napi_ok
if the API succeeded.
This API attempts to delete the key
own property from object
.
napi_has_own_property#
napi_status napi_has_own_property(napi_env env,
napi_value object,
napi_value key,
bool* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object to query.[in] key
: The name of the own property whose existence to check.[out] result
: Whether the own property exists on the object or not.
Returns napi_ok
if the API succeeded.
This API checks if the Object passed in has the named own property. key
must
be a string or a Symbol, or an error will be thrown. N-API will not perform any
conversion between data types.
napi_set_named_property#
napi_status napi_set_named_property(napi_env env,
napi_value object,
const char* utf8Name,
napi_value value);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object on which to set the property.[in] utf8Name
: The name of the property to set.[in] value
: The property value.
Returns napi_ok
if the API succeeded.
This method is equivalent to calling napi_set_property
with a napi_value
created from the string passed in as utf8Name
napi_get_named_property#
napi_status napi_get_named_property(napi_env env,
napi_value object,
const char* utf8Name,
napi_value* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object from which to retrieve the property.[in] utf8Name
: The name of the property to get.[out] result
: The value of the property.
Returns napi_ok
if the API succeeded.
This method is equivalent to calling napi_get_property
with a napi_value
created from the string passed in as utf8Name
napi_has_named_property#
napi_status napi_has_named_property(napi_env env,
napi_value object,
const char* utf8Name,
bool* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object to query.[in] utf8Name
: The name of the property whose existence to check.[out] result
: Whether the property exists on the object or not.
Returns napi_ok
if the API succeeded.
This method is equivalent to calling napi_has_property
with a napi_value
created from the string passed in as utf8Name
napi_set_element#
napi_status napi_set_element(napi_env env,
napi_value object,
uint32_t index,
napi_value value);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object from which to set the properties.[in] index
: The index of the property to set.[in] value
: The property value.
Returns napi_ok
if the API succeeded.
This API sets and element on the Object passed in.
napi_get_element#
napi_status napi_get_element(napi_env env,
napi_value object,
uint32_t index,
napi_value* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object from which to retrieve the property.[in] index
: The index of the property to get.[out] result
: The value of the property.
Returns napi_ok
if the API succeeded.
This API gets the element at the requested index.
napi_has_element#
napi_status napi_has_element(napi_env env,
napi_value object,
uint32_t index,
bool* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object to query.[in] index
: The index of the property whose existence to check.[out] result
: Whether the property exists on the object or not.
Returns napi_ok
if the API succeeded.
This API returns if the Object passed in has an element at the requested index.
napi_delete_element#
napi_status napi_delete_element(napi_env env,
napi_value object,
uint32_t index,
bool* result);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object to query.[in] index
: The index of the property to delete.[out] result
: Whether the element deletion succeeded or not.result
can optionally be ignored by passingNULL
.
Returns napi_ok
if the API succeeded.
This API attempts to delete the specified index
from object
.
napi_define_properties#
napi_status napi_define_properties(napi_env env,
napi_value object,
size_t property_count,
const napi_property_descriptor* properties);
[in] env
: The environment that the N-API call is invoked under.[in] object
: The object from which to retrieve the properties.[in] property_count
: The number of elements in theproperties
array.[in] properties
: The array of property descriptors.
Returns napi_ok
if the API succeeded.
This method allows the efficient definition of multiple properties on a given
object. The properties are defined using property descriptors (See
napi_property_descriptor
). Given an array of such property descriptors, this
API will set the properties on the object one at a time, as defined by
DefineOwnProperty (described in Section 9.1.6 of the ECMA262 specification).
Working with JavaScript Functions#
N-API provides a set of APIs that allow JavaScript code to
call back into native code. N-API APIs that support calling back
into native code take in a callback functions represented by
the napi_callback
type. When the JavaScript VM calls back to
native code, the napi_callback
function provided is invoked. The APIs
documented in this section allow the callback function to do the
following:
- Get information about the context in which the callback was invoked.
- Get the arguments passed into the callback.
- Return a
napi_value
back from the callback.
Additionally, N-API provides a set of functions which allow calling JavaScript functions from native code. One can either call a function like a regular JavaScript function call, or as a constructor function.
napi_call_function#
napi_status napi_call_function(napi_env env,
napi_value recv,
napi_value func,
int argc,
const napi_value* argv,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] recv
: Thethis
object passed to the called function.[in] func
:napi_value
representing the JavaScript function to be invoked.[in] argc
: The count of elements in theargv
array.[in] argv
: Array ofnapi_values
representing JavaScript values passed in as arguments to the function.[out] result
:napi_value
representing the JavaScript object returned.
Returns napi_ok
if the API succeeded.
This method allows a JavaScript function object to be called from a native
add-on. This is an primary mechanism of calling back from the add-on's
native code into JavaScript. For special cases like calling into JavaScript
after an async operation, see napi_make_callback
.
A sample use case might look as follows. Consider the following JavaScript snippet:
function AddTwo(num) {
return num + 2;
}
Then, the above function can be invoked from a native add-on using the following code:
// Get the function named "AddTwo" on the global object
napi_value global, add_two, arg;
napi_status status = napi_get_global(env, &global);
if (status != napi_ok) return;
status = napi_get_named_property(env, global, "AddTwo", &add_two);
if (status != napi_ok) return;
// const arg = 1337
status = napi_create_number(env, 1337, &arg);
if (status != napi_ok) return;
napi_value* argv = &arg;
size_t argc = 1;
// AddTwo(arg);
napi_value return_val;
status = napi_call_function(env, global, add_two, argc, argv, &return_val);
if (status != napi_ok) return;
// Convert the result back to a native type
int32_t result;
status = napi_get_value_int32(env, return_val, &result);
if (status != napi_ok) return;
napi_create_function#
napi_status napi_create_function(napi_env env,
const char* utf8name,
napi_callback cb,
void* data,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] utf8Name
: The name of the function encoded as UTF8. This is visible within JavaScript as the new function object'sname
property.[in] cb
: The native function which should be called when this function object is invoked.[in] data
: User-provided data context. This will be passed back into the function when invoked later.[out] result
:napi_value
representing the JavaScript function object for the newly created function.
Returns napi_ok
if the API succeeded.
This API allows an add-on author to create a function object in native code. This is the primary mechanism to allow calling into the add-on's native code from Javascript.
Note: The newly created function is not automatically visible from script after this call. Instead, a property must be explicitly set on any object that is visible to JavaScript, in order for the function to be accessible from script.
In order to expose a function as part of the add-on's module exports, set the newly created function on the exports object. A sample module might look as follows:
napi_value SayHello(napi_env env, napi_callback_info info) {
printf("Hello\n");
return nullptr;
}
void Init(napi_env env, napi_value exports, napi_value module, void* priv) {
napi_status status;
napi_value fn;
status = napi_create_function(env, NULL, SayHello, NULL, &fn);
if (status != napi_ok) return;
status = napi_set_named_property(env, exports, "sayHello", fn);
if (status != napi_ok) return;
}
NAPI_MODULE(addon, Init)
Given the above code, the add-on can be used from JavaScript as follows:
const myaddon = require('./addon');
myaddon.sayHello();
Note: The string passed to require is not necessarily the name passed into
NAPI_MODULE
in the earlier snippet but the name of the target in binding.gyp
responsible for creating the .node
file.
napi_get_cb_info#
napi_status napi_get_cb_info(napi_env env,
napi_callback_info cbinfo,
size_t* argc,
napi_value* argv,
napi_value* thisArg,
void** data)
[in] env
: The environment that the API is invoked under.[in] cbinfo
: The callback info passed into the callback function.[in-out] argc
: Specifies the size of the providedargv
array and receives the actual count of arguments.[out] argv
: Buffer to which thenapi_value
representing the arguments are copied. If there are more arguments than the provided count, only the requested number of arguments are copied. If there are fewer arguments provided than claimed, the rest ofargv
is filled withnapi_value
values that representundefined
.[out] this
: Receives the JavaScriptthis
argument for the call.[out] data
: Receives the data pointer for the callback.
Returns napi_ok
if the API succeeded.
This method is used within a callback function to retrieve details about the
call like the arguments and the this
pointer from a given callback info.
napi_is_construct_call#
napi_status napi_is_construct_call(napi_env env,
napi_callback_info cbinfo,
bool* result)
[in] env
: The environment that the API is invoked under.[in] cbinfo
: The callback info passed into the callback function.[out] result
: Whether the native function is being invoked as a constructor call.
Returns napi_ok
if the API succeeded.
This API checks if the the current callback was due to a consructor call.
napi_new_instance#
napi_status napi_new_instance(napi_env env,
napi_value cons,
size_t argc,
napi_value* argv,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] cons
:napi_value
representing the JavaScript function to be invoked as a constructor.[in] argc
: The count of elements in theargv
array.[in] argv
: Array of JavaScript values asnapi_value
representing the arguments to the constructor.[out] result
:napi_value
representing the JavaScript object returned, which in this case is the constructed object.
This method is used to instantiate a new JavaScript value using a given
napi_value
that represents the constructor for the object. For example,
consider the following snippet:
function MyObject(param) {
this.param = param;
}
const arg = 'hello';
const value = new MyObject(arg);
The following can be approximated in N-API using the following snippet:
// Get the constructor function MyObject
napi_value global, constructor, arg, value;
napi_status status = napi_get_global(env, &global);
if (status != napi_ok) return;
status = napi_get_named_property(env, global, "MyObject", &constructor);
if (status != napi_ok) return;
// const arg = "hello"
status = napi_create_string_utf8(env, "hello", -1, &arg);
if (status != napi_ok) return;
napi_value* argv = &arg;
size_t argc = 1;
// const value = new MyObject(arg)
status = napi_new_instance(env, constructor, argc, argv, &value);
Returns napi_ok
if the API succeeded.
napi_make_callback#
napi_status napi_make_callback(napi_env env,
napi_value recv,
napi_value func,
int argc,
const napi_value* argv,
napi_value* result)
[in] env
: The environment that the API is invoked under.[in] recv
: Thethis
object passed to the called function.[in] func
:napi_value
representing the JavaScript function to be invoked.[in] argc
: The count of elements in theargv
array.[in] argv
: Array of JavaScript values asnapi_value
representing the arguments to the function.[out] result
:napi_value
representing the JavaScript object returned.
Returns napi_ok
if the API succeeded.
This method allows a JavaScript function object to be called from a native
add-on. This API is similar to napi_call_function
. However, it is used to call
from native code back into JavaScript after returning from an async
operation (when there is no other script on the stack). It is a fairly simple
wrapper around node::MakeCallback
.
For an example on how to use napi_make_callback
, see the section on
Asynchronous Operations.
Object Wrap#
N-API offers a way to "wrap" C++ classes and instances so that the class constructor and methods can be called from JavaScript.
- The
napi_define_class
API defines a JavaScript class with constructor, static properties and methods, and instance properties and methods that correspond to the The C++ class. - When JavaScript code invokes the constructor, the constructor callback
uses
napi_wrap
to wrap a new C++ instance in a JavaScript object, then returns the wrapper object. - When JavaScript code invokes a method or property accessor on the class,
the corresponding
napi_callback
C++ function is invoked. For an instance callback,napi_unwrap
obtains the C++ instance that is the target of the call.
napi_define_class#
napi_status napi_define_class(napi_env env,
const char* utf8name,
napi_callback constructor,
void* data,
size_t property_count,
const napi_property_descriptor* properties,
napi_value* result);
[in] env
: The environment that the API is invoked under.[in] utf8name
: Name of the JavaScript constructor function; this is not required to be the same as the C++ class name, though it is recommended for clarity.[in] constructor
: Callback function that handles constructing instances of the class. (This should be a static method on the class, not an actual C++ constructor function.)[in] data
: Optional data to be passed to the constructor callback as thedata
property of the callback info.[in] property_count
: Number of items in theproperties
array argument.[in] properties
: Array of property descriptors describing static and instance data properties, accessors, and methods on the class Seenapi_property_descriptor
.[out] result
: Anapi_value
representing the constructor function for the class.
Returns napi_ok
if the API succeeded.
Defines a JavaScript class that corresponds to a C++ class, including:
- A JavaScript constructor function that has the class name and invokes the provided C++ constructor callback.
- Properties on the constructor function corresponding to static data
properties, accessors, and methods of the C++ class (defined by
property descriptors with the
napi_static
attribute). - Properties on the constructor function's
prototype
object corresponding to non-static data properties, accessors, and methods of the C++ class (defined by property descriptors without thenapi_static
attribute).
The C++ constructor callback should be a static method on the class that calls
the actual class constructor, then wraps the new C++ instance in a JavaScript
object, and returns the wrapper object. See napi_wrap()
for details.
The JavaScript constructor function returned from napi_define_class
is
often saved and used later, to construct new instances of the class from native
code, and/or check whether provided values are instances of the class. In that
case, to prevent the function value from being garbage-collected, create a
persistent reference to it using napi_create_reference
and ensure the
reference count is kept >= 1.
napi_wrap#
napi_status napi_wrap(napi_env env,
napi_value js_object,
void* native_object,
napi_finalize finalize_cb,
void* finalize_hint,
napi_ref* result);
[in] env
: The environment that the API is invoked under.[in] js_object
: The JavaScript object that will be the wrapper for the native object. This object must have been created from theprototype
of a constructor that was created usingnapi_define_class()
.[in] native_object
: The native instance that will be wrapped in the JavaScript object.[in] finalize_cb
: Optional native callback that can be used to free the native instance when the JavaScript object is ready for garbage-collection.[in] finalize_hint
: Optional contextual hint that is passed to the finalize callback.[out] result
: Optional reference to the wrapped object.
Returns napi_ok
if the API succeeded.
Wraps a native instance in a JavaScript object. The native instance can be
retrieved later using napi_unwrap()
.
When JavaScript code invokes a constructor for a class that was defined using
napi_define_class()
, the napi_callback
for the constructor is invoked.
After constructing an instance of the native class, the callback must then call
napi_wrap()
to wrap the newly constructed instance in the already-created
JavaScript object that is the this
argument to the constructor callback.
(That this
object was created from the constructor function's prototype
,
so it already has definitions of all the instance properties and methods.)
Typically when wrapping a class instance, a finalize callback should be
provided that simply deletes the native instance that is received as the data
argument to the finalize callback.
The optional returned reference is initially a weak reference, meaning it has a reference count of 0. Typically this reference count would be incremented temporarily during async operations that require the instance to remain valid.
Caution: The optional returned reference (if obtained) should be deleted via
napi_delete_reference
ONLY in response to the finalize callback
invocation. (If it is deleted before then, then the finalize callback may never
be invoked.) Therefore, when obtaining a reference a finalize callback is also
required in order to enable correct proper of the reference.
Note: This API may modify the prototype chain of the wrapper object.
Afterward, additional manipulation of the wrapper's prototype chain may cause
napi_unwrap()
to fail.
Note: Calling napi_wrap()
a second time on an object that already has a
native instance associated with it by virtue of a previous call to
napi_wrap()
will cause an error to be returned.
napi_unwrap#
napi_status napi_unwrap(napi_env env,
napi_value js_object,
void** result);
[in] env
: The environment that the API is invoked under.[in] js_object
: The object associated with the C++ class instance.[out] result
: Pointer to the wrapped C++ class instance.
Returns napi_ok
if the API succeeded.
Retrieves a native instance that was previously wrapped in a JavaScript
object using napi_wrap()
.
When JavaScript code invokes a method or property accessor on the class, the
corresponding napi_callback
is invoked. If the callback is for an instance
method or accessor, then the this
argument to the callback is the wrapper
object; the wrapped C++ instance that is the target of the call can be obtained
then by calling napi_unwrap()
on the wrapper object.
Asynchronous Operations#
Addon modules often need to leverage async helpers from libuv as part of their implementation. This allows them to schedule work to be executed asynchronously so that their methods can return in advance of the work being completed. This is important in order to allow them to avoid blocking overall execution of the Node.js application.
N-API provides an ABI-stable interface for these supporting functions which covers the most common asynchronous use cases.
N-API defines the napi_work
structure which is used to manage
asynchronous workers. Instances are created/deleted with
napi_create_async_work
and napi_delete_async_work
.
The execute
and complete
callbacks are functions that will be
invoked when the executor is ready to execute and when it completes its
task respectively. These functions implement the following interfaces:
typedef void (*napi_async_execute_callback)(napi_env env,
void* data);
typedef void (*napi_async_complete_callback)(napi_env env,
napi_status status,
void* data);
When these methods are invoked, the data
parameter passed will be the
addon-provided void* data that was passed into the
napi_create_async_work
call.
Once created the async worker can be queued
for execution using the napi_queue_async_work
function:
NAPI_EXTERN napi_status napi_queue_async_work(napi_env env,
napi_async_work work);
napi_cancel_async_work
can be used if the work needs
to be cancelled before the work has started execution.
After calling napi_cancel_async_work
, the complete
callback
will be invoked with a status value of napi_cancelled
.
The work should not be deleted before the complete
callback invocation, even when it was cancelled.
napi_create_async_work#
NAPI_EXTERN
napi_status napi_create_async_work(napi_env env,
napi_async_execute_callback execute,
napi_async_complete_callback complete,
void* data,
napi_async_work* result);
[in] env
: The environment that the API is invoked under.[in] execute
: The native function which should be called to excute the logic asynchronously.[in] complete
: The native function which will be called when the asynchronous logic is comple or is cancelled.[in] data
: User-provided data context. This will be passed back into the execute and complete functions.[out] result
:napi_async_work*
which is the handle to the newly created async work.
Returns napi_ok
if the API succeeded.
This API allocates a work object that is used to execute logic asynchronously.
It should be freed using napi_delete_async_work
once the work is no longer
required.
napi_delete_async_work#
NAPI_EXTERN napi_status napi_delete_async_work(napi_env env,
napi_async_work work);
[in] env
: The environment that the API is invoked under.[in] work
: The handle returned by the call tonapi_create_async_work
.
Returns napi_ok
if the API succeeded.
This API frees a previously allocated work object.
napi_queue_async_work#
NAPI_EXTERN napi_status napi_queue_async_work(napi_env env,
napi_async_work work);
[in] env
: The environment that the API is invoked under.[in] work
: The handle returned by the call tonapi_create_async_work
.
Returns napi_ok
if the API succeeded.
This API requests that the previously allocated work be scheduled for execution.
napi_cancel_async_work#
NAPI_EXTERN napi_status napi_cancel_async_work(napi_env env,
napi_async_work work);
[in] env
: The environment that the API is invoked under.[in] work
: The handle returned by the call tonapi_create_async_work
.
Returns napi_ok
if the API succeeded.
This API cancels queued work if it has not yet
been started. If it has already started executing, it cannot be
cancelled and napi_generic_failure
will be returned. If successful,
the complete
callback will be invoked with a status value of
napi_cancelled
. The work should not be deleted before the complete
callback invocation, even if it has been successfully cancelled.
Version Management#
napi_get_version#
NAPI_EXTERN napi_status napi_get_version(napi_env env,
uint32_t* result);
[in] env
: The environment that the API is invoked under.[out] result
: The highest version of N-API supported.
Returns napi_ok
if the API succeeded.
This API returns the highest N-API version supported by the Node.js runtime. N-API is planned to be additive such that newer releases of Node.js may support additional API functions. In order to allow an addon to use a newer function when running with versions of Node.js that support it, while providing fallback behavior when running with Node.js versions that don't support it:
- Call
napi_get_version()
to determine if the API is available. - If available, dynamically load a pointer to the function using
uv_dlsym()
. - Use the dynamically loaded pointer to invoke the function.
- If the function is not available, provide an alternate implementation that does not use the function.
Child Process#
Stability: 2 - Stable
The child_process
module provides the ability to spawn child processes in
a manner that is similar, but not identical, to popen(3). This capability
is primarily provided by the child_process.spawn()
function:
const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
By default, pipes for stdin
, stdout
and stderr
are established between
the parent Node.js process and the spawned child. It is possible to stream data
through these pipes in a non-blocking way. Note, however, that some programs
use line-buffered I/O internally. While that does not affect Node.js, it can
mean that data sent to the child process may not be immediately consumed.
The child_process.spawn()
method spawns the child process asynchronously,
without blocking the Node.js event loop. The child_process.spawnSync()
function provides equivalent functionality in a synchronous manner that blocks
the event loop until the spawned process either exits or is terminated.
For convenience, the child_process
module provides a handful of synchronous
and asynchronous alternatives to child_process.spawn()
and
child_process.spawnSync()
. Note that each of these alternatives are
implemented on top of child_process.spawn()
or child_process.spawnSync()
.
child_process.exec()
: spawns a shell and runs a command within that shell, passing thestdout
andstderr
to a callback function when complete.child_process.execFile()
: similar tochild_process.exec()
except that it spawns the command directly without first spawning a shell.child_process.fork()
: spawns a new Node.js process and invokes a specified module with an IPC communication channel established that allows sending messages between parent and child.child_process.execSync()
: a synchronous version ofchild_process.exec()
that will block the Node.js event loop.child_process.execFileSync()
: a synchronous version ofchild_process.execFile()
that will block the Node.js event loop.
For certain use cases, such as automating shell scripts, the synchronous counterparts may be more convenient. In many cases, however, the synchronous methods can have significant impact on performance due to stalling the event loop while spawned processes complete.
Asynchronous Process Creation#
The child_process.spawn()
, child_process.fork()
, child_process.exec()
,
and child_process.execFile()
methods all follow the idiomatic asynchronous
programming pattern typical of other Node.js APIs.
Each of the methods returns a ChildProcess
instance. These objects
implement the Node.js EventEmitter
API, allowing the parent process to
register listener functions that are called when certain events occur during
the life cycle of the child process.
The child_process.exec()
and child_process.execFile()
methods additionally
allow for an optional callback
function to be specified that is invoked
when the child process terminates.
Spawning .bat
and .cmd
files on Windows#
The importance of the distinction between child_process.exec()
and
child_process.execFile()
can vary based on platform. On Unix-type operating
systems (Unix, Linux, macOS) child_process.execFile()
can be more efficient
because it does not spawn a shell. On Windows, however, .bat
and .cmd
files are not executable on their own without a terminal, and therefore cannot
be launched using child_process.execFile()
. When running on Windows, .bat
and .cmd
files can be invoked using child_process.spawn()
with the shell
option set, with child_process.exec()
, or by spawning cmd.exe
and passing
the .bat
or .cmd
file as an argument (which is what the shell
option and
child_process.exec()
do). In any case, if the script filename contains
spaces it needs to be quoted.
// On Windows Only ...
const { spawn } = require('child_process');
const bat = spawn('cmd.exe', ['/c', 'my.bat']);
bat.stdout.on('data', (data) => {
console.log(data.toString());
});
bat.stderr.on('data', (data) => {
console.log(data.toString());
});
bat.on('exit', (code) => {
console.log(`Child exited with code ${code}`);
});
// OR...
const { exec } = require('child_process');
exec('my.bat', (err, stdout, stderr) => {
if (err) {
console.error(err);
return;
}
console.log(stdout);
});
// Script with spaces in the filename:
const bat = spawn('"my script.cmd"', ['a', 'b'], { shell: true });
// or:
exec('"my script.cmd" a b', (err, stdout, stderr) => {
// ...
});
child_process.exec(command[, options][, callback])#
command
<string> The command to run, with space-separated argumentsoptions
<Object>cwd
<string> Current working directory of the child processenv
<Object> Environment key-value pairsencoding
<string> (Default:'utf8'
)shell
<string> Shell to execute the command with (Default:'/bin/sh'
on UNIX,'cmd.exe'
on Windows, The shell should understand the-c
switch on UNIX or/d /s /c
on Windows. On Windows, command line parsing should be compatible withcmd.exe
.)timeout
<number> (Default:0
)maxBuffer
<number> Largest amount of data in bytes allowed on stdout or stderr. (Default:200*1024
) If exceeded, the child process is terminated. See caveat atmaxBuffer
and Unicode.killSignal
<string> | <integer> (Default:'SIGTERM'
)uid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)
callback
<Function> called with the output when process terminates- Returns: <ChildProcess>
Spawns a shell then executes the command
within that shell, buffering any
generated output. The command
string passed to the exec function is processed
directly by the shell and special characters (vary based on
shell)
need to be dealt with accordingly:
exec('"/path/to/test file/test.sh" arg1 arg2');
//Double quotes are used so that the space in the path is not interpreted as
//multiple arguments
exec('echo "The \\$HOME variable is $HOME"');
//The $HOME variable is escaped in the first instance, but not in the second
Note: Never pass unsanitised user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.
const { exec } = require('child_process');
exec('cat *.js bad_file | wc -l', (error, stdout, stderr) => {
if (error) {
console.error(`exec error: ${error}`);
return;
}
console.log(`stdout: ${stdout}`);
console.log(`stderr: ${stderr}`);
});
If a callback
function is provided, it is called with the arguments
(error, stdout, stderr)
. On success, error
will be null
. On error,
error
will be an instance of Error
. The error.code
property will be
the exit code of the child process while error.signal
will be set to the
signal that terminated the process. Any exit code other than 0
is considered
to be an error.
The stdout
and stderr
arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The encoding
option
can be used to specify the character encoding used to decode the stdout and
stderr output. If encoding
is 'buffer'
, or an unrecognized character
encoding, Buffer
objects will be passed to the callback instead.
The options
argument may be passed as the second argument to customize how
the process is spawned. The default options are:
const defaults = {
encoding: 'utf8',
timeout: 0,
maxBuffer: 200 * 1024,
killSignal: 'SIGTERM',
cwd: null,
env: null
};
If timeout
is greater than 0
, the parent will send the signal
identified by the killSignal
property (the default is 'SIGTERM'
) if the
child runs longer than timeout
milliseconds.
Note: Unlike the exec(3) POSIX system call, child_process.exec()
does not
replace the existing process and uses a shell to execute the command.
If this method is invoked as its util.promisify()
ed version, it returns
a Promise for an object with stdout
and stderr
properties. In case of an
error, a rejected promise is returned, with the same error
object given in the
callback, but with an additional two properties stdout
and stderr
.
For example:
const util = require('util');
const exec = util.promisify(require('child_process').exec);
async function lsExample() {
const { stdout, stderr } = await exec('ls');
console.log('stdout:', stdout);
console.log('stderr:', stderr);
}
lsExample();
child_process.execFile(file[, args][, options][, callback])#
file
<string> The name or path of the executable file to runargs
<Array> List of string argumentsoptions
<Object>cwd
<string> Current working directory of the child processenv
<Object> Environment key-value pairsencoding
<string> (Default:'utf8'
)timeout
<number> (Default:0
)maxBuffer
<number> Largest amount of data in bytes allowed on stdout or stderr. (Default:200*1024
) If exceeded, the child process is terminated. See caveat atmaxBuffer
and Unicode.killSignal
<string> | <integer> (Default:'SIGTERM'
)uid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)
callback
<Function> called with the output when process terminates- Returns: <ChildProcess>
The child_process.execFile()
function is similar to child_process.exec()
except that it does not spawn a shell. Rather, the specified executable file
is spawned directly as a new process making it slightly more efficient than
child_process.exec()
.
The same options as child_process.exec()
are supported. Since a shell is not
spawned, behaviors such as I/O redirection and file globbing are not supported.
const { execFile } = require('child_process');
const child = execFile('node', ['--version'], (error, stdout, stderr) => {
if (error) {
throw error;
}
console.log(stdout);
});
The stdout
and stderr
arguments passed to the callback will contain the
stdout and stderr output of the child process. By default, Node.js will decode
the output as UTF-8 and pass strings to the callback. The encoding
option
can be used to specify the character encoding used to decode the stdout and
stderr output. If encoding
is 'buffer'
, or an unrecognized character
encoding, Buffer
objects will be passed to the callback instead.
If this method is invoked as its util.promisify()
ed version, it returns
a Promise for an object with stdout
and stderr
properties. In case of an
error, a rejected promise is returned, with the same error
object given in the
callback, but with an additional two properties stdout
and stderr
.
const util = require('util');
const execFile = util.promisify(require('child_process').execFile);
async function getVersion() {
const { stdout } = await execFile('node', ['--version']);
console.log(stdout);
}
getVersion();
child_process.fork(modulePath[, args][, options])#
modulePath
<string> The module to run in the childargs
<Array> List of string argumentsoptions
<Object>cwd
<string> Current working directory of the child processenv
<Object> Environment key-value pairsexecPath
<string> Executable used to create the child processexecArgv
<Array> List of string arguments passed to the executable (Default:process.execArgv
)silent
<boolean> Iftrue
, stdin, stdout, and stderr of the child will be piped to the parent, otherwise they will be inherited from the parent, see the'pipe'
and'inherit'
options forchild_process.spawn()
'sstdio
for more details (Default:false
)stdio
<Array> | <string> Seechild_process.spawn()
'sstdio
. When this option is provided, it overridessilent
. If the array variant is used, it must contain exactly one item with value'ipc'
or an error will be thrown. For instance[0, 1, 2, 'ipc']
.uid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)
- Returns: <ChildProcess>
The child_process.fork()
method is a special case of
child_process.spawn()
used specifically to spawn new Node.js processes.
Like child_process.spawn()
, a ChildProcess
object is returned. The returned
ChildProcess
will have an additional communication channel built-in that
allows messages to be passed back and forth between the parent and child. See
child.send()
for details.
It is important to keep in mind that spawned Node.js child processes are independent of the parent with exception of the IPC communication channel that is established between the two. Each process has its own memory, with their own V8 instances. Because of the additional resource allocations required, spawning a large number of child Node.js processes is not recommended.
By default, child_process.fork()
will spawn new Node.js instances using the
process.execPath
of the parent process. The execPath
property in the
options
object allows for an alternative execution path to be used.
Node.js processes launched with a custom execPath
will communicate with the
parent process using the file descriptor (fd) identified using the
environment variable NODE_CHANNEL_FD
on the child process. The input and
output on this fd is expected to be line delimited JSON objects.
Note: Unlike the fork(2) POSIX system call, child_process.fork()
does
not clone the current process.
child_process.spawn(command[, args][, options])#
command
<string> The command to runargs
<Array> List of string argumentsoptions
<Object>cwd
<string> Current working directory of the child processenv
<Object> Environment key-value pairsargv0
<string> Explicitly set the value ofargv[0]
sent to the child process. This will be set tocommand
if not specified.stdio
<Array> | <string> Child's stdio configuration. (Seeoptions.stdio
)detached
<boolean> Prepare child to run independently of its parent process. Specific behavior depends on the platform, seeoptions.detached
)uid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)shell
<boolean> | <string> Iftrue
, runscommand
inside of a shell. Uses'/bin/sh'
on UNIX, and'cmd.exe'
on Windows. A different shell can be specified as a string. The shell should understand the-c
switch on UNIX, or/d /s /c
on Windows. Defaults tofalse
(no shell).
- Returns: <ChildProcess>
The child_process.spawn()
method spawns a new process using the given
command
, with command line arguments in args
. If omitted, args
defaults
to an empty array.
Note: If the shell
option is enabled, do not pass unsanitised user input to
this function. Any input containing shell metacharacters may be used to
trigger arbitrary command execution.
A third argument may be used to specify additional options, with these defaults:
const defaults = {
cwd: undefined,
env: process.env
};
Use cwd
to specify the working directory from which the process is spawned.
If not given, the default is to inherit the current working directory.
Use env
to specify environment variables that will be visible to the new
process, the default is process.env
.
Example of running ls -lh /usr
, capturing stdout
, stderr
, and the
exit code:
const { spawn } = require('child_process');
const ls = spawn('ls', ['-lh', '/usr']);
ls.stdout.on('data', (data) => {
console.log(`stdout: ${data}`);
});
ls.stderr.on('data', (data) => {
console.log(`stderr: ${data}`);
});
ls.on('close', (code) => {
console.log(`child process exited with code ${code}`);
});
Example: A very elaborate way to run ps ax | grep ssh
const { spawn } = require('child_process');
const ps = spawn('ps', ['ax']);
const grep = spawn('grep', ['ssh']);
ps.stdout.on('data', (data) => {
grep.stdin.write(data);
});
ps.stderr.on('data', (data) => {
console.log(`ps stderr: ${data}`);
});
ps.on('close', (code) => {
if (code !== 0) {
console.log(`ps process exited with code ${code}`);
}
grep.stdin.end();
});
grep.stdout.on('data', (data) => {
console.log(data.toString());
});
grep.stderr.on('data', (data) => {
console.log(`grep stderr: ${data}`);
});
grep.on('close', (code) => {
if (code !== 0) {
console.log(`grep process exited with code ${code}`);
}
});
Example of checking for failed spawn
:
const { spawn } = require('child_process');
const child = spawn('bad_command');
child.on('error', (err) => {
console.log('Failed to start child process.');
});
Note: Certain platforms (macOS, Linux) will use the value of argv[0]
for
the process title while others (Windows, SunOS) will use command
.
Note: Node.js currently overwrites argv[0]
with process.execPath
on
startup, so process.argv[0]
in a Node.js child process will not match the
argv0
parameter passed to spawn
from the parent, retrieve it with the
process.argv0
property instead.
options.detached#
On Windows, setting options.detached
to true
makes it possible for the
child process to continue running after the parent exits. The child will have
its own console window. Once enabled for a child process, it cannot be
disabled.
On non-Windows platforms, if options.detached
is set to true
, the child
process will be made the leader of a new process group and session. Note that
child processes may continue running after the parent exits regardless of
whether they are detached or not. See setsid(2) for more information.
By default, the parent will wait for the detached child to exit. To prevent
the parent from waiting for a given child
, use the child.unref()
method.
Doing so will cause the parent's event loop to not include the child in its
reference count, allowing the parent to exit independently of the child, unless
there is an established IPC channel between the child and parent.
When using the detached
option to start a long-running process, the process
will not stay running in the background after the parent exits unless it is
provided with a stdio
configuration that is not connected to the parent.
If the parent's stdio
is inherited, the child will remain attached to the
controlling terminal.
Example of a long-running process, by detaching and also ignoring its parent
stdio
file descriptors, in order to ignore the parent's termination:
const { spawn } = require('child_process');
const child = spawn(process.argv[0], ['child_program.js'], {
detached: true,
stdio: 'ignore'
});
child.unref();
Alternatively one can redirect the child process' output into files:
const fs = require('fs');
const { spawn } = require('child_process');
const out = fs.openSync('./out.log', 'a');
const err = fs.openSync('./out.log', 'a');
const child = spawn('prg', [], {
detached: true,
stdio: [ 'ignore', out, err ]
});
child.unref();
options.stdio#
The options.stdio
option is used to configure the pipes that are established
between the parent and child process. By default, the child's stdin, stdout,
and stderr are redirected to corresponding child.stdin
, child.stdout
, and
child.stderr
streams on the ChildProcess
object. This is equivalent to
setting the options.stdio
equal to ['pipe', 'pipe', 'pipe']
.
For convenience, options.stdio
may be one of the following strings:
'pipe'
- equivalent to['pipe', 'pipe', 'pipe']
(the default)'ignore'
- equivalent to['ignore', 'ignore', 'ignore']
'inherit'
- equivalent to[process.stdin, process.stdout, process.stderr]
or[0,1,2]
Otherwise, the value of options.stdio
is an array where each index corresponds
to an fd in the child. The fds 0, 1, and 2 correspond to stdin, stdout,
and stderr, respectively. Additional fds can be specified to create additional
pipes between the parent and child. The value is one of the following:
'pipe'
- Create a pipe between the child process and the parent process. The parent end of the pipe is exposed to the parent as a property on thechild_process
object aschild.stdio[fd]
. Pipes created for fds 0 - 2 are also available aschild.stdin
,child.stdout
andchild.stderr
, respectively.'ipc'
- Create an IPC channel for passing messages/file descriptors between parent and child. AChildProcess
may have at most one IPC stdio file descriptor. Setting this option enables thechild.send()
method. If the child writes JSON messages to this file descriptor, thechild.on('message')
event handler will be triggered in the parent. If the child is a Node.js process, the presence of an IPC channel will enableprocess.send()
,process.disconnect()
,process.on('disconnect')
, andprocess.on('message')
within the child.'ignore'
- Instructs Node.js to ignore the fd in the child. While Node.js will always open fds 0 - 2 for the processes it spawns, setting the fd to'ignore'
will cause Node.js to open/dev/null
and attach it to the child's fd.- <Stream> object - Share a readable or writable stream that refers to a tty,
file, socket, or a pipe with the child process. The stream's underlying
file descriptor is duplicated in the child process to the fd that
corresponds to the index in the
stdio
array. Note that the stream must have an underlying descriptor (file streams do not until the'open'
event has occurred). - Positive integer - The integer value is interpreted as a file descriptor that is is currently open in the parent process. It is shared with the child process, similar to how <Stream> objects can be shared.
null
,undefined
- Use default value. For stdio fds 0, 1 and 2 (in other words, stdin, stdout, and stderr) a pipe is created. For fd 3 and up, the default is'ignore'
.
Example:
const { spawn } = require('child_process');
// Child will use parent's stdios
spawn('prg', [], { stdio: 'inherit' });
// Spawn child sharing only stderr
spawn('prg', [], { stdio: ['pipe', 'pipe', process.stderr] });
// Open an extra fd=4, to interact with programs presenting a
// startd-style interface.
spawn('prg', [], { stdio: ['pipe', null, null, null, 'pipe'] });
It is worth noting that when an IPC channel is established between the
parent and child processes, and the child is a Node.js process, the child
is launched with the IPC channel unreferenced (using unref()
) until the
child registers an event handler for the process.on('disconnect')
event
or the process.on('message')
event.This allows the child to exit normally
without the process being held open by the open IPC channel.
See also: child_process.exec()
and child_process.fork()
Synchronous Process Creation#
The child_process.spawnSync()
, child_process.execSync()
, and
child_process.execFileSync()
methods are synchronous and WILL block
the Node.js event loop, pausing execution of any additional code until the
spawned process exits.
Blocking calls like these are mostly useful for simplifying general purpose scripting tasks and for simplifying the loading/processing of application configuration at startup.
child_process.execFileSync(file[, args][, options])#
file
<string> The name or path of the executable file to runargs
<Array> List of string argumentsoptions
<Object>cwd
<string> Current working directory of the child processinput
<string> | <Buffer> | <Uint8Array> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<string> | <Array> Child's stdio configuration. (Default:'pipe'
)stderr
by default will be output to the parent process' stderr unlessstdio
is specified
env
<Object> Environment key-value pairsuid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)timeout
<number> In milliseconds the maximum amount of time the process is allowed to run. (Default:undefined
)killSignal
<string> | <integer> The signal value to be used when the spawned process will be killed. (Default:'SIGTERM'
)maxBuffer
<number> Largest amount of data in bytes allowed on stdout or stderr. (Default:200*1024
) If exceeded, the child process is terminated. See caveat atmaxBuffer
and Unicode.encoding
<string> The encoding used for all stdio inputs and outputs. (Default:'buffer'
)
- Returns: <Buffer> | <string> The stdout from the command
The child_process.execFileSync()
method is generally identical to
child_process.execFile()
with the exception that the method will not return
until the child process has fully closed. When a timeout has been encountered
and killSignal
is sent, the method won't return until the process has
completely exited.
Note: If the child process intercepts and handles the SIGTERM
signal and
does not exit, the parent process will still wait until the child process has
exited.
If the process times out, or has a non-zero exit code, this method will
throw. The Error
object will contain the entire result from
child_process.spawnSync()
child_process.execSync(command[, options])#
command
<string> The command to runoptions
<Object>cwd
<string> Current working directory of the child processinput
<string> | <Buffer> | <Uint8Array> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<string> | <Array> Child's stdio configuration. (Default:'pipe'
)stderr
by default will be output to the parent process' stderr unlessstdio
is specified
env
<Object> Environment key-value pairsshell
<string> Shell to execute the command with (Default:'/bin/sh'
on UNIX,'cmd.exe'
on Windows, The shell should understand the-c
switch on UNIX or/d /s /c
on Windows. On Windows, command line parsing should be compatible withcmd.exe
.)uid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)timeout
<number> In milliseconds the maximum amount of time the process is allowed to run. (Default:undefined
)killSignal
<string> | <integer> The signal value to be used when the spawned process will be killed. (Default:'SIGTERM'
)maxBuffer
<number> Largest amount of data in bytes allowed on stdout or stderr. (Default:200*1024
) If exceeded, the child process is terminated. See caveat atmaxBuffer
and Unicode.encoding
<string> The encoding used for all stdio inputs and outputs. (Default:'buffer'
)
- Returns: <Buffer> | <string> The stdout from the command
The child_process.execSync()
method is generally identical to
child_process.exec()
with the exception that the method will not return until
the child process has fully closed. When a timeout has been encountered and
killSignal
is sent, the method won't return until the process has completely
exited. Note that if the child process intercepts and handles the SIGTERM
signal and doesn't exit, the parent process will wait until the child
process has exited.
If the process times out, or has a non-zero exit code, this method will
throw. The Error
object will contain the entire result from
child_process.spawnSync()
Note: Never pass unsanitised user input to this function. Any input containing shell metacharacters may be used to trigger arbitrary command execution.
child_process.spawnSync(command[, args][, options])#
command
<string> The command to runargs
<Array> List of string argumentsoptions
<Object>cwd
<string> Current working directory of the child processinput
<string> | <Buffer> | <Uint8Array> The value which will be passed as stdin to the spawned process- supplying this value will override
stdio[0]
- supplying this value will override
stdio
<string> | <Array> Child's stdio configuration.env
<Object> Environment key-value pairsuid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)timeout
<number> In milliseconds the maximum amount of time the process is allowed to run. (Default:undefined
)killSignal
<string> | <integer> The signal value to be used when the spawned process will be killed. (Default:'SIGTERM'
)maxBuffer
<number> Largest amount of data in bytes allowed on stdout or stderr. (Default:200*1024
) If exceeded, the child process is terminated. See caveat atmaxBuffer
and Unicode.encoding
<string> The encoding used for all stdio inputs and outputs. (Default:'buffer'
)shell
<boolean> | <string> Iftrue
, runscommand
inside of a shell. Uses'/bin/sh'
on UNIX, and'cmd.exe'
on Windows. A different shell can be specified as a string. The shell should understand the-c
switch on UNIX, or/d /s /c
on Windows. Defaults tofalse
(no shell).
- Returns: <Object>
pid
<number> Pid of the child processoutput
<Array> Array of results from stdio outputstdout
<Buffer> | <string> The contents ofoutput[1]
stderr
<Buffer> | <string> The contents ofoutput[2]
status
<number> The exit code of the child processsignal
<string> The signal used to kill the child processerror
<Error> The error object if the child process failed or timed out
The child_process.spawnSync()
method is generally identical to
child_process.spawn()
with the exception that the function will not return
until the child process has fully closed. When a timeout has been encountered
and killSignal
is sent, the method won't return until the process has
completely exited. Note that if the process intercepts and handles the
SIGTERM
signal and doesn't exit, the parent process will wait until the child
process has exited.
Note: If the shell
option is enabled, do not pass unsanitised user input
to this function. Any input containing shell metacharacters may be used to
trigger arbitrary command execution.
Class: ChildProcess#
Instances of the ChildProcess
class are EventEmitters
that represent
spawned child processes.
Instances of ChildProcess
are not intended to be created directly. Rather,
use the child_process.spawn()
, child_process.exec()
,
child_process.execFile()
, or child_process.fork()
methods to create
instances of ChildProcess
.
Event: 'close'#
code
<number> the exit code if the child exited on its own.signal
<string> the signal by which the child process was terminated.
The 'close'
event is emitted when the stdio streams of a child process have
been closed. This is distinct from the 'exit'
event, since multiple
processes might share the same stdio streams.
Event: 'disconnect'#
The 'disconnect'
event is emitted after calling the
child.disconnect()
method in parent process or process.disconnect()
in child process. After
disconnecting it is no longer possible to send or receive messages, and the
child.connected
property is false
.
Event: 'error'#
err
<Error> the error.
The 'error'
event is emitted whenever:
- The process could not be spawned, or
- The process could not be killed, or
- Sending a message to the child process failed.
Note: The 'exit'
event may or may not fire after an error has occurred.
When listening to both the 'exit'
and 'error'
events, it is important
to guard against accidentally invoking handler functions multiple times.
See also child.kill()
and child.send()
.
Event: 'exit'#
code
<number> the exit code if the child exited on its own.signal
<string> the signal by which the child process was terminated.
The 'exit'
event is emitted after the child process ends. If the process
exited, code
is the final exit code of the process, otherwise null
. If the
process terminated due to receipt of a signal, signal
is the string name of
the signal, otherwise null
. One of the two will always be non-null.
Note that when the 'exit'
event is triggered, child process stdio streams
might still be open.
Also, note that Node.js establishes signal handlers for SIGINT
and
SIGTERM
and Node.js processes will not terminate immediately due to receipt
of those signals. Rather, Node.js will perform a sequence of cleanup actions
and then will re-raise the handled signal.
See waitpid(2).
Event: 'message'#
message
<Object> a parsed JSON object or primitive value.sendHandle
<Handle> anet.Socket
ornet.Server
object, or undefined.
The 'message'
event is triggered when a child process uses process.send()
to send messages.
child.channel#
- <Object> A pipe representing the IPC channel to the child process.
The child.channel
property is a reference to the child's IPC channel. If no
IPC channel currently exists, this property is undefined
.
child.connected#
- <boolean> Set to
false
afterchild.disconnect()
is called
The child.connected
property indicates whether it is still possible to send
and receive messages from a child process. When child.connected
is false
, it
is no longer possible to send or receive messages.
child.disconnect()#
Closes the IPC channel between parent and child, allowing the child to exit
gracefully once there are no other connections keeping it alive. After calling
this method the child.connected
and process.connected
properties in both
the parent and child (respectively) will be set to false
, and it will be no
longer possible to pass messages between the processes.
The 'disconnect'
event will be emitted when there are no messages in the
process of being received. This will most often be triggered immediately after
calling child.disconnect()
.
Note that when the child process is a Node.js instance (e.g. spawned using
child_process.fork()
), the process.disconnect()
method can be invoked
within the child process to close the IPC channel as well.
child.kill([signal])#
signal
<string>
The child.kill()
methods sends a signal to the child process. If no argument
is given, the process will be sent the 'SIGTERM'
signal. See signal(7) for
a list of available signals.
const { spawn } = require('child_process');
const grep = spawn('grep', ['ssh']);
grep.on('close', (code, signal) => {
console.log(
`child process terminated due to receipt of signal ${signal}`);
});
// Send SIGHUP to process
grep.kill('SIGHUP');
The ChildProcess
object may emit an 'error'
event if the signal cannot be
delivered. Sending a signal to a child process that has already exited is not
an error but may have unforeseen consequences. Specifically, if the process
identifier (PID) has been reassigned to another process, the signal will be
delivered to that process instead which can have unexpected results.
Note that while the function is called kill
, the signal delivered to the
child process may not actually terminate the process.
See kill(2) for reference.
Also note: on Linux, child processes of child processes will not be terminated
when attempting to kill their parent. This is likely to happen when running a
new process in a shell or with use of the shell
option of ChildProcess
, such
as in this example:
'use strict';
const { spawn } = require('child_process');
const child = spawn(
'sh',
[
'-c',
`node -e "setInterval(() => {
console.log(process.pid, 'is alive')
}, 500);"`
], {
stdio: ['inherit', 'inherit', 'inherit']
}
);
setTimeout(() => {
child.kill(); // does not terminate the node process in the shell
}, 2000);
child.pid#
- <number> Integer
Returns the process identifier (PID) of the child process.
Example:
const { spawn } = require('child_process');
const grep = spawn('grep', ['ssh']);
console.log(`Spawned child pid: ${grep.pid}`);
grep.stdin.end();
child.send(message[, sendHandle[, options]][, callback])#
message
<Object>sendHandle
<Handle>options
<Object>callback
<Function>- Returns: <boolean>
When an IPC channel has been established between the parent and child (
i.e. when using child_process.fork()
), the child.send()
method can be
used to send messages to the child process. When the child process is a Node.js
instance, these messages can be received via the process.on('message')
event.
For example, in the parent script:
const cp = require('child_process');
const n = cp.fork(`${__dirname}/sub.js`);
n.on('message', (m) => {
console.log('PARENT got message:', m);
});
n.send({ hello: 'world' });
And then the child script, 'sub.js'
might look like this:
process.on('message', (m) => {
console.log('CHILD got message:', m);
});
process.send({ foo: 'bar' });
Child Node.js processes will have a process.send()
method of their own that
allows the child to send messages back to the parent.
There is a special case when sending a {cmd: 'NODE_foo'}
message. All messages
containing a NODE_
prefix in its cmd
property are considered to be reserved
for use within Node.js core and will not be emitted in the child's
process.on('message')
event. Rather, such messages are emitted using the
process.on('internalMessage')
event and are consumed internally by Node.js.
Applications should avoid using such messages or listening for
'internalMessage'
events as it is subject to change without notice.
The optional sendHandle
argument that may be passed to child.send()
is for
passing a TCP server or socket object to the child process. The child will
receive the object as the second argument passed to the callback function
registered on the process.on('message')
event. Any data that is received
and buffered in the socket will not be sent to the child.
The options
argument, if present, is an object used to parameterize the
sending of certain types of handles. options
supports the following
properties:
keepOpen
- A Boolean value that can be used when passing instances ofnet.Socket
. Whentrue
, the socket is kept open in the sending process. Defaults tofalse
.
The optional callback
is a function that is invoked after the message is
sent but before the child may have received it. The function is called with a
single argument: null
on success, or an Error
object on failure.
If no callback
function is provided and the message cannot be sent, an
'error'
event will be emitted by the ChildProcess
object. This can happen,
for instance, when the child process has already exited.
child.send()
will return false
if the channel has closed or when the
backlog of unsent messages exceeds a threshold that makes it unwise to send
more. Otherwise, the method returns true
. The callback
function can be
used to implement flow control.
Example: sending a server object#
The sendHandle
argument can be used, for instance, to pass the handle of
a TCP server object to the child process as illustrated in the example below:
const child = require('child_process').fork('child.js');
// Open up the server object and send the handle.
const server = require('net').createServer();
server.on('connection', (socket) => {
socket.end('handled by parent');
});
server.listen(1337, () => {
child.send('server', server);
});
The child would then receive the server object as:
process.on('message', (m, server) => {
if (m === 'server') {
server.on('connection', (socket) => {
socket.end('handled by child');
});
}
});
Once the server is now shared between the parent and child, some connections can be handled by the parent and some by the child.
While the example above uses a server created using the net
module, dgram
module servers use exactly the same workflow with the exceptions of listening on
a 'message'
event instead of 'connection'
and using server.bind()
instead of
server.listen()
. This is, however, currently only supported on UNIX platforms.
Example: sending a socket object#
Similarly, the sendHandler
argument can be used to pass the handle of a
socket to the child process. The example below spawns two children that each
handle connections with "normal" or "special" priority:
const normal = require('child_process').fork('child.js', ['normal']);
const special = require('child_process').fork('child.js', ['special']);
// Open up the server and send sockets to child. Use pauseOnConnect to prevent
// the sockets from being read before they are sent to the child process.
const server = require('net').createServer({ pauseOnConnect: true });
server.on('connection', (socket) => {
// If this is special priority
if (socket.remoteAddress === '74.125.127.100') {
special.send('socket', socket);
return;
}
// This is normal priority
normal.send('socket', socket);
});
server.listen(1337);
The child.js
would receive the socket handle as the second argument passed
to the event callback function:
process.on('message', (m, socket) => {
if (m === 'socket') {
if (socket) {
// Check that the client socket exists.
// It is possible for the socket to be closed between the time it is
// sent and the time it is received in the child process.
socket.end(`Request handled with ${process.argv[2]} priority`);
}
}
});
Once a socket has been passed to a child, the parent is no longer capable of
tracking when the socket is destroyed. To indicate this, the .connections
property becomes null
. It is recommended not to use .maxConnections
when
this occurs.
It is also recommended that any 'message'
handlers in the child process
verify that socket
exists, as the connection may have been closed during the
time it takes to send the connection to the child.
Note: This function uses JSON.stringify()
internally to serialize the
message
.
child.stderr#
A Readable Stream
that represents the child process's stderr
.
If the child was spawned with stdio[2]
set to anything other than 'pipe'
,
then this will be null
.
child.stderr
is an alias for child.stdio[2]
. Both properties will refer to
the same value.
child.stdin#
A Writable Stream
that represents the child process's stdin
.
Note that if a child process waits to read all of its input, the child will not
continue until this stream has been closed via end()
.
If the child was spawned with stdio[0]
set to anything other than 'pipe'
,
then this will be null
.
child.stdin
is an alias for child.stdio[0]
. Both properties will refer to
the same value.
child.stdio#
A sparse array of pipes to the child process, corresponding with positions in
the stdio
option passed to child_process.spawn()
that have been set
to the value 'pipe'
. Note that child.stdio[0]
, child.stdio[1]
, and
child.stdio[2]
are also available as child.stdin
, child.stdout
, and
child.stderr
, respectively.
In the following example, only the child's fd 1
(stdout) is configured as a
pipe, so only the parent's child.stdio[1]
is a stream, all other values in
the array are null
.
const assert = require('assert');
const fs = require('fs');
const child_process = require('child_process');
const child = child_process.spawn('ls', {
stdio: [
0, // Use parent's stdin for child
'pipe', // Pipe child's stdout to parent
fs.openSync('err.out', 'w') // Direct child's stderr to a file
]
});
assert.strictEqual(child.stdio[0], null);
assert.strictEqual(child.stdio[0], child.stdin);
assert(child.stdout);
assert.strictEqual(child.stdio[1], child.stdout);
assert.strictEqual(child.stdio[2], null);
assert.strictEqual(child.stdio[2], child.stderr);
child.stdout#
A Readable Stream
that represents the child process's stdout
.
If the child was spawned with stdio[1]
set to anything other than 'pipe'
,
then this will be null
.
child.stdout
is an alias for child.stdio[1]
. Both properties will refer
to the same value.
maxBuffer
and Unicode#
The maxBuffer
option specifies the largest number of bytes allowed on stdout
or stderr
. If this value is exceeded, then the child process is terminated.
This impacts output that includes multibyte character encodings such as UTF-8 or
UTF-16. For instance, console.log('中文测试')
will send 13 UTF-8 encoded bytes
to stdout
although there are only 4 characters.
Cluster#
Stability: 2 - Stable
A single instance of Node.js runs in a single thread. To take advantage of multi-core systems the user will sometimes want to launch a cluster of Node.js processes to handle the load.
The cluster module allows easy creation of child processes that all share server ports.
const cluster = require('cluster');
const http = require('http');
const numCPUs = require('os').cpus().length;
if (cluster.isMaster) {
console.log(`Master ${process.pid} is running`);
// Fork workers.
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
cluster.on('exit', (worker, code, signal) => {
console.log(`worker ${worker.process.pid} died`);
});
} else {
// Workers can share any TCP connection
// In this case it is an HTTP server
http.createServer((req, res) => {
res.writeHead(200);
res.end('hello world\n');
}).listen(8000);
console.log(`Worker ${process.pid} started`);
}
Running Node.js will now share port 8000 between the workers:
$ node server.js
Master 3596 is running
Worker 4324 started
Worker 4520 started
Worker 6056 started
Worker 5644 started
Please note that on Windows, it is not yet possible to set up a named pipe server in a worker.
How It Works#
The worker processes are spawned using the child_process.fork()
method,
so that they can communicate with the parent via IPC and pass server
handles back and forth.
The cluster module supports two methods of distributing incoming connections.
The first one (and the default one on all platforms except Windows), is the round-robin approach, where the master process listens on a port, accepts new connections and distributes them across the workers in a round-robin fashion, with some built-in smarts to avoid overloading a worker process.
The second approach is where the master process creates the listen socket and sends it to interested workers. The workers then accept incoming connections directly.
The second approach should, in theory, give the best performance. In practice however, distribution tends to be very unbalanced due to operating system scheduler vagaries. Loads have been observed where over 70% of all connections ended up in just two processes, out of a total of eight.
Because server.listen()
hands off most of the work to the master
process, there are three cases where the behavior between a normal
Node.js process and a cluster worker differs:
server.listen({fd: 7})
Because the message is passed to the master, file descriptor 7 in the parent will be listened on, and the handle passed to the worker, rather than listening to the worker's idea of what the number 7 file descriptor references.server.listen(handle)
Listening on handles explicitly will cause the worker to use the supplied handle, rather than talk to the master process.server.listen(0)
Normally, this will cause servers to listen on a random port. However, in a cluster, each worker will receive the same "random" port each time they dolisten(0)
. In essence, the port is random the first time, but predictable thereafter. To listen on a unique port, generate a port number based on the cluster worker ID.
Note: Node.js does not provide routing logic. It is, therefore important to design an application such that it does not rely too heavily on in-memory data objects for things like sessions and login.
Because workers are all separate processes, they can be killed or re-spawned depending on a program's needs, without affecting other workers. As long as there are some workers still alive, the server will continue to accept connections. If no workers are alive, existing connections will be dropped and new connections will be refused. Node.js does not automatically manage the number of workers, however. It is the application's responsibility to manage the worker pool based on its own needs.
Class: Worker#
A Worker object contains all public information and method about a worker.
In the master it can be obtained using cluster.workers
. In a worker
it can be obtained using cluster.worker
.
Event: 'disconnect'#
Similar to the cluster.on('disconnect')
event, but specific to this worker.
cluster.fork().on('disconnect', () => {
// Worker has disconnected
});
Event: 'error'#
This event is the same as the one provided by child_process.fork()
.
Within a worker, process.on('error')
may also be used.
Event: 'exit'#
code
<number> the exit code, if it exited normally.signal
<string> the name of the signal (e.g.'SIGHUP'
) that caused the process to be killed.
Similar to the cluster.on('exit')
event, but specific to this worker.
const worker = cluster.fork();
worker.on('exit', (code, signal) => {
if (signal) {
console.log(`worker was killed by signal: ${signal}`);
} else if (code !== 0) {
console.log(`worker exited with error code: ${code}`);
} else {
console.log('worker success!');
}
});
Event: 'listening'#
address
<Object>
Similar to the cluster.on('listening')
event, but specific to this worker.
cluster.fork().on('listening', (address) => {
// Worker is listening
});
It is not emitted in the worker.
Event: 'message'#
message
<Object>handle
<undefined> | <Object>
Similar to the cluster.on('message')
event, but specific to this worker.
Within a worker, process.on('message)
may also be used.
As an example, here is a cluster that keeps count of the number of requests in the master process using the message system:
const cluster = require('cluster');
const http = require('http');
if (cluster.isMaster) {
// Keep track of http requests
let numReqs = 0;
setInterval(() => {
console.log(`numReqs = ${numReqs}`);
}, 1000);
// Count requests
function messageHandler(msg) {
if (msg.cmd && msg.cmd === 'notifyRequest') {
numReqs += 1;
}
}
// Start workers and listen for messages containing notifyRequest
const numCPUs = require('os').cpus().length;
for (let i = 0; i < numCPUs; i++) {
cluster.fork();
}
for (const id in cluster.workers) {
cluster.workers[id].on('message', messageHandler);
}
} else {
// Worker processes have a http server.
http.Server((req, res) => {
res.writeHead(200);
res.end('hello world\n');
// notify master about the request
process.send({ cmd: 'notifyRequest' });
}).listen(8000);
}
Event: 'online'#
Similar to the cluster.on('online')
event, but specific to this worker.
cluster.fork().on('online', () => {
// Worker is online
});
It is not emitted in the worker.
worker.disconnect()#
- Returns: <Worker> A reference to
worker
.
In a worker, this function will close all servers, wait for the 'close'
event on
those servers, and then disconnect the IPC channel.
In the master, an internal message is sent to the worker causing it to call
.disconnect()
on itself.
Causes .exitedAfterDisconnect
to be set.
Note that after a server is closed, it will no longer accept new connections,
but connections may be accepted by any other listening worker. Existing
connections will be allowed to close as usual. When no more connections exist,
see server.close()
, the IPC channel to the worker will close allowing it to
die gracefully.
The above applies only to server connections, client connections are not automatically closed by workers, and disconnect does not wait for them to close before exiting.
Note that in a worker, process.disconnect
exists, but it is not this function,
it is disconnect
.
Because long living server connections may block workers from disconnecting, it
may be useful to send a message, so application specific actions may be taken to
close them. It also may be useful to implement a timeout, killing a worker if
the 'disconnect'
event has not been emitted after some time.
if (cluster.isMaster) {
const worker = cluster.fork();
let timeout;
worker.on('listening', (address) => {
worker.send('shutdown');
worker.disconnect();
timeout = setTimeout(() => {
worker.kill();
}, 2000);
});
worker.on('disconnect', () => {
clearTimeout(timeout);
});
} else if (cluster.isWorker) {
const net = require('net');
const server = net.createServer((socket) => {
// connections never end
});
server.listen(8000);
process.on('message', (msg) => {
if (msg === 'shutdown') {
// initiate graceful close of any connections to server
}
});
}
worker.exitedAfterDisconnect#
Set by calling .kill()
or .disconnect()
. Until then, it is undefined
.
The boolean worker.exitedAfterDisconnect
allows distinguishing between
voluntary and accidental exit, the master may choose not to respawn a worker
based on this value.
cluster.on('exit', (worker, code, signal) => {
if (worker.exitedAfterDisconnect === true) {
console.log('Oh, it was just voluntary – no need to worry');
}
});
// kill worker
worker.kill();
worker.id#
Each new worker is given its own unique id, this id is stored in the
id
.
While a worker is alive, this is the key that indexes it in cluster.workers
worker.isConnected()#
This function returns true
if the worker is connected to its master via its
IPC channel, false
otherwise. A worker is connected to its master after it
has been created. It is disconnected after the 'disconnect'
event is emitted.
worker.isDead()#
This function returns true
if the worker's process has terminated (either
because of exiting or being signaled). Otherwise, it returns false
.
worker.kill([signal='SIGTERM'])#
signal
<string> Name of the kill signal to send to the worker process.
This function will kill the worker. In the master, it does this by disconnecting
the worker.process
, and once disconnected, killing with signal
. In the
worker, it does it by disconnecting the channel, and then exiting with code 0
.
Causes .exitedAfterDisconnect
to be set.
This method is aliased as worker.destroy()
for backwards compatibility.
Note that in a worker, process.kill()
exists, but it is not this function,
it is kill
.
worker.process#
All workers are created using child_process.fork()
, the returned object
from this function is stored as .process
. In a worker, the global process
is stored.
See: Child Process module
Note that workers will call process.exit(0)
if the 'disconnect'
event occurs
on process
and .exitedAfterDisconnect
is not true
. This protects against
accidental disconnection.
worker.send(message[, sendHandle][, callback])#
message
<Object>sendHandle
<Handle>callback
<Function>- Returns: Boolean
Send a message to a worker or master, optionally with a handle.
In the master this sends a message to a specific worker. It is identical to
ChildProcess.send()
.
In a worker this sends a message to the master. It is identical to
process.send()
.
This example will echo back all messages from the master:
if (cluster.isMaster) {
const worker = cluster.fork();
worker.send('hi there');
} else if (cluster.isWorker) {
process.on('message', (msg) => {
process.send(msg);
});
}
worker.suicide#
Stability: 0 - Deprecated: Use worker.exitedAfterDisconnect
instead.
An alias to worker.exitedAfterDisconnect
.
Set by calling .kill()
or .disconnect()
. Until then, it is undefined
.
The boolean worker.suicide
is used to distinguish between voluntary
and accidental exit, the master may choose not to respawn a worker based on
this value.
cluster.on('exit', (worker, code, signal) => {
if (worker.suicide === true) {
console.log('Oh, it was just voluntary – no need to worry');
}
});
// kill worker
worker.kill();
This API only exists for backwards compatibility and will be removed in the future.
Event: 'disconnect'#
worker
<cluster.Worker>
Emitted after the worker IPC channel has disconnected. This can occur when a worker exits gracefully, is killed, or is disconnected manually (such as with worker.disconnect()).
There may be a delay between the 'disconnect'
and 'exit'
events. These events
can be used to detect if the process is stuck in a cleanup or if there are
long-living connections.
cluster.on('disconnect', (worker) => {
console.log(`The worker #${worker.id} has disconnected`);
});
Event: 'exit'#
worker
<cluster.Worker>code
<number> the exit code, if it exited normally.signal
<string> the name of the signal (e.g.'SIGHUP'
) that caused the process to be killed.
When any of the workers die the cluster module will emit the 'exit'
event.
This can be used to restart the worker by calling .fork()
again.
cluster.on('exit', (worker, code, signal) => {
console.log('worker %d died (%s). restarting...',
worker.process.pid, signal || code);
cluster.fork();
});
See child_process event: 'exit'.
Event: 'fork'#
worker
<cluster.Worker>
When a new worker is forked the cluster module will emit a 'fork'
event.
This can be used to log worker activity, and create a custom timeout.
const timeouts = [];
function errorMsg() {
console.error('Something must be wrong with the connection ...');
}
cluster.on('fork', (worker) => {
timeouts[worker.id] = setTimeout(errorMsg, 2000);
});
cluster.on('listening', (worker, address) => {
clearTimeout(timeouts[worker.id]);
});
cluster.on('exit', (worker, code, signal) => {
clearTimeout(timeouts[worker.id]);
errorMsg();
});
Event: 'listening'#
worker
<cluster.Worker>address
<Object>
After calling listen()
from a worker, when the 'listening'
event is emitted
on the server a 'listening'
event will also be emitted on cluster
in the
master.
The event handler is executed with two arguments, the worker
contains the
worker object and the address
object contains the following connection
properties: address
, port
and addressType
. This is very useful if the
worker is listening on more than one address.
cluster.on('listening', (worker, address) => {
console.log(
`A worker is now connected to ${address.address}:${address.port}`);
});
The addressType
is one of:
4
(TCPv4)6
(TCPv6)-1
(unix domain socket)"udp4"
or"udp6"
(UDP v4 or v6)
Event: 'message'#
worker
<cluster.Worker>message
<Object>handle
<undefined> | <Object>
Emitted when the cluster master receives a message from any worker.
See child_process event: 'message'.
Before Node.js v6.0, this event emitted only the message and the handle, but not the worker object, contrary to what the documentation stated.
If support for older versions is required but a worker object is not required, it is possible to work around the discrepancy by checking the number of arguments:
cluster.on('message', (worker, message, handle) => {
if (arguments.length === 2) {
handle = message;
message = worker;
worker = undefined;
}
// ...
});
Event: 'online'#
worker
<cluster.Worker>
After forking a new worker, the worker should respond with an online message.
When the master receives an online message it will emit this event.
The difference between 'fork'
and 'online'
is that fork is emitted when the
master forks a worker, and 'online' is emitted when the worker is running.
cluster.on('online', (worker) => {
console.log('Yay, the worker responded after it was forked');
});
Event: 'setup'#
settings
<Object>
Emitted every time .setupMaster()
is called.
The settings
object is the cluster.settings
object at the time
.setupMaster()
was called and is advisory only, since multiple calls to
.setupMaster()
can be made in a single tick.
If accuracy is important, use cluster.settings
.
cluster.disconnect([callback])#
callback
<Function> called when all workers are disconnected and handles are closed
Calls .disconnect()
on each worker in cluster.workers
.
When they are disconnected all internal handles will be closed, allowing the master process to die gracefully if no other event is waiting.
The method takes an optional callback argument which will be called when finished.
This can only be called from the master process.
cluster.fork([env])#
env
<Object> Key/value pairs to add to worker process environment.- return <cluster.Worker>
Spawn a new worker process.
This can only be called from the master process.
cluster.isMaster#
True if the process is a master. This is determined
by the process.env.NODE_UNIQUE_ID
. If process.env.NODE_UNIQUE_ID
is
undefined, then isMaster
is true
.
cluster.isWorker#
True if the process is not a master (it is the negation of cluster.isMaster
).
cluster.schedulingPolicy#
The scheduling policy, either cluster.SCHED_RR
for round-robin or
cluster.SCHED_NONE
to leave it to the operating system. This is a
global setting and effectively frozen once either the first worker is spawned,
or cluster.setupMaster()
is called, whichever comes first.
SCHED_RR
is the default on all operating systems except Windows.
Windows will change to SCHED_RR
once libuv is able to effectively
distribute IOCP handles without incurring a large performance hit.
cluster.schedulingPolicy
can also be set through the
NODE_CLUSTER_SCHED_POLICY
environment variable. Valid
values are "rr"
and "none"
.
cluster.settings#
- <Object>
execArgv
<Array> List of string arguments passed to the Node.js executable. (Default=process.execArgv
)exec
<string> File path to worker file. (Default=process.argv[1]
)args
<Array> String arguments passed to worker. (Default=process.argv.slice(2)
)silent
<boolean> Whether or not to send output to parent's stdio. (Default=false
)stdio
<Array> Configures the stdio of forked processes. Because the cluster module relies on IPC to function, this configuration must contain an'ipc'
entry. When this option is provided, it overridessilent
.uid
<number> Sets the user identity of the process. (See setuid(2).)gid
<number> Sets the group identity of the process. (See setgid(2).)inspectPort
<number> | <function> Sets inspector port of worker. This can be a number, or a function that takes no arguments and returns a number. By default each worker gets its own port, incremented from the master'sprocess.debugPort
.
After calling .setupMaster()
(or .fork()
) this settings object will contain
the settings, including the default values.
This object is not intended to be changed or set manually.
cluster.setupMaster([settings])#
settings
<Object> seecluster.settings
setupMaster
is used to change the default 'fork' behavior. Once called,
the settings will be present in cluster.settings
.
Note that:
- Any settings changes only affect future calls to
.fork()
and have no effect on workers that are already running. - The only attribute of a worker that cannot be set via
.setupMaster()
is theenv
passed to.fork()
. - The defaults above apply to the first call only, the defaults for later
calls is the current value at the time of
cluster.setupMaster()
is called.
Example:
const cluster = require('cluster');
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'https'],
silent: true
});
cluster.fork(); // https worker
cluster.setupMaster({
exec: 'worker.js',
args: ['--use', 'http']
});
cluster.fork(); // http worker
This can only be called from the master process.
cluster.worker#
A reference to the current worker object. Not available in the master process.
const cluster = require('cluster');
if (cluster.isMaster) {
console.log('I am master');
cluster.fork();
cluster.fork();
} else if (cluster.isWorker) {
console.log(`I am worker #${cluster.worker.id}`);
}
cluster.workers#
A hash that stores the active worker objects, keyed by id
field. Makes it
easy to loop through all the workers. It is only available in the master
process.
A worker is removed from cluster.workers after the worker has disconnected and
exited. The order between these two events cannot be determined in advance.
However, it is guaranteed that the removal from the cluster.workers list happens
before last 'disconnect'
or 'exit'
event is emitted.
// Go through all workers
function eachWorker(callback) {
for (const id in cluster.workers) {
callback(cluster.workers[id]);
}
}
eachWorker((worker) => {
worker.send('big announcement to all workers');
});
Using the worker's unique id is the easiest way to locate the worker.
socket.on('data', (id) => {
const worker = cluster.workers[id];
});
Command Line Options#
Node.js comes with a variety of CLI options. These options expose built-in debugging, multiple ways to execute scripts, and other helpful runtime options.
To view this documentation as a manual page in a terminal, run man node
.
Synopsis#
node [options] [v8 options] [script.js | -e "script" | -] [--] [arguments]
node debug [script.js | -e "script" | <host>:<port>] …
node --v8-options
Execute without arguments to start the REPL.
For more info about node debug
, please see the debugger documentation.
Options#
-v
, --version
#
Print node's version.
-h
, --help
#
Print node command line options. The output of this option is less detailed than this document.
-e
, --eval "script"
#
Evaluate the following argument as JavaScript. The modules which are
predefined in the REPL can also be used in script
.
-p
, --print "script"
#
Identical to -e
but prints the result.
-c
, --check
#
Syntax check the script without executing.
-i
, --interactive
#
Opens the REPL even if stdin does not appear to be a terminal.
-r
, --require module
#
Preload the specified module at startup.
Follows require()
's module resolution
rules. module
may be either a path to a file, or a node module name.
--inspect[=[host:]port]
#
Activate inspector on host:port. Default is 127.0.0.1:9229.
V8 inspector integration allows tools such as Chrome DevTools and IDEs to debug and profile Node.js instances. The tools attach to Node.js instances via a tcp port and communicate using the Chrome Debugging Protocol.
--inspect-brk[=[host:]port]
#
Activate inspector on host:port and break at start of user script. Default host:port is 127.0.0.1:9229.
--inspect-port=[host:]port
#
Set the host:port to be used when the inspector is activated.
Useful when activating the inspector by sending the SIGUSR1
signal.
Default host is 127.0.0.1.
--no-deprecation
#
Silence deprecation warnings.
--trace-deprecation
#
Print stack traces for deprecations.
--throw-deprecation
#
Throw errors for deprecations.
--pending-deprecation
#
Emit pending deprecation warnings.
Note: Pending deprecations are generally identical to a runtime deprecation
with the notable exception that they are turned off by default and will not
be emitted unless either the --pending-deprecation
command line flag, or the
NODE_PENDING_DEPRECATION=1
environment variable, is set. Pending deprecations
are used to provide a kind of selective "early warning" mechanism that
developers may leverage to detect deprecated API usage.
--no-warnings
#
Silence all process warnings (including deprecations).
--napi-modules
#
Enable loading native modules compiled with the ABI-stable Node.js API (N-API) (experimental).
--abort-on-uncaught-exception
#
Aborting instead of exiting causes a core file to be generated for post-mortem
analysis using a debugger (such as lldb
, gdb
, and mdb
).
--trace-warnings
#
Print stack traces for process warnings (including deprecations).
--redirect-warnings=file
#
Write process warnings to the given file instead of printing to stderr. The file will be created if it does not exist, and will be appended to if it does. If an error occurs while attempting to write the warning to the file, the warning will be written to stderr instead.
--trace-sync-io
#
Prints a stack trace whenever synchronous I/O is detected after the first turn of the event loop.
--trace-events-enabled
#
Enables the collection of trace event tracing information.
--trace-event-categories
#
A comma separated list of categories that should be traced when trace event
tracing is enabled using --trace-events-enabled
.
--zero-fill-buffers
#
Automatically zero-fills all newly allocated Buffer and SlowBuffer instances.
--preserve-symlinks
#
Instructs the module loader to preserve symbolic links when resolving and caching modules.
By default, when Node.js loads a module from a path that is symbolically linked
to a different on-disk location, Node.js will dereference the link and use the
actual on-disk "real path" of the module as both an identifier and as a root
path to locate other dependency modules. In most cases, this default behavior
is acceptable. However, when using symbolically linked peer dependencies, as
illustrated in the example below, the default behavior causes an exception to
be thrown if moduleA
attempts to require moduleB
as a peer dependency:
{appDir}
├── app
│ ├── index.js
│ └── node_modules
│ ├── moduleA -> {appDir}/moduleA
│ └── moduleB
│ ├── index.js
│ └── package.json
└── moduleA
├── index.js
└── package.json
The --preserve-symlinks
command line flag instructs Node.js to use the
symlink path for modules as opposed to the real path, allowing symbolically
linked peer dependencies to be found.
Note, however, that using --preserve-symlinks
can have other side effects.
Specifically, symbolically linked native modules can fail to load if those
are linked from more than one location in the dependency tree (Node.js would
see those as two separate modules and would attempt to load the module multiple
times, causing an exception to be thrown).
--track-heap-objects
#
Track heap object allocations for heap snapshots.
--prof-process
#
Process v8 profiler output generated using the v8 option --prof
.
--v8-options
#
Print v8 command line options.
Note: V8 options allow words to be separated by both dashes (-
) or
underscores (_
).
For example, --stack-trace-limit
is equivalent to --stack_trace_limit
.
--tls-cipher-list=list
#
Specify an alternative default TLS cipher list. (Requires Node.js to be built with crypto support. (Default))
--enable-fips
#
Enable FIPS-compliant crypto at startup. (Requires Node.js to be built with
./configure --openssl-fips
)
--force-fips
#
Force FIPS-compliant crypto on startup. (Cannot be disabled from script code.)
(Same requirements as --enable-fips
)
--openssl-config=file
#
Load an OpenSSL configuration file on startup. Among other uses, this can be
used to enable FIPS-compliant crypto if Node.js is built with
./configure --openssl-fips
.
--use-openssl-ca
, --use-bundled-ca
#
Use OpenSSL's default CA store or use bundled Mozilla CA store as supplied by current NodeJS version. The default store is selectable at build-time.
Using OpenSSL store allows for external modifications of the store. For most Linux and BSD distributions, this store is maintained by the distribution maintainers and system administrators. OpenSSL CA store location is dependent on configuration of the OpenSSL library but this can be altered at runtime using environmental variables.
The bundled CA store, as supplied by NodeJS, is a snapshot of Mozilla CA store that is fixed at release time. It is identical on all supported platforms.
See SSL_CERT_DIR
and SSL_CERT_FILE
.
--icu-data-dir=file
#
Specify ICU data load path. (overrides NODE_ICU_DATA
)
-
#
Alias for stdin, analogous to the use of - in other command line utilities, meaning that the script will be read from stdin, and the rest of the options are passed to that script.
--
#
Indicate the end of node options. Pass the rest of the arguments to the script. If no script filename or eval/print script is supplied prior to this, then the next argument will be used as a script filename.
Environment Variables#
NODE_DEBUG=module[,…]
#
','
-separated list of core modules that should print debug information.
NODE_PATH=path[:…]
#
':'
-separated list of directories prefixed to the module search path.
Note: On Windows, this is a ';'
-separated list instead.
NODE_DISABLE_COLORS=1
#
When set to 1
colors will not be used in the REPL.
NODE_ICU_DATA=file
#
Data path for ICU (Intl object) data. Will extend linked-in data when compiled with small-icu support.
NODE_NO_WARNINGS=1
#
When set to 1
, process warnings are silenced.
NODE_OPTIONS=options...
#
options...
are interpreted as if they had been specified on the command line
before the actual command line (so they can be overridden). Node will exit with
an error if an option that is not allowed in the environment is used, such as
-p
or a script file.
Node options that are allowed are:
--enable-fips
--force-fips
--icu-data-dir
--inspect-brk
--inspect-port
--inspect
--napi-modules
--no-deprecation
--no-warnings
--openssl-config
--redirect-warnings
--require
,-r
--throw-deprecation
--tls-cipher-list
--trace-deprecation
--trace-events-categories
--trace-events-enabled
--trace-sync-io
--trace-warnings
--track-heap-objects
--use-bundled-ca
--use-openssl-ca
--v8-pool-size
--zero-fill-buffers
V8 options that are allowed are:
--abort-on-uncaught-exception
--max-old-space-size
NODE_PENDING_DEPRECATION=1
#
When set to 1
, emit pending deprecation warnings.
Note: Pending deprecations are generally identical to a runtime deprecation
with the notable exception that they are turned off by default and will not
be emitted unless either the --pending-deprecation
command line flag, or the
NODE_PENDING_DEPRECATION=1
environment variable, is set. Pending deprecations
are used to provide a kind of selective "early warning" mechanism that
developers may leverage to detect deprecated API usage.
NODE_PRESERVE_SYMLINKS=1
#
When set to 1
, instructs the module loader to preserve symbolic links when
resolving and caching modules.
NODE_REPL_HISTORY=file
#
Path to the file used to store the persistent REPL history. The default path is
~/.node_repl_history
, which is overridden by this variable. Setting the value
to an empty string (""
or " "
) disables persistent REPL history.
NODE_EXTRA_CA_CERTS=file
#
When set, the well known "root" CAs (like VeriSign) will be extended with the
extra certificates in file
. The file should consist of one or more trusted
certificates in PEM format. A message will be emitted (once) with
process.emitWarning()
if the file is missing or
malformed, but any errors are otherwise ignored.
Note that neither the well known nor extra certificates are used when the ca
options property is explicitly specified for a TLS or HTTPS client or server.
OPENSSL_CONF=file
#
Load an OpenSSL configuration file on startup. Among other uses, this can be
used to enable FIPS-compliant crypto if Node.js is built with ./configure
--openssl-fips
.
If the --openssl-config
command line option is used, the environment
variable is ignored.
SSL_CERT_DIR=dir
#
If --use-openssl-ca
is enabled, this overrides and sets OpenSSL's directory
containing trusted certificates.
Note: Be aware that unless the child environment is explicitly set, this evironment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.
SSL_CERT_FILE=file
#
If --use-openssl-ca
is enabled, this overrides and sets OpenSSL's file
containing trusted certificates.
Note: Be aware that unless the child environment is explicitly set, this evironment variable will be inherited by any child processes, and if they use OpenSSL, it may cause them to trust the same CAs as node.
NODE_REDIRECT_WARNINGS=file
#
When set, process warnings will be emitted to the given file instead of
printing to stderr. The file will be created if it does not exist, and will be
appended to if it does. If an error occurs while attempting to write the
warning to the file, the warning will be written to stderr instead. This is
equivalent to using the --redirect-warnings=file
command-line flag.
Console#
Stability: 2 - Stable
The console
module provides a simple debugging console that is similar to the
JavaScript console mechanism provided by web browsers.
The module exports two specific components:
- A
Console
class with methods such asconsole.log()
,console.error()
andconsole.warn()
that can be used to write to any Node.js stream. - A global
console
instance configured to write toprocess.stdout
andprocess.stderr
. The globalconsole
can be used without callingrequire('console')
.
Warning: The global console object's methods are neither consistently synchronous like the browser APIs they resemble, nor are they consistently asynchronous like all other Node.js streams. See the note on process I/O for more information.
Example using the global console
:
console.log('hello world');
// Prints: hello world, to stdout
console.log('hello %s', 'world');
// Prints: hello world, to stdout
console.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to stderr
const name = 'Will Robinson';
console.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to stderr
Example using the Console
class:
const out = getStreamSomehow();
const err = getStreamSomehow();
const myConsole = new console.Console(out, err);
myConsole.log('hello world');
// Prints: hello world, to out
myConsole.log('hello %s', 'world');
// Prints: hello world, to out
myConsole.error(new Error('Whoops, something bad happened'));
// Prints: [Error: Whoops, something bad happened], to err
const name = 'Will Robinson';
myConsole.warn(`Danger ${name}! Danger!`);
// Prints: Danger Will Robinson! Danger!, to err
Class: Console#
The Console
class can be used to create a simple logger with configurable
output streams and can be accessed using either require('console').Console
or console.Console
(or their destructured counterparts):
const { Console } = require('console');
const { Console } = console;
new Console(stdout[, stderr])#
stdout
<Writable>stderr
<Writable>
Creates a new Console
by passing one or two writable stream instances.
stdout
is a writable stream to print log or info output. stderr
is used for warning or error output. If stderr
is not passed, warning and error
output will be sent to stdout
.
const output = fs.createWriteStream('./stdout.log');
const errorOutput = fs.createWriteStream('./stderr.log');
// custom simple logger
const logger = new Console(output, errorOutput);
// use it like console
const count = 5;
logger.log('count: %d', count);
// in stdout.log: count 5
The global console
is a special Console
whose output is sent to
process.stdout
and process.stderr
. It is equivalent to calling:
new Console(process.stdout, process.stderr);
console.assert(value[, message][, ...args])#
value
<any>message
<any>...args
<any>
A simple assertion test that verifies whether value
is truthy. If it is not,
an AssertionError
is thrown. If provided, the error message
is formatted
using util.format()
and used as the error message.
console.assert(true, 'does nothing');
// OK
console.assert(false, 'Whoops %s', 'didn\'t work');
// AssertionError: Whoops didn't work
Note: The console.assert()
method is implemented differently in Node.js
than the console.assert()
method available in browsers.
Specifically, in browsers, calling console.assert()
with a falsy
assertion will cause the message
to be printed to the console without
interrupting execution of subsequent code. In Node.js, however, a falsy
assertion will cause an AssertionError
to be thrown.
Functionality approximating that implemented by browsers can be implemented
by extending Node.js' console
and overriding the console.assert()
method.
In the following example, a simple module is created that extends and overrides
the default behavior of console
in Node.js.
'use strict';
// Creates a simple extension of console with a
// new impl for assert without monkey-patching.
const myConsole = Object.create(console, {
assert: {
value: function assert(assertion, message, ...args) {
try {
console.assert(assertion, message, ...args);
} catch (err) {
console.error(err.stack);
}
},
configurable: true,
enumerable: true,
writable: true,
},
});
module.exports = myConsole;
This can then be used as a direct replacement for the built in console:
const console = require('./myConsole');
console.assert(false, 'this message will print, but no error thrown');
console.log('this will also print');
console.dir(obj[, options])#
Uses util.inspect()
on obj
and prints the resulting string to stdout
.
This function bypasses any custom inspect()
function defined on obj
. An
optional options
object may be passed to alter certain aspects of the
formatted string:
showHidden
- iftrue
then the object's non-enumerable and symbol properties will be shown too. Defaults tofalse
.depth
- tellsutil.inspect()
how many times to recurse while formatting the object. This is useful for inspecting large complicated objects. Defaults to2
. To make it recurse indefinitely, passnull
.colors
- iftrue
, then the output will be styled with ANSI color codes. Defaults tofalse
. Colors are customizable; see customizingutil.inspect()
colors.
console.error([data][, ...args])#
data
<any>...args
<any>
Prints to stderr
with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3) (the arguments are all passed to
util.format()
).
const code = 5;
console.error('error #%d', code);
// Prints: error #5, to stderr
console.error('error', code);
// Prints: error 5, to stderr
If formatting elements (e.g. %d
) are not found in the first string then
util.inspect()
is called on each argument and the resulting string
values are concatenated. See util.format()
for more information.
console.info([data][, ...args])#
data
<any>...args
<any>
The console.info()
function is an alias for console.log()
.
console.log([data][, ...args])#
data
<any>...args
<any>
Prints to stdout
with newline. Multiple arguments can be passed, with the
first used as the primary message and all additional used as substitution
values similar to printf(3) (the arguments are all passed to
util.format()
).
const count = 5;
console.log('count: %d', count);
// Prints: count: 5, to stdout
console.log('count:', count);
// Prints: count: 5, to stdout
See util.format()
for more information.
console.time(label)#
label
<string>
Starts a timer that can be used to compute the duration of an operation. Timers
are identified by a unique label
. Use the same label
when calling
console.timeEnd()
to stop the timer and output the elapsed time in
milliseconds to stdout
. Timer durations are accurate to the sub-millisecond.
console.timeEnd(label)#
label
<string>
Stops a timer that was previously started by calling console.time()
and
prints the result to stdout
:
console.time('100-elements');
for (let i = 0; i < 100; i++) {}
console.timeEnd('100-elements');
// prints 100-elements: 225.438ms
Note: As of Node.js v6.0.0, console.timeEnd()
deletes the timer to avoid
leaking it. On older versions, the timer persisted. This allowed
console.timeEnd()
to be called multiple times for the same label. This
functionality was unintended and is no longer supported.
console.trace([message][, ...args])#
message
<any>...args
<any>
Prints to stderr
the string 'Trace :'
, followed by the util.format()
formatted message and stack trace to the current position in the code.
console.trace('Show me');
// Prints: (stack trace will vary based on where trace is called)
// Trace: Show me
// at repl:2:9
// at REPLServer.defaultEval (repl.js:248:27)
// at bound (domain.js:287:14)
// at REPLServer.runBound [as eval] (domain.js:300:12)
// at REPLServer.<anonymous> (repl.js:412:12)
// at emitOne (events.js:82:20)
// at REPLServer.emit (events.js:169:7)
// at REPLServer.Interface._onLine (readline.js:210:10)
// at REPLServer.Interface._line (readline.js:549:8)
// at REPLServer.Interface._ttyWrite (readline.js:826:14)
console.warn([data][, ...args])#
data
<any>...args
<any>
The console.warn()
function is an alias for console.error()
.
Crypto#
Stability: 2 - Stable
The crypto
module provides cryptographic functionality that includes a set of
wrappers for OpenSSL's hash, HMAC, cipher, decipher, sign and verify functions.
Use require('crypto')
to access this module.
const crypto = require('crypto');
const secret = 'abcdefg';
const hash = crypto.createHmac('sha256', secret)
.update('I love cupcakes')
.digest('hex');
console.log(hash);
// Prints:
// c0fa1bc00531bd78ef38c628449c5102aeabd49b5dc3a2a516ea6ea959d6658e
Determining if crypto support is unavailable#
It is possible for Node.js to be built without including support for the
crypto
module. In such cases, calling require('crypto')
will result in an
error being thrown.
let crypto;
try {
crypto = require('crypto');
} catch (err) {
console.log('crypto support is disabled!');
}
Class: Certificate#
SPKAC is a Certificate Signing Request mechanism originally implemented by
Netscape and now specified formally as part of HTML5's keygen
element.
The crypto
module provides the Certificate
class for working with SPKAC
data. The most common usage is handling output generated by the HTML5
<keygen>
element. Node.js uses OpenSSL's SPKAC implementation internally.
new crypto.Certificate()#
Instances of the Certificate
class can be created using the new
keyword
or by calling crypto.Certificate()
as a function:
const crypto = require('crypto');
const cert1 = new crypto.Certificate();
const cert2 = crypto.Certificate();
certificate.exportChallenge(spkac)#
spkac
<string> | <Buffer> | <TypedArray> | <DataView>- Returns <Buffer> The challenge component of the
spkac
data structure, which includes a public key and a challenge.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const challenge = cert.exportChallenge(spkac);
console.log(challenge.toString('utf8'));
// Prints: the challenge as a UTF8 string
certificate.exportPublicKey(spkac)#
spkac
<string> | <Buffer> | <TypedArray> | <DataView>- Returns <Buffer> The public key component of the
spkac
data structure, which includes a public key and a challenge.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
const publicKey = cert.exportPublicKey(spkac);
console.log(publicKey);
// Prints: the public key as <Buffer ...>
certificate.verifySpkac(spkac)#
spkac
<Buffer> | <TypedArray> | <DataView>- Returns <boolean>
true
if the givenspkac
data structure is valid,false
otherwise.
const cert = require('crypto').Certificate();
const spkac = getSpkacSomehow();
console.log(cert.verifySpkac(Buffer.from(spkac)));
// Prints: true or false
Class: Cipher#
Instances of the Cipher
class are used to encrypt data. The class can be
used in one of two ways:
- As a stream that is both readable and writable, where plain unencrypted data is written to produce encrypted data on the readable side, or
- Using the
cipher.update()
andcipher.final()
methods to produce the encrypted data.
The crypto.createCipher()
or crypto.createCipheriv()
methods are
used to create Cipher
instances. Cipher
objects are not to be created
directly using the new
keyword.
Example: Using Cipher
objects as streams:
const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
let encrypted = '';
cipher.on('readable', () => {
const data = cipher.read();
if (data)
encrypted += data.toString('hex');
});
cipher.on('end', () => {
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
});
cipher.write('some clear text data');
cipher.end();
Example: Using Cipher
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const cipher = crypto.createCipher('aes192', 'a password');
const input = fs.createReadStream('test.js');
const output = fs.createWriteStream('test.enc');
input.pipe(cipher).pipe(output);
Example: Using the cipher.update()
and cipher.final()
methods:
const crypto = require('crypto');
const cipher = crypto.createCipher('aes192', 'a password');
let encrypted = cipher.update('some clear text data', 'utf8', 'hex');
encrypted += cipher.final('hex');
console.log(encrypted);
// Prints: ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504
cipher.final([outputEncoding])#
outputEncoding
<string>
Returns any remaining enciphered contents. If outputEncoding
parameter is one of 'latin1'
, 'base64'
or 'hex'
, a string is returned.
If an outputEncoding
is not provided, a Buffer
is returned.
Once the cipher.final()
method has been called, the Cipher
object can no
longer be used to encrypt data. Attempts to call cipher.final()
more than
once will result in an error being thrown.
cipher.setAAD(buffer)#
buffer
<Buffer>- Returns the <Cipher> for method chaining.
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.setAAD()
method sets the value used for the
additional authenticated data (AAD) input parameter.
The cipher.setAAD()
method must be called before cipher.update()
.
cipher.getAuthTag()#
When using an authenticated encryption mode (only GCM
is currently
supported), the cipher.getAuthTag()
method returns a Buffer
containing
the authentication tag that has been computed from the given data.
The cipher.getAuthTag()
method should only be called after encryption has
been completed using the cipher.final()
method.
cipher.setAutoPadding([autoPadding])#
autoPadding
<boolean> Defaults totrue
.- Returns the <Cipher> for method chaining.
When using block encryption algorithms, the Cipher
class will automatically
add padding to the input data to the appropriate block size. To disable the
default padding call cipher.setAutoPadding(false)
.
When autoPadding
is false
, the length of the entire input data must be a
multiple of the cipher's block size or cipher.final()
will throw an Error.
Disabling automatic padding is useful for non-standard padding, for instance
using 0x0
instead of PKCS padding.
The cipher.setAutoPadding()
method must be called before
cipher.final()
.
cipher.update(data[, inputEncoding][, outputEncoding])#
data
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>outputEncoding
<string>
Updates the cipher with data
. If the inputEncoding
argument is given,
its value must be one of 'utf8'
, 'ascii'
, or 'latin1'
and the data
argument is a string using the specified encoding. If the inputEncoding
argument is not given, data
must be a Buffer
, TypedArray
, or
DataView
. If data
is a Buffer
, TypedArray
, or DataView
, then
inputEncoding
is ignored.
The outputEncoding
specifies the output format of the enciphered
data, and can be 'latin1'
, 'base64'
or 'hex'
. If the outputEncoding
is specified, a string using the specified encoding is returned. If no
outputEncoding
is provided, a Buffer
is returned.
The cipher.update()
method can be called multiple times with new data until
cipher.final()
is called. Calling cipher.update()
after
cipher.final()
will result in an error being thrown.
Class: Decipher#
Instances of the Decipher
class are used to decrypt data. The class can be
used in one of two ways:
- As a stream that is both readable and writable, where plain encrypted data is written to produce unencrypted data on the readable side, or
- Using the
decipher.update()
anddecipher.final()
methods to produce the unencrypted data.
The crypto.createDecipher()
or crypto.createDecipheriv()
methods are
used to create Decipher
instances. Decipher
objects are not to be created
directly using the new
keyword.
Example: Using Decipher
objects as streams:
const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
let decrypted = '';
decipher.on('readable', () => {
const data = decipher.read();
if (data)
decrypted += data.toString('utf8');
});
decipher.on('end', () => {
console.log(decrypted);
// Prints: some clear text data
});
const encrypted =
'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
decipher.write(encrypted, 'hex');
decipher.end();
Example: Using Decipher
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const decipher = crypto.createDecipher('aes192', 'a password');
const input = fs.createReadStream('test.enc');
const output = fs.createWriteStream('test.js');
input.pipe(decipher).pipe(output);
Example: Using the decipher.update()
and decipher.final()
methods:
const crypto = require('crypto');
const decipher = crypto.createDecipher('aes192', 'a password');
const encrypted =
'ca981be48e90867604588e75d04feabb63cc007a8f8ad89b10616ed84d815504';
let decrypted = decipher.update(encrypted, 'hex', 'utf8');
decrypted += decipher.final('utf8');
console.log(decrypted);
// Prints: some clear text data
decipher.final([outputEncoding])#
outputEncoding
<string>
Returns any remaining deciphered contents. If outputEncoding
parameter is one of 'latin1'
, 'ascii'
or 'utf8'
, a string is returned.
If an outputEncoding
is not provided, a Buffer
is returned.
Once the decipher.final()
method has been called, the Decipher
object can
no longer be used to decrypt data. Attempts to call decipher.final()
more
than once will result in an error being thrown.
decipher.setAAD(buffer)#
buffer
<Buffer> | <TypedArray> | <DataView>- Returns the <Cipher> for method chaining.
When using an authenticated encryption mode (only GCM
is currently
supported), the decipher.setAAD()
method sets the value used for the
additional authenticated data (AAD) input parameter.
The decipher.setAAD()
method must be called before decipher.update()
.
decipher.setAuthTag(buffer)#
buffer
<Buffer> | <TypedArray> | <DataView>- Returns the <Cipher> for method chaining.
When using an authenticated encryption mode (only GCM
is currently
supported), the decipher.setAuthTag()
method is used to pass in the
received authentication tag. If no tag is provided, or if the cipher text
has been tampered with, decipher.final()
with throw, indicating that the
cipher text should be discarded due to failed authentication.
The decipher.setAuthTag()
method must be called before
decipher.final()
.
decipher.setAutoPadding([autoPadding])#
autoPadding
<boolean> Defaults totrue
.- Returns the <Cipher> for method chaining.
When data has been encrypted without standard block padding, calling
decipher.setAutoPadding(false)
will disable automatic padding to prevent
decipher.final()
from checking for and removing padding.
Turning auto padding off will only work if the input data's length is a multiple of the ciphers block size.
The decipher.setAutoPadding()
method must be called before
decipher.final()
.
decipher.update(data[, inputEncoding][, outputEncoding])#
data
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>outputEncoding
<string>
Updates the decipher with data
. If the inputEncoding
argument is given,
its value must be one of 'latin1'
, 'base64'
, or 'hex'
and the data
argument is a string using the specified encoding. If the inputEncoding
argument is not given, data
must be a Buffer
. If data
is a
Buffer
then inputEncoding
is ignored.
The outputEncoding
specifies the output format of the enciphered
data, and can be 'latin1'
, 'ascii'
or 'utf8'
. If the outputEncoding
is specified, a string using the specified encoding is returned. If no
outputEncoding
is provided, a Buffer
is returned.
The decipher.update()
method can be called multiple times with new data until
decipher.final()
is called. Calling decipher.update()
after
decipher.final()
will result in an error being thrown.
Class: DiffieHellman#
The DiffieHellman
class is a utility for creating Diffie-Hellman key
exchanges.
Instances of the DiffieHellman
class can be created using the
crypto.createDiffieHellman()
function.
const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createDiffieHellman(2048);
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createDiffieHellman(alice.getPrime(), alice.getGenerator());
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
// OK
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
diffieHellman.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])#
otherPublicKey
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>outputEncoding
<string>
Computes the shared secret using otherPublicKey
as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using the specified inputEncoding
, and secret is
encoded using specified outputEncoding
. Encodings can be
'latin1'
, 'hex'
, or 'base64'
. If the inputEncoding
is not
provided, otherPublicKey
is expected to be a Buffer
,
TypedArray
, or DataView
.
If outputEncoding
is given a string is returned; otherwise, a
Buffer
is returned.
diffieHellman.generateKeys([encoding])#
encoding
<string>
Generates private and public Diffie-Hellman key values, and returns
the public key in the specified encoding
. This key should be
transferred to the other party. Encoding can be 'latin1'
, 'hex'
,
or 'base64'
. If encoding
is provided a string is returned; otherwise a
Buffer
is returned.
diffieHellman.getGenerator([encoding])#
encoding
<string>
Returns the Diffie-Hellman generator in the specified encoding
, which can
be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a string is
returned; otherwise a Buffer
is returned.
diffieHellman.getPrime([encoding])#
encoding
<string>
Returns the Diffie-Hellman prime in the specified encoding
, which can
be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a string is
returned; otherwise a Buffer
is returned.
diffieHellman.getPrivateKey([encoding])#
encoding
<string>
Returns the Diffie-Hellman private key in the specified encoding
,
which can be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a
string is returned; otherwise a Buffer
is returned.
diffieHellman.getPublicKey([encoding])#
encoding
<string>
Returns the Diffie-Hellman public key in the specified encoding
, which
can be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided a
string is returned; otherwise a Buffer
is returned.
diffieHellman.setPrivateKey(privateKey[, encoding])#
privateKey
<string> | <Buffer> | <TypedArray> | <DataView>encoding
<string>
Sets the Diffie-Hellman private key. If the encoding
argument is provided
and is either 'latin1'
, 'hex'
, or 'base64'
, privateKey
is expected
to be a string. If no encoding
is provided, privateKey
is expected
to be a Buffer
, TypedArray
, or DataView
.
diffieHellman.setPublicKey(publicKey[, encoding])#
publicKey
<string> | <Buffer> | <TypedArray> | <DataView>encoding
<string>
Sets the Diffie-Hellman public key. If the encoding
argument is provided
and is either 'latin1'
, 'hex'
or 'base64'
, publicKey
is expected
to be a string. If no encoding
is provided, publicKey
is expected
to be a Buffer
, TypedArray
, or DataView
.
diffieHellman.verifyError#
A bit field containing any warnings and/or errors resulting from a check
performed during initialization of the DiffieHellman
object.
The following values are valid for this property (as defined in constants
module):
DH_CHECK_P_NOT_SAFE_PRIME
DH_CHECK_P_NOT_PRIME
DH_UNABLE_TO_CHECK_GENERATOR
DH_NOT_SUITABLE_GENERATOR
Class: ECDH#
The ECDH
class is a utility for creating Elliptic Curve Diffie-Hellman (ECDH)
key exchanges.
Instances of the ECDH
class can be created using the
crypto.createECDH()
function.
const crypto = require('crypto');
const assert = require('assert');
// Generate Alice's keys...
const alice = crypto.createECDH('secp521r1');
const aliceKey = alice.generateKeys();
// Generate Bob's keys...
const bob = crypto.createECDH('secp521r1');
const bobKey = bob.generateKeys();
// Exchange and generate the secret...
const aliceSecret = alice.computeSecret(bobKey);
const bobSecret = bob.computeSecret(aliceKey);
assert.strictEqual(aliceSecret.toString('hex'), bobSecret.toString('hex'));
// OK
ecdh.computeSecret(otherPublicKey[, inputEncoding][, outputEncoding])#
otherPublicKey
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>outputEncoding
<string>
Computes the shared secret using otherPublicKey
as the other
party's public key and returns the computed shared secret. The supplied
key is interpreted using specified inputEncoding
, and the returned secret
is encoded using the specified outputEncoding
. Encodings can be
'latin1'
, 'hex'
, or 'base64'
. If the inputEncoding
is not
provided, otherPublicKey
is expected to be a Buffer
, TypedArray
, or
DataView
.
If outputEncoding
is given a string will be returned; otherwise a
Buffer
is returned.
ecdh.generateKeys([encoding[, format]])#
Generates private and public EC Diffie-Hellman key values, and returns
the public key in the specified format
and encoding
. This key should be
transferred to the other party.
The format
argument specifies point encoding and can be 'compressed'
or
'uncompressed'
. If format
is not specified, the point will be returned in
'uncompressed'
format.
The encoding
argument can be 'latin1'
, 'hex'
, or 'base64'
. If
encoding
is provided a string is returned; otherwise a Buffer
is returned.
ecdh.getPrivateKey([encoding])#
encoding
<string>
Returns the EC Diffie-Hellman private key in the specified encoding
,
which can be 'latin1'
, 'hex'
, or 'base64'
. If encoding
is provided
a string is returned; otherwise a Buffer
is returned.
ecdh.getPublicKey([encoding][, format])#
Returns the EC Diffie-Hellman public key in the specified encoding
and
format
.
The format
argument specifies point encoding and can be 'compressed'
or
'uncompressed'
. If format
is not specified the point will be returned in
'uncompressed'
format.
The encoding
argument can be 'latin1'
, 'hex'
, or 'base64'
. If
encoding
is specified, a string is returned; otherwise a Buffer
is
returned.
ecdh.setPrivateKey(privateKey[, encoding])#
privateKey
<string> | <Buffer> | <TypedArray> | <DataView>encoding
<string>
Sets the EC Diffie-Hellman private key. The encoding
can be 'latin1'
,
'hex'
or 'base64'
. If encoding
is provided, privateKey
is expected
to be a string; otherwise privateKey
is expected to be a Buffer
,
TypedArray
, or DataView
.
If privateKey
is not valid for the curve specified when the ECDH
object was
created, an error is thrown. Upon setting the private key, the associated
public point (key) is also generated and set in the ECDH object.
ecdh.setPublicKey(publicKey[, encoding])#
Stability: 0 - Deprecated
publicKey
<string> | <Buffer> | <TypedArray> | <DataView>encoding
<string>
Sets the EC Diffie-Hellman public key. Key encoding can be 'latin1'
,
'hex'
or 'base64'
. If encoding
is provided publicKey
is expected to
be a string; otherwise a Buffer
, TypedArray
, or DataView
is expected.
Note that there is not normally a reason to call this method because ECDH
only requires a private key and the other party's public key to compute the
shared secret. Typically either ecdh.generateKeys()
or
ecdh.setPrivateKey()
will be called. The ecdh.setPrivateKey()
method
attempts to generate the public point/key associated with the private key being
set.
Example (obtaining a shared secret):
const crypto = require('crypto');
const alice = crypto.createECDH('secp256k1');
const bob = crypto.createECDH('secp256k1');
// Note: This is a shortcut way to specify one of Alice's previous private
// keys. It would be unwise to use such a predictable private key in a real
// application.
alice.setPrivateKey(
crypto.createHash('sha256').update('alice', 'utf8').digest()
);
// Bob uses a newly generated cryptographically strong
// pseudorandom key pair
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
// aliceSecret and bobSecret should be the same shared secret value
console.log(aliceSecret === bobSecret);
Class: Hash#
The Hash
class is a utility for creating hash digests of data. It can be
used in one of two ways:
- As a stream that is both readable and writable, where data is written to produce a computed hash digest on the readable side, or
- Using the
hash.update()
andhash.digest()
methods to produce the computed hash.
The crypto.createHash()
method is used to create Hash
instances. Hash
objects are not to be created directly using the new
keyword.
Example: Using Hash
objects as streams:
const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.on('readable', () => {
const data = hash.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
}
});
hash.write('some data to hash');
hash.end();
Example: Using Hash
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream('test.js');
input.pipe(hash).pipe(process.stdout);
Example: Using the hash.update()
and hash.digest()
methods:
const crypto = require('crypto');
const hash = crypto.createHash('sha256');
hash.update('some data to hash');
console.log(hash.digest('hex'));
// Prints:
// 6a2da20943931e9834fc12cfe5bb47bbd9ae43489a30726962b576f4e3993e50
hash.digest([encoding])#
encoding
<string>
Calculates the digest of all of the data passed to be hashed (using the
hash.update()
method). The encoding
can be 'hex'
, 'latin1'
or
'base64'
. If encoding
is provided a string will be returned; otherwise
a Buffer
is returned.
The Hash
object can not be used again after hash.digest()
method has been
called. Multiple calls will cause an error to be thrown.
hash.update(data[, inputEncoding])#
data
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>
Updates the hash content with the given data
, the encoding of which
is given in inputEncoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
, TypedArray
, or
DataView
, then inputEncoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Hmac#
The Hmac
Class is a utility for creating cryptographic HMAC digests. It can
be used in one of two ways:
- As a stream that is both readable and writable, where data is written to produce a computed HMAC digest on the readable side, or
- Using the
hmac.update()
andhmac.digest()
methods to produce the computed HMAC digest.
The crypto.createHmac()
method is used to create Hmac
instances. Hmac
objects are not to be created directly using the new
keyword.
Example: Using Hmac
objects as streams:
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.on('readable', () => {
const data = hmac.read();
if (data) {
console.log(data.toString('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
}
});
hmac.write('some data to hash');
hmac.end();
Example: Using Hmac
and piped streams:
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream('test.js');
input.pipe(hmac).pipe(process.stdout);
Example: Using the hmac.update()
and hmac.digest()
methods:
const crypto = require('crypto');
const hmac = crypto.createHmac('sha256', 'a secret');
hmac.update('some data to hash');
console.log(hmac.digest('hex'));
// Prints:
// 7fd04df92f636fd450bc841c9418e5825c17f33ad9c87c518115a45971f7f77e
hmac.digest([encoding])#
encoding
<string>
Calculates the HMAC digest of all of the data passed using hmac.update()
.
The encoding
can be 'hex'
, 'latin1'
or 'base64'
. If encoding
is
provided a string is returned; otherwise a Buffer
is returned;
The Hmac
object can not be used again after hmac.digest()
has been
called. Multiple calls to hmac.digest()
will result in an error being thrown.
hmac.update(data[, inputEncoding])#
data
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>
Updates the Hmac
content with the given data
, the encoding of which
is given in inputEncoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
, TypedArray
, or
DataView
, then inputEncoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Sign#
The Sign
Class is a utility for generating signatures. It can be used in one
of two ways:
- As a writable stream, where data to be signed is written and the
sign.sign()
method is used to generate and return the signature, or - Using the
sign.update()
andsign.sign()
methods to produce the signature.
The crypto.createSign()
method is used to create Sign
instances. Sign
objects are not to be created directly using the new
keyword.
Example: Using Sign
objects as streams:
const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.write('some data to sign');
sign.end();
const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature
Example: Using the sign.update()
and sign.sign()
methods:
const crypto = require('crypto');
const sign = crypto.createSign('RSA-SHA256');
sign.update('some data to sign');
const privateKey = getPrivateKeySomehow();
console.log(sign.sign(privateKey, 'hex'));
// Prints: the calculated signature
A Sign
instance can also be created by just passing in the digest
algorithm name, in which case OpenSSL will infer the full signature algorithm
from the type of the PEM-formatted private key, including algorithms that
do not have directly exposed name constants, e.g. 'ecdsa-with-SHA256'.
Example: signing using ECDSA with SHA256
const crypto = require('crypto');
const sign = crypto.createSign('sha256');
sign.update('some data to sign');
const privateKey =
`-----BEGIN EC PRIVATE KEY-----
MHcCAQEEIF+jnWY1D5kbVYDNvxxo/Y+ku2uJPDwS0r/VuPZQrjjVoAoGCCqGSM49
AwEHoUQDQgAEurOxfSxmqIRYzJVagdZfMMSjRNNhB8i3mXyIMq704m2m52FdfKZ2
pQhByd5eyj3lgZ7m7jbchtdgyOF8Io/1ng==
-----END EC PRIVATE KEY-----`;
console.log(sign.sign(privateKey).toString('hex'));
sign.sign(privateKey[, outputFormat])#
Calculates the signature on all the data passed through using either
sign.update()
or sign.write()
.
The privateKey
argument can be an object or a string. If privateKey
is a
string, it is treated as a raw key with no passphrase. If privateKey
is an
object, it must contain one or more of the following properties:
key
: <string> - PEM encoded private key (required)passphrase
: <string> - passphrase for the private keypadding
: <integer> - Optional padding value for RSA, one of the following:crypto.constants.RSA_PKCS1_PADDING
(default)crypto.constants.RSA_PKCS1_PSS_PADDING
Note that
RSA_PKCS1_PSS_PADDING
will use MGF1 with the same hash function used to sign the message as specified in section 3.1 of RFC 4055.saltLength
: <integer> - salt length for when padding isRSA_PKCS1_PSS_PADDING
. The special valuecrypto.constants.RSA_PSS_SALTLEN_DIGEST
sets the salt length to the digest size,crypto.constants.RSA_PSS_SALTLEN_MAX_SIGN
(default) sets it to the maximum permissible value.
The outputFormat
can specify one of 'latin1'
, 'hex'
or 'base64'
. If
outputFormat
is provided a string is returned; otherwise a Buffer
is
returned.
The Sign
object can not be again used after sign.sign()
method has been
called. Multiple calls to sign.sign()
will result in an error being thrown.
sign.update(data[, inputEncoding])#
data
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>
Updates the Sign
content with the given data
, the encoding of which
is given in inputEncoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
, TypedArray
, or
DataView
, then inputEncoding
is ignored.
This can be called many times with new data as it is streamed.
Class: Verify#
The Verify
class is a utility for verifying signatures. It can be used in one
of two ways:
- As a writable stream where written data is used to validate against the supplied signature, or
- Using the
verify.update()
andverify.verify()
methods to verify the signature.
The crypto.createVerify()
method is used to create Verify
instances.
Verify
objects are not to be created directly using the new
keyword.
Example: Using Verify
objects as streams:
const crypto = require('crypto');
const verify = crypto.createVerify('RSA-SHA256');
verify.write('some data to sign');
verify.end();
const publicKey = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(publicKey, signature));
// Prints: true or false
Example: Using the verify.update()
and verify.verify()
methods:
const crypto = require('crypto');
const verify = crypto.createVerify('RSA-SHA256');
verify.update('some data to sign');
const publicKey = getPublicKeySomehow();
const signature = getSignatureToVerify();
console.log(verify.verify(publicKey, signature));
// Prints: true or false
verifier.update(data[, inputEncoding])#
data
<string> | <Buffer> | <TypedArray> | <DataView>inputEncoding
<string>
Updates the Verify
content with the given data
, the encoding of which
is given in inputEncoding
and can be 'utf8'
, 'ascii'
or
'latin1'
. If encoding
is not provided, and the data
is a string, an
encoding of 'utf8'
is enforced. If data
is a Buffer
, TypedArray
, or
DataView
, then inputEncoding
is ignored.
This can be called many times with new data as it is streamed.
verifier.verify(object, signature[, signatureFormat])#
object
<string> | <Object>signature
<string> | <Buffer> | <TypedArray> | <DataView>signatureFormat
<string>
Verifies the provided data using the given object
and signature
.
The object
argument can be either a string containing a PEM encoded object,
which can be an RSA public key, a DSA public key, or an X.509 certificate,
or an object with one or more of the following properties:
key
: <string> - PEM encoded private key (required)padding
: <integer> - Optional padding value for RSA, one of the following:crypto.constants.RSA_PKCS1_PADDING
(default)crypto.constants.RSA_PKCS1_PSS_PADDING
Note that
RSA_PKCS1_PSS_PADDING
will use MGF1 with the same hash function used to verify the message as specified in section 3.1 of RFC 4055.saltLength
: <integer> - salt length for when padding isRSA_PKCS1_PSS_PADDING
. The special valuecrypto.constants.RSA_PSS_SALTLEN_DIGEST
sets the salt length to the digest size,crypto.constants.RSA_PSS_SALTLEN_AUTO
(default) causes it to be determined automatically.
The signature
argument is the previously calculated signature for the data, in
the signatureFormat
which can be 'latin1'
, 'hex'
or 'base64'
.
If a signatureFormat
is specified, the signature
is expected to be a
string; otherwise signature
is expected to be a Buffer
,
TypedArray
, or DataView
.
Returns true
or false
depending on the validity of the signature for
the data and public key.
The verifier
object can not be used again after verify.verify()
has been
called. Multiple calls to verify.verify()
will result in an error being
thrown.
crypto
module methods and properties#
crypto.constants#
Returns an object containing commonly used constants for crypto and security related operations. The specific constants currently defined are described in Crypto Constants.
crypto.DEFAULT_ENCODING#
The default encoding to use for functions that can take either strings
or buffers. The default value is 'buffer'
, which makes methods
default to Buffer
objects.
The crypto.DEFAULT_ENCODING
mechanism is provided for backwards compatibility
with legacy programs that expect 'latin1'
to be the default encoding.
New applications should expect the default to be 'buffer'
. This property may
become deprecated in a future Node.js release.
crypto.fips#
Property for checking and controlling whether a FIPS compliant crypto provider is currently in use. Setting to true requires a FIPS build of Node.js.
crypto.createCipher(algorithm, password)#
algorithm
<string>password
<string> | <Buffer> | <TypedArray> | <DataView>
Creates and returns a Cipher
object that uses the given algorithm
and
password
.
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The password
is used to derive the cipher key and initialization vector (IV).
The value must be either a 'latin1'
encoded string, a Buffer
, a
TypedArray
, or a DataView
.
The implementation of crypto.createCipher()
derives keys using the OpenSSL
function EVP_BytesToKey
with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.
In line with OpenSSL's recommendation to use pbkdf2 instead of
EVP_BytesToKey
it is recommended that developers derive a key and IV on
their own using crypto.pbkdf2()
and to use crypto.createCipheriv()
to create the Cipher
object.
crypto.createCipheriv(algorithm, key, iv)#
algorithm
<string>key
<string> | <Buffer> | <TypedArray> | <DataView>iv
<string> | <Buffer> | <TypedArray> | <DataView>
Creates and returns a Cipher
object, with the given algorithm
, key
and
initialization vector (iv
).
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The key
is the raw key used by the algorithm
and iv
is an
initialization vector. Both arguments must be 'utf8'
encoded strings,
Buffers, TypedArray
, or DataView
s.
crypto.createCredentials(details)#
Stability: 0 - Deprecated: Use tls.createSecureContext()
instead.
details
<Object> Identical totls.createSecureContext()
.
The crypto.createCredentials()
method is a deprecated function for creating
and returning a tls.SecureContext
. It should not be used. Replace it with
tls.createSecureContext()
which has the exact same arguments and return
value.
Returns a tls.SecureContext
, as-if tls.createSecureContext()
had been
called.
crypto.createDecipher(algorithm, password)#
algorithm
<string>password
<string> | <Buffer> | <TypedArray> | <DataView>
Creates and returns a Decipher
object that uses the given algorithm
and
password
(key).
The implementation of crypto.createDecipher()
derives keys using the OpenSSL
function EVP_BytesToKey
with the digest algorithm set to MD5, one
iteration, and no salt. The lack of salt allows dictionary attacks as the same
password always creates the same key. The low iteration count and
non-cryptographically secure hash algorithm allow passwords to be tested very
rapidly.
In line with OpenSSL's recommendation to use pbkdf2 instead of
EVP_BytesToKey
it is recommended that developers derive a key and IV on
their own using crypto.pbkdf2()
and to use crypto.createDecipheriv()
to create the Decipher
object.
crypto.createDecipheriv(algorithm, key, iv)#
algorithm
<string>key
<string> | <Buffer> | <TypedArray> | <DataView>iv
<string> | <Buffer> | <TypedArray> | <DataView>
Creates and returns a Decipher
object that uses the given algorithm
, key
and initialization vector (iv
).
The algorithm
is dependent on OpenSSL, examples are 'aes192'
, etc. On
recent OpenSSL releases, openssl list-cipher-algorithms
will display the
available cipher algorithms.
The key
is the raw key used by the algorithm
and iv
is an
initialization vector. Both arguments must be 'utf8'
encoded strings or
buffers.
crypto.createDiffieHellman(prime[, primeEncoding][, generator][, generatorEncoding])#
prime
<string> | <Buffer> | <TypedArray> | <DataView>primeEncoding
<string>generator
<number> | <string> | <Buffer> | <TypedArray> | <DataView> Defaults to2
.generatorEncoding
<string>
Creates a DiffieHellman
key exchange object using the supplied prime
and an
optional specific generator
.
The generator
argument can be a number, string, or Buffer
. If
generator
is not specified, the value 2
is used.
The primeEncoding
and generatorEncoding
arguments can be 'latin1'
,
'hex'
, or 'base64'
.
If primeEncoding
is specified, prime
is expected to be a string; otherwise
a Buffer
, TypedArray
, or DataView
is expected.
If generatorEncoding
is specified, generator
is expected to be a string;
otherwise a number, Buffer
, TypedArray
, or DataView
is expected.
crypto.createDiffieHellman(primeLength[, generator])#
primeLength
<number>generator
<number> | <string> | <Buffer> | <TypedArray> | <DataView> Defaults to2
.
Creates a DiffieHellman
key exchange object and generates a prime of
primeLength
bits using an optional specific numeric generator
.
If generator
is not specified, the value 2
is used.
crypto.createECDH(curveName)#
curveName
<string>
Creates an Elliptic Curve Diffie-Hellman (ECDH
) key exchange object using a
predefined curve specified by the curveName
string. Use
crypto.getCurves()
to obtain a list of available curve names. On recent
OpenSSL releases, openssl ecparam -list_curves
will also display the name
and description of each available elliptic curve.
crypto.createHash(algorithm)#
algorithm
<string>
Creates and returns a Hash
object that can be used to generate hash digests
using the given algorithm
.
The algorithm
is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are 'sha256'
, 'sha512'
, etc.
On recent releases of OpenSSL, openssl list-message-digest-algorithms
will
display the available digest algorithms.
Example: generating the sha256 sum of a file
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hash = crypto.createHash('sha256');
const input = fs.createReadStream(filename);
input.on('readable', () => {
const data = input.read();
if (data)
hash.update(data);
else {
console.log(`${hash.digest('hex')} ${filename}`);
}
});
crypto.createHmac(algorithm, key)#
algorithm
<string>key
<string> | <Buffer> | <TypedArray> | <DataView>
Creates and returns an Hmac
object that uses the given algorithm
and key
.
The algorithm
is dependent on the available algorithms supported by the
version of OpenSSL on the platform. Examples are 'sha256'
, 'sha512'
, etc.
On recent releases of OpenSSL, openssl list-message-digest-algorithms
will
display the available digest algorithms.
The key
is the HMAC key used to generate the cryptographic HMAC hash.
Example: generating the sha256 HMAC of a file
const filename = process.argv[2];
const crypto = require('crypto');
const fs = require('fs');
const hmac = crypto.createHmac('sha256', 'a secret');
const input = fs.createReadStream(filename);
input.on('readable', () => {
const data = input.read();
if (data)
hmac.update(data);
else {
console.log(`${hmac.digest('hex')} ${filename}`);
}
});
crypto.createSign(algorithm)#
algorithm
<string>
Creates and returns a Sign
object that uses the given algorithm
.
Use crypto.getHashes()
to obtain an array of names of the available
signing algorithms.
crypto.createVerify(algorithm)#
algorithm
<string>
Creates and returns a Verify
object that uses the given algorithm.
Use crypto.getHashes()
to obtain an array of names of the available
signing algorithms.
crypto.getCiphers()#
Returns an array with the names of the supported cipher algorithms.
Example:
const ciphers = crypto.getCiphers();
console.log(ciphers); // ['aes-128-cbc', 'aes-128-ccm', ...]
crypto.getCurves()#
Returns an array with the names of the supported elliptic curves.
Example:
const curves = crypto.getCurves();
console.log(curves); // ['Oakley-EC2N-3', 'Oakley-EC2N-4', ...]
crypto.getDiffieHellman(groupName)#
groupName
<string>
Creates a predefined DiffieHellman
key exchange object. The
supported groups are: 'modp1'
, 'modp2'
, 'modp5'
(defined in
RFC 2412, but see Caveats) and 'modp14'
, 'modp15'
,
'modp16'
, 'modp17'
, 'modp18'
(defined in RFC 3526). The
returned object mimics the interface of objects created by
crypto.createDiffieHellman()
, but will not allow changing
the keys (with diffieHellman.setPublicKey()
for example). The
advantage of using this method is that the parties do not have to
generate nor exchange a group modulus beforehand, saving both processor
and communication time.
Example (obtaining a shared secret):
const crypto = require('crypto');
const alice = crypto.getDiffieHellman('modp14');
const bob = crypto.getDiffieHellman('modp14');
alice.generateKeys();
bob.generateKeys();
const aliceSecret = alice.computeSecret(bob.getPublicKey(), null, 'hex');
const bobSecret = bob.computeSecret(alice.getPublicKey(), null, 'hex');
/* aliceSecret and bobSecret should be the same */
console.log(aliceSecret === bobSecret);
crypto.getHashes()#
Returns an array of the names of the supported hash algorithms,
such as RSA-SHA256
.
Example:
const hashes = crypto.getHashes();
console.log(hashes); // ['DSA', 'DSA-SHA', 'DSA-SHA1', ...]
crypto.pbkdf2(password, salt, iterations, keylen, digest, callback)#
password
<string>salt
<string>iterations
<number>keylen
<number>digest
<string>callback
<Function>
Provides an asynchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by digest
is
applied to derive a key of the requested byte length (keylen
) from the
password
, salt
and iterations
.
The supplied callback
function is called with two arguments: err
and
derivedKey
. If an error occurs, err
will be set; otherwise err
will be
null. The successfully generated derivedKey
will be passed as a Buffer
.
The iterations
argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.
The salt
should also be as unique as possible. It is recommended that the
salts are random and their lengths are greater than 16 bytes. See
NIST SP 800-132 for details.
Example:
const crypto = require('crypto');
crypto.pbkdf2('secret', 'salt', 100000, 512, 'sha512', (err, derivedKey) => {
if (err) throw err;
console.log(derivedKey.toString('hex')); // '3745e48...aa39b34'
});
An array of supported digest functions can be retrieved using
crypto.getHashes()
.
crypto.pbkdf2Sync(password, salt, iterations, keylen, digest)#
Provides a synchronous Password-Based Key Derivation Function 2 (PBKDF2)
implementation. A selected HMAC digest algorithm specified by digest
is
applied to derive a key of the requested byte length (keylen
) from the
password
, salt
and iterations
.
If an error occurs an Error will be thrown, otherwise the derived key will be
returned as a Buffer
.
The iterations
argument must be a number set as high as possible. The
higher the number of iterations, the more secure the derived key will be,
but will take a longer amount of time to complete.
The salt
should also be as unique as possible. It is recommended that the
salts are random and their lengths are greater than 16 bytes. See
NIST SP 800-132 for details.
Example:
const crypto = require('crypto');
const key = crypto.pbkdf2Sync('secret', 'salt', 100000, 512, 'sha512');
console.log(key.toString('hex')); // '3745e48...aa39b34'
An array of supported digest functions can be retrieved using
crypto.getHashes()
.
crypto.privateDecrypt(privateKey, buffer)#
privateKey
<Object> | <string>buffer
<Buffer> | <TypedArray> | <DataView>
Decrypts buffer
with privateKey
.
privateKey
can be an object or a string. If privateKey
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING
.
crypto.privateEncrypt(privateKey, buffer)#
privateKey
<Object> | <string>buffer
<Buffer> | <TypedArray> | <DataView>
Encrypts buffer
with privateKey
.
privateKey
can be an object or a string. If privateKey
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_PADDING
.
crypto.publicDecrypt(publicKey, buffer)#
publicKey
<Object> | <string>buffer
<Buffer> | <TypedArray> | <DataView>
Decrypts buffer
with publicKey
.
publicKey
can be an object or a string. If publicKey
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_PADDING
.
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
crypto.publicEncrypt(publicKey, buffer)#
publicKey
<Object> | <string>buffer
<Buffer> | <TypedArray> | <DataView>
Encrypts the content of buffer
with publicKey
and returns a new
Buffer
with encrypted content.
publicKey
can be an object or a string. If publicKey
is a string, it is
treated as the key with no passphrase and will use RSA_PKCS1_OAEP_PADDING
.
Because RSA public keys can be derived from private keys, a private key may be passed instead of a public key.
crypto.randomBytes(size[, callback])#
size
<number>callback
<Function>
Generates cryptographically strong pseudo-random data. The size
argument
is a number indicating the number of bytes to generate.
If a callback
function is provided, the bytes are generated asynchronously
and the callback
function is invoked with two arguments: err
and buf
.
If an error occurs, err
will be an Error object; otherwise it is null. The
buf
argument is a Buffer
containing the generated bytes.
// Asynchronous
const crypto = require('crypto');
crypto.randomBytes(256, (err, buf) => {
if (err) throw err;
console.log(`${buf.length} bytes of random data: ${buf.toString('hex')}`);
});
If the callback
function is not provided, the random bytes are generated
synchronously and returned as a Buffer
. An error will be thrown if
there is a problem generating the bytes.
// Synchronous
const buf = crypto.randomBytes(256);
console.log(
`${buf.length} bytes of random data: ${buf.toString('hex')}`);
The crypto.randomBytes()
method will block until there is sufficient entropy.
This should normally never take longer than a few milliseconds. The only time
when generating the random bytes may conceivably block for a longer period of
time is right after boot, when the whole system is still low on entropy.
crypto.randomFillSync(buffer[, offset][, size])#
buffer
<Buffer> | <Uint8Array> Must be supplied.offset
<number> Defaults to0
.size
<number> Defaults tobuffer.length - offset
.
Synchronous version of crypto.randomFill()
.
Returns buffer
const buf = Buffer.alloc(10);
console.log(crypto.randomFillSync(buf).toString('hex'));
crypto.randomFillSync(buf, 5);
console.log(buf.toString('hex'));
// The above is equivalent to the following:
crypto.randomFillSync(buf, 5, 5);
console.log(buf.toString('hex'));
crypto.randomFill(buffer[, offset][, size], callback)#
buffer
<Buffer> | <Uint8Array> Must be supplied.offset
<number> Defaults to0
.size
<number> Defaults tobuffer.length - offset
.callback
<Function>function(err, buf) {}
.
This function is similar to crypto.randomBytes()
but requires the first
argument to be a Buffer
that will be filled. It also
requires that a callback is passed in.
If the callback
function is not provided, an error will be thrown.
const buf = Buffer.alloc(10);
crypto.randomFill(buf, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
crypto.randomFill(buf, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
// The above is equivalent to the following:
crypto.randomFill(buf, 5, 5, (err, buf) => {
if (err) throw err;
console.log(buf.toString('hex'));
});
crypto.setEngine(engine[, flags])#
engine
<string>flags
<crypto.constants> Defaults tocrypto.constants.ENGINE_METHOD_ALL
.
Load and set the engine
for some or all OpenSSL functions (selected by flags).
engine
could be either an id or a path to the engine's shared library.
The optional flags
argument uses ENGINE_METHOD_ALL
by default. The flags
is a bit field taking one of or a mix of the following flags (defined in
crypto.constants
):
crypto.constants.ENGINE_METHOD_RSA
crypto.constants.ENGINE_METHOD_DSA
crypto.constants.ENGINE_METHOD_DH
crypto.constants.ENGINE_METHOD_RAND
crypto.constants.ENGINE_METHOD_ECDH
crypto.constants.ENGINE_METHOD_ECDSA
crypto.constants.ENGINE_METHOD_CIPHERS
crypto.constants.ENGINE_METHOD_DIGESTS
crypto.constants.ENGINE_METHOD_STORE
crypto.constants.ENGINE_METHOD_PKEY_METHS
crypto.constants.ENGINE_METHOD_PKEY_ASN1_METHS
crypto.constants.ENGINE_METHOD_ALL
crypto.constants.ENGINE_METHOD_NONE
crypto.timingSafeEqual(a, b)#
a
<Buffer> | <TypedArray> | <DataView>b
<Buffer> | <TypedArray> | <DataView>
Returns true if a
is equal to b
, without leaking timing information that
would allow an attacker to guess one of the values. This is suitable for
comparing HMAC digests or secret values like authentication cookies or
capability urls.
a
and b
must both be Buffer
s, TypedArray
s, or DataView
s, and they
must have the same length.
Note: Use of crypto.timingSafeEqual
does not guarantee that the
surrounding code is timing-safe. Care should be taken to ensure that the
surrounding code does not introduce timing vulnerabilities.
Notes#
Legacy Streams API (pre Node.js v0.10)#
The Crypto module was added to Node.js before there was the concept of a
unified Stream API, and before there were Buffer
objects for handling
binary data. As such, the many of the crypto
defined classes have methods not
typically found on other Node.js classes that implement the streams
API (e.g. update()
, final()
, or digest()
). Also, many methods accepted
and returned 'latin1'
encoded strings by default rather than Buffers. This
default was changed after Node.js v0.8 to use Buffer
objects by default
instead.
Recent ECDH Changes#
Usage of ECDH
with non-dynamically generated key pairs has been simplified.
Now, ecdh.setPrivateKey()
can be called with a preselected private key
and the associated public point (key) will be computed and stored in the object.
This allows code to only store and provide the private part of the EC key pair.
ecdh.setPrivateKey()
now also validates that the private key is valid for
the selected curve.
The ecdh.setPublicKey()
method is now deprecated as its inclusion in the
API is not useful. Either a previously stored private key should be set, which
automatically generates the associated public key, or ecdh.generateKeys()
should be called. The main drawback of using ecdh.setPublicKey()
is that
it can be used to put the ECDH key pair into an inconsistent state.
Support for weak or compromised algorithms#
The crypto
module still supports some algorithms which are already
compromised and are not currently recommended for use. The API also allows
the use of ciphers and hashes with a small key size that are considered to be
too weak for safe use.
Users should take full responsibility for selecting the crypto algorithm and key size according to their security requirements.
Based on the recommendations of NIST SP 800-131A:
- MD5 and SHA-1 are no longer acceptable where collision resistance is required such as digital signatures.
- The key used with RSA, DSA and DH algorithms is recommended to have at least 2048 bits and that of the curve of ECDSA and ECDH at least 224 bits, to be safe to use for several years.
- The DH groups of
modp1
,modp2
andmodp5
have a key size smaller than 2048 bits and are not recommended.
See the reference for other recommendations and details.
Crypto Constants#
The following constants exported by crypto.constants
apply to various uses of
the crypto
, tls
, and https
modules and are generally specific to OpenSSL.
OpenSSL Options#
Constant | Description |
---|---|
SSL_OP_ALL |
Applies multiple bug workarounds within OpenSSL. See https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html for detail. |
SSL_OP_ALLOW_UNSAFE_LEGACY_RENEGOTIATION |
Allows legacy insecure renegotiation between OpenSSL and unpatched clients or servers. See https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html. |
SSL_OP_CIPHER_SERVER_PREFERENCE |
Attempts to use the server's preferences instead of the client's when selecting a cipher. Behavior depends on protocol version. See https://www.openssl.org/docs/man1.0.2/ssl/SSL_CTX_set_options.html. |
SSL_OP_CISCO_ANYCONNECT |
Instructs OpenSSL to use Cisco's "speshul" version of DTLS_BAD_VER. |
SSL_OP_COOKIE_EXCHANGE |
Instructs OpenSSL to turn on cookie exchange. |
SSL_OP_CRYPTOPRO_TLSEXT_BUG |
Instructs OpenSSL to add server-hello extension from an early version of the cryptopro draft. |
SSL_OP_DONT_INSERT_EMPTY_FRAGMENTS |
Instructs OpenSSL to disable a SSL 3.0/TLS 1.0 vulnerability workaround added in OpenSSL 0.9.6d. |
SSL_OP_EPHEMERAL_RSA |
Instructs OpenSSL to always use the tmp_rsa key when performing RSA operations. |
SSL_OP_LEGACY_SERVER_CONNECT |
Allows initial connection to servers that do not support RI. |
SSL_OP_MICROSOFT_BIG_SSLV3_BUFFER |
|
SSL_OP_MICROSOFT_SESS_ID_BUG |
|
SSL_OP_MSIE_SSLV2_RSA_PADDING |
Instructs OpenSSL to disable the workaround for a man-in-the-middle protocol-version vulnerability in the SSL 2.0 server implementation. |
SSL_OP_NETSCAPE_CA_DN_BUG |
|
SSL_OP_NETSCAPE_CHALLENGE_BUG |
|
SSL_OP_NETSCAPE_DEMO_CIPHER_CHANGE_BUG |
|
SSL_OP_NETSCAPE_REUSE_CIPHER_CHANGE_BUG |
|
SSL_OP_NO_COMPRESSION |
Instructs OpenSSL to disable support for SSL/TLS compression. |
SSL_OP_NO_QUERY_MTU |
|
SSL_OP_NO_SESSION_RESUMPTION_ON_RENEGOTIATION |
Instructs OpenSSL to always start a new session when performing renegotiation. |
SSL_OP_NO_SSLv2 |
Instructs OpenSSL to turn off SSL v2 |
SSL_OP_NO_SSLv3 |
Instructs OpenSSL to turn off SSL v3 |
SSL_OP_NO_TICKET |
Instructs OpenSSL to disable use of RFC4507bis tickets. |
SSL_OP_NO_TLSv1 |
Instructs OpenSSL to turn off TLS v1 |
SSL_OP_NO_TLSv1_1 |
Instructs OpenSSL to turn off TLS v1.1 |
SSL_OP_NO_TLSv1_2 |
Instructs OpenSSL to turn off TLS v1.2 | SSL_OP_PKCS1_CHECK_1 |
SSL_OP_PKCS1_CHECK_2 |
|
SSL_OP_SINGLE_DH_USE |
Instructs OpenSSL to always create a new key when using temporary/ephemeral DH parameters. |
SSL_OP_SINGLE_ECDH_USE |
Instructs OpenSSL to always create a new key when using temporary/ephemeral ECDH parameters. | SSL_OP_SSLEAY_080_CLIENT_DH_BUG |
SSL_OP_SSLREF2_REUSE_CERT_TYPE_BUG |
|
SSL_OP_TLS_BLOCK_PADDING_BUG |
|
SSL_OP_TLS_D5_BUG |
|
SSL_OP_TLS_ROLLBACK_BUG |
Instructs OpenSSL to disable version rollback attack detection. |
OpenSSL Engine Constants#
Constant | Description |
---|---|
ENGINE_METHOD_RSA |
Limit engine usage to RSA |
ENGINE_METHOD_DSA |
Limit engine usage to DSA |
ENGINE_METHOD_DH |
Limit engine usage to DH |
ENGINE_METHOD_RAND |
Limit engine usage to RAND |
ENGINE_METHOD_ECDH |
Limit engine usage to ECDH |
ENGINE_METHOD_ECDSA |
Limit engine usage to ECDSA |
ENGINE_METHOD_CIPHERS |
Limit engine usage to CIPHERS |
ENGINE_METHOD_DIGESTS |
Limit engine usage to DIGESTS |
ENGINE_METHOD_STORE |
Limit engine usage to STORE |
ENGINE_METHOD_PKEY_METHS |
Limit engine usage to PKEY_METHDS |
ENGINE_METHOD_PKEY_ASN1_METHS |
Limit engine usage to PKEY_ASN1_METHS |
ENGINE_METHOD_ALL |
|
ENGINE_METHOD_NONE |
Other OpenSSL Constants#
Constant | Description |
---|---|
DH_CHECK_P_NOT_SAFE_PRIME |
|
DH_CHECK_P_NOT_PRIME |
|
DH_UNABLE_TO_CHECK_GENERATOR |
|
DH_NOT_SUITABLE_GENERATOR |
|
NPN_ENABLED |
|
ALPN_ENABLED |
|
RSA_PKCS1_PADDING |
|
RSA_SSLV23_PADDING |
|
RSA_NO_PADDING |
|
RSA_PKCS1_OAEP_PADDING |
|
RSA_X931_PADDING |
|
RSA_PKCS1_PSS_PADDING |
|
RSA_PSS_SALTLEN_DIGEST |
Sets the salt length for RSA_PKCS1_PSS_PADDING to the digest size
when signing or verifying. |
RSA_PSS_SALTLEN_MAX_SIGN |
Sets the salt length for RSA_PKCS1_PSS_PADDING to the maximum
permissible value when signing data. |
RSA_PSS_SALTLEN_AUTO |
Causes the salt length for RSA_PKCS1_PSS_PADDING to be determined
automatically when verifying a signature. |
POINT_CONVERSION_COMPRESSED |
|
POINT_CONVERSION_UNCOMPRESSED |
|
POINT_CONVERSION_HYBRID |
Node.js Crypto Constants#
Constant | Description |
---|---|
defaultCoreCipherList |
Specifies the built-in default cipher list used by Node.js. |
defaultCipherList |
Specifies the active default cipher list used by the current Node.js process. |
Debugger#
Stability: 2 - Stable
Node.js includes an out-of-process debugging utility accessible via a
TCP-based protocol and built-in debugging client. To use it, start Node.js
with the inspect
argument followed by the path to the script to debug; a prompt
will be displayed indicating successful launch of the debugger:
$ node inspect myscript.js
< Debugger listening on ws://127.0.0.1:9229/80e7a814-7cd3-49fb-921a-2e02228cd5ba
< For help see https://nodejs.org/en/docs/inspector
< Debugger attached.
Break on start in myscript.js:1
> 1 (function (exports, require, module, __filename, __dirname) { global.x = 5;
2 setTimeout(() => {
3 console.log('world');
debug>
Node.js's debugger client is not a full-featured debugger, but simple step and inspection are possible.
Inserting the statement debugger;
into the source code of a script will
enable a breakpoint at that position in the code:
// myscript.js
global.x = 5;
setTimeout(() => {
debugger;
console.log('world');
}, 1000);
console.log('hello');
Once the debugger is run, a breakpoint will occur at line 3:
$ node inspect myscript.js
< Debugger listening on ws://127.0.0.1:9229/80e7a814-7cd3-49fb-921a-2e02228cd5ba
< For help see https://nodejs.org/en/docs/inspector
< Debugger attached.
Break on start in myscript.js:1
> 1 (function (exports, require, module, __filename, __dirname) { global.x = 5;
2 setTimeout(() => {
3 debugger;
debug> cont
< hello
break in myscript.js:3
1 (function (exports, require, module, __filename, __dirname) { global.x = 5;
2 setTimeout(() => {
> 3 debugger;
4 console.log('world');
5 }, 1000);
debug> next
break in myscript.js:4
2 setTimeout(() => {
3 debugger;
> 4 console.log('world');
5 }, 1000);
6 console.log('hello');
debug> repl
Press Ctrl + C to leave debug repl
> x
5
> 2+2
4
debug> next
< world
break in myscript.js:5
3 debugger;
4 console.log('world');
> 5 }, 1000);
6 console.log('hello');
7
debug> .exit
The repl
command allows code to be evaluated remotely. The next
command
steps to the next line. Type help
to see what other commands are available.
Pressing enter
without typing a command will repeat the previous debugger
command.
Watchers#
It is possible to watch expression and variable values while debugging. On every breakpoint, each expression from the watchers list will be evaluated in the current context and displayed immediately before the breakpoint's source code listing.
To begin watching an expression, type watch('my_expression')
. The command
watchers
will print the active watchers. To remove a watcher, type
unwatch('my_expression')
.
Command reference#
Stepping#
cont
,c
- Continue executionnext
,n
- Step nextstep
,s
- Step inout
,o
- Step outpause
- Pause running code (like pause button in Developer Tools)
Breakpoints#
setBreakpoint()
,sb()
- Set breakpoint on current linesetBreakpoint(line)
,sb(line)
- Set breakpoint on specific linesetBreakpoint('fn()')
,sb(...)
- Set breakpoint on a first statement in functions bodysetBreakpoint('script.js', 1)
,sb(...)
- Set breakpoint on first line of script.jsclearBreakpoint('script.js', 1)
,cb(...)
- Clear breakpoint in script.js on line 1
It is also possible to set a breakpoint in a file (module) that is not loaded yet:
$ node inspect test/fixtures/break-in-module/main.js
< Debugger listening on ws://127.0.0.1:9229/4e3db158-9791-4274-8909-914f7facf3bd
< For help see https://nodejs.org/en/docs/inspector
< Debugger attached.
Break on start in test/fixtures/break-in-module/main.js:1
> 1 (function (exports, require, module, __filename, __dirname) { const mod = require('./mod.js');
2 mod.hello();
3 mod.hello();
debug> setBreakpoint('mod.js', 22)
Warning: script 'mod.js' was not loaded yet.
debug> c
break in test/fixtures/break-in-module/mod.js:22
20 // USE OR OTHER DEALINGS IN THE SOFTWARE.
21
>22 exports.hello = function() {
23 return 'hello from module';
24 };
debug>
Information#
backtrace
,bt
- Print backtrace of current execution framelist(5)
- List scripts source code with 5 line context (5 lines before and after)watch(expr)
- Add expression to watch listunwatch(expr)
- Remove expression from watch listwatchers
- List all watchers and their values (automatically listed on each breakpoint)repl
- Open debugger's repl for evaluation in debugging script's contextexec expr
- Execute an expression in debugging script's context
Execution control#
run
- Run script (automatically runs on debugger's start)restart
- Restart scriptkill
- Kill script
Various#
scripts
- List all loaded scriptsversion
- Display V8's version
Advanced Usage#
V8 Inspector Integration for Node.js#
V8 Inspector integration allows attaching Chrome DevTools to Node.js instances for debugging and profiling. It uses the Chrome Debugging Protocol.
V8 Inspector can be enabled by passing the --inspect
flag when starting a
Node.js application. It is also possible to supply a custom port with that flag,
e.g. --inspect=9222
will accept DevTools connections on port 9222.
To break on the first line of the application code, pass the --inspect-brk
flag instead of --inspect
.
$ node --inspect index.js
Debugger listening on 127.0.0.1:9229.
To start debugging, open the following URL in Chrome:
chrome-devtools://devtools/bundled/inspector.html?experiments=true&v8only=true&ws=127.0.0.1:9229/dc9010dd-f8b8-4ac5-a510-c1a114ec7d29
(In the example above, the UUID dc9010dd-f8b8-4ac5-a510-c1a114ec7d29 at the end of the URL is generated on the fly, it varies in different debugging sessions.)
Deprecated APIs#
Node.js may deprecate APIs when either: (a) use of the API is considered to be unsafe, (b) an improved alternative API has been made available, or (c) breaking changes to the API are expected in a future major release.
Node.js utilizes three kinds of Deprecations:
- Documentation-only
- Runtime
- End-of-Life
A Documentation-only deprecation is one that is expressed only within the Node.js API docs. These generate no side-effects while running Node.js.
A Runtime deprecation will, by default, generate a process warning that will
be printed to stderr
the first time the deprecated API is used. When the
--throw-deprecation
command-line flag is used, a Runtime deprecation will
cause an error to be thrown.
An End-of-Life deprecation is used to identify code that either has been removed or will soon be removed from Node.js.
Un-deprecation#
From time-to-time the deprecation of an API may be reversed. Such action may happen in either a semver-minor or semver-major release. In such situations, this document will be updated with information relevant to the decision. However, the deprecation identifier will not be modified.
List of Deprecated APIs#
DEP0001: http.OutgoingMessage.prototype.flush#
Type: Runtime
The OutgoingMessage.prototype.flush()
method is deprecated. Use
OutgoingMessage.prototype.flushHeaders()
instead.
DEP0002: require('_linklist')#
Type: Runtime
The _linklist
module is deprecated. Please use a userland alternative.
DEP0003: _writableState.buffer#
Type: Runtime
The _writableState.buffer
property is deprecated. Use the
_writableState.getBuffer()
method instead.
DEP0004: CryptoStream.prototype.readyState#
Type: Documentation-only
The CryptoStream.prototype.readyState
property is deprecated and should not
be used.
DEP0005: Buffer() constructor#
Type: Documentation-only
The Buffer()
function and new Buffer()
constructor are deprecated due to
API usability issues that can potentially lead to accidental security issues.
As an alternative, use of the following methods of constructing Buffer
objects
is strongly recommended:
Buffer.alloc(size[, fill[, encoding]])
- Create aBuffer
with initialized memory.Buffer.allocUnsafe(size)
- Create aBuffer
with uninitialized memory.Buffer.allocUnsafeSlow(size)
- Create aBuffer
with uninitialized memory.Buffer.from(array)
- Create aBuffer
with a copy ofarray
Buffer.from(arrayBuffer[, byteOffset[, length]])
- Create aBuffer
that wraps the givenarrayBuffer
.Buffer.from(buffer)
- Create aBuffer
that copiesbuffer
.Buffer.from(string[, encoding])
- Create aBuffer
that copiesstring
.
DEP0006: child_process options.customFds#
Type: Runtime
Within the child_process
module's spawn()
, fork()
, and exec()
methods, the options.customFds
option is deprecated. The options.stdio
option should be used instead.
DEP0007: cluster worker.suicide#
Type: Runtime
Within the cluster
module, the worker.suicide
property has been
deprecated. Please use worker.exitedAfterDisconnect
instead.
DEP0008: require('constants')#
Type: Documentation-only
The constants
module has been deprecated. When requiring access to constants
relevant to specific Node.js builtin modules, developers should instead refer
to the constants
property exposed by the relevant module. For instance,
require('fs').constants
and require('os').constants
.
DEP0009: crypto.pbkdf2 without digest#
Type: End-of-life
Use of the crypto.pbkdf2()
API without specifying a digest was deprecated
in Node.js 6.0 because the method defaulted to using the non-recommendend
'SHA1'
digest. Previously, a deprecation warning was printed. Starting in
Node.js 8.0.0, calling crypto.pbkdf2()
or crypto.pbkdf2Sync()
with an
undefined digest
will throw a TypeError
.
DEP0010: crypto.createCredentials#
Type: Runtime
The crypto.createCredentials()
API is deprecated. Please use
tls.createSecureContext()
instead.
DEP0011: crypto.Credentials#
Type: Runtime
The crypto.Credentials
class is deprecated. Please use tls.SecureContext
instead.
DEP0012: Domain.dispose#
Type: Runtime
Domain.dispose()
is deprecated. Recover from failed I/O actions
explicitly via error event handlers set on the domain instead.
DEP0013: fs async function without callback#
Type: Runtime
Calling an asynchronous function without a callback is deprecated.
DEP0014: fs.read legacy String interface#
Type: End-of-Life
The fs.read()
legacy String interface is deprecated. Use the Buffer API as
mentioned in the documentation instead.
DEP0015: fs.readSync legacy String interface#
Type: End-of-Life
The fs.readSync()
legacy String interface is deprecated. Use the Buffer
API as mentioned in the documentation instead.
DEP0016: GLOBAL/root#
Type: Runtime
The GLOBAL
and root
aliases for the global
property have been deprecated
and should no longer be used.
DEP0017: Intl.v8BreakIterator#
Type: Runtime
The Intl.v8BreakIterator
is deprecated and will be removed or replaced soon.
DEP0018: Unhandled promise rejections#
Type: Runtime
Unhandled promise rejections are deprecated. In the future, promise rejections that are not handled will terminate the Node.js process with a non-zero exit code.
DEP0019: require('.') resolved outside directory#
Type: Runtime
In certain cases, require('.')
may resolve outside the package directory.
This behavior is deprecated and will be removed in a future major Node.js
release.
DEP0020: Server.connections#
Type: Runtime
The Server.connections
property is deprecated. Please use the
Server.getConnections()
method instead.
DEP0021: Server.listenFD#
Type: Runtime
The Server.listenFD()
method is deprecated. Please use
Server.listen({fd: <number>})
instead.
DEP0022: os.tmpDir()#
Type: Runtime
The os.tmpDir()
API is deprecated. Please use os.tmpdir()
instead.
DEP0023: os.getNetworkInterfaces()#
Type: Runtime
The os.getNetworkInterfaces()
method is deprecated. Please use the
os.networkInterfaces
property instead.
DEP0024: REPLServer.prototype.convertToContext()#
Type: Runtime
The REPLServer.prototype.convertToContext()
API is deprecated and should
not be used.
DEP0025: require('sys')#
Type: Runtime
The sys
module is deprecated. Please use the util
module instead.
DEP0026: util.print()#
Type: Runtime
The util.print()
API is deprecated. Please use console.log()
instead.
DEP0027: util.puts()#
Type: Runtime
The util.puts()
API is deprecated. Please use console.log()
instead.
DEP0028: util.debug()#
Type: Runtime
The util.debug()
API is deprecated. Please use console.error()
instead.
DEP0029: util.error()#
Type: Runtime
The util.error()
API is deprecated. Please use console.error()
instead.
DEP0030: SlowBuffer#
Type: Documentation-only
The SlowBuffer
class has been deprecated. Please use
Buffer.allocUnsafeSlow(size)
instead.
DEP0031: ecdh.setPublicKey()#
Type: Documentation-only
The ecdh.setPublicKey()
method is now deprecated as its inclusion in the
API is not useful.
DEP0032: domain module#
Type: Documentation-only
The domain
module is deprecated and should not be used.
DEP0033: EventEmitter.listenerCount()#
Type: Documentation-only
The EventEmitter.listenerCount(emitter, eventName)
API has been
deprecated. Please use emitter.listenerCount(eventName)
instead.
DEP0034: fs.exists(path, callback)#
Type: Documentation-only
The fs.exists(path, callback)
API has been deprecated. Please use
fs.stat()
or fs.access()
instead.
DEP0035: fs.lchmod(path, mode, callback)#
Type: Documentation-only
The fs.lchmod(path, mode, callback)
API has been deprecated.
DEP0036: fs.lchmodSync(path, mode)#
Type: Documentation-only
The fs.lchmodSync(path, mode)
API has been deprecated.
DEP0037: fs.lchown(path, uid, gid, callback)#
Type: Documentation-only
The fs.lchown(path, uid, gid, callback)
API has been deprecated.
DEP0038: fs.lchownSync(path, uid, gid)#
Type: Documentation-only
The fs.lchownSync(path, uid, gid)
API has been deprecated.
DEP0039: require.extensions#
Type: Documentation-only
The require.extensions
property has been deprecated.
DEP0040: punycode module#
Type: Documentation-only
The punycode
module has been deprecated. Please use a userland alternative
instead.
DEP0041: NODE_REPL_HISTORY_FILE environment variable#
Type: Documentation-only
The NODE_REPL_HISTORY_FILE
environment variable has been deprecated.
DEP0042: tls.CryptoStream#
Type: Documentation-only
The tls.CryptoStream
class has been deprecated. Please use
tls.TLSSocket
instead.
DEP0043: tls.SecurePair#
Type: Documentation-only
The tls.SecurePair
class has been deprecated. Please use
tls.TLSSocket
instead.
DEP0044: util.isArray()#
Type: Documentation-only
The util.isArray()
API has been deprecated. Please use Array.isArray()
instead.
DEP0045: util.isBoolean()#
Type: Documentation-only
The util.isBoolean()
API has been deprecated.
DEP0046: util.isBuffer()#
Type: Documentation-only
The util.isBuffer()
API has been deprecated. Please use
Buffer.isBuffer()
instead.
DEP0047: util.isDate()#
Type: Documentation-only
The util.isDate()
API has been deprecated.
DEP0048: util.isError()#
Type: Documentation-only
The util.isError()
API has been deprecated.
DEP0049: util.isFunction()#
Type: Documentation-only
The util.isFunction()
API has been deprecated.
DEP0050: util.isNull()#
Type: Documentation-only
The util.isNull()
API has been deprecated.
DEP0051: util.isNullOrUndefined()#
Type: Documentation-only
The util.isNullOrUndefined()
API has been deprecated.
DEP0052: util.isNumber()#
Type: Documentation-only
The util.isNumber()
API has been deprecated.
DEP0053 util.isObject()#
Type: Documentation-only
The util.isObject()
API has been deprecated.
DEP0054: util.isPrimitive()#
Type: Documentation-only
The util.isPrimitive()
API has been deprecated.
DEP0055: util.isRegExp()#
Type: Documentation-only
The util.isRegExp()
API has been deprecated.
DEP0056: util.isString()#
Type: Documentation-only
The util.isString()
API has been deprecated.
DEP0057: util.isSymbol()#
Type: Documentation-only
The util.isSymbol()
API has been deprecated.
DEP0058: util.isUndefined()#
Type: Documentation-only
The util.isUndefined()
API has been deprecated.
DEP0059: util.log()#
Type: Documentation-only
The util.log()
API has been deprecated.
DEP0060: util._extend()#
Type: Documentation-only
The util._extend()
API has been deprecated.
DEP0061: fs.SyncWriteStream#
Type: Runtime
The fs.SyncWriteStream
class was never intended to be a publicly accessible
API. No alternative API is available. Please use a userland alternative.
DEP0062: node --debug#
Type: Runtime
--debug
activates the legacy V8 debugger interface, which has been removed as
of V8 5.8. It is replaced by Inspector which is activated with --inspect
instead.
DEP0063: ServerResponse.prototype.writeHeader()#
Type: Documentation-only
The http
module ServerResponse.prototype.writeHeader()
API has been
deprecated. Please use ServerResponse.prototype.writeHead()
instead.
Note: The ServerResponse.prototype.writeHeader()
method was never
documented as an officially supported API.
DEP0064: tls.createSecurePair()#
Type: Runtime
The tls.createSecurePair()
API was deprecated in documentation in Node.js
0.11.3. Users should use tls.Socket
instead.
DEP0065: repl.REPL_MODE_MAGIC and NODE_REPL_MODE=magic#
Type: Documentation-only
The repl
module's REPL_MODE_MAGIC
constant, used for replMode
option, has
been deprecated. Its behavior has been functionally identical to that of
REPL_MODE_SLOPPY
since Node.js v6.0.0, when V8 5.0 was imported. Please use
REPL_MODE_SLOPPY
instead.
The NODE_REPL_MODE
environment variable is used to set the underlying
replMode
of an interactive node
session. Its default value, magic
, is
similarly deprecated in favor of sloppy
.
DEP0066: outgoingMessage._headers, outgoingMessage._headerNames#
Type: Documentation-only
The http
module outgoingMessage._headers
and outgoingMessage._headerNames
properties have been deprecated. Please instead use one of the public methods
(e.g. outgoingMessage.getHeader()
, outgoingMessage.getHeaders()
,
outgoingMessage.getHeaderNames()
, outgoingMessage.hasHeader()
,
outgoingMessage.removeHeader()
, outgoingMessage.setHeader()
) for working
with outgoing headers.
Note: outgoingMessage._headers
and outgoingMessage._headerNames
were
never documented as officially supported properties.
DEP0067: OutgoingMessage.prototype._renderHeaders#
Type: Documentation-only
The http
module OutgoingMessage.prototype._renderHeaders()
API has been
deprecated.
Note: OutgoingMessage.prototype._renderHeaders
was never documented as
an officially supported API.
DEP0068: node debug#
Type: Runtime
node debug
corresponds to the legacy CLI debugger which has been replaced with
a V8-inspector based CLI debugger available through node inspect
.
DEP0069: vm.runInDebugContext(string)#
Type: Documentation-only
The DebugContext will be removed in V8 soon and will not be available in Node 10+.
Note: DebugContext was an experimental API.
DEP0070: async_hooks.currentId()#
Type: Runtime
async_hooks.currentId()
was renamed to async_hooks.executionAsyncId()
for
clarity.
Note: change was made while async_hooks
was an experimental API.
DEP0071: async_hooks.triggerId()#
Type: Runtime
async_hooks.triggerId()
was renamed to async_hooks.triggerAsyncId()
for
clarity.
Note: change was made while async_hooks
was an experimental API.
DEP0072: async_hooks.AsyncResource.triggerId()#
Type: Runtime
async_hooks.AsyncResource.triggerId()
was renamed to
async_hooks.AsyncResource.triggerAsyncId()
for clarity.
Note: change was made while async_hooks
was an experimental API.
DNS#
Stability: 2 - Stable
The dns
module contains functions belonging to two different categories:
1) Functions that use the underlying operating system facilities to perform
name resolution, and that do not necessarily perform any network communication.
This category contains only one function: dns.lookup()
. Developers
looking to perform name resolution in the same way that other applications on
the same operating system behave should use dns.lookup()
.
For example, looking up iana.org
.
const dns = require('dns');
dns.lookup('iana.org', (err, address, family) => {
console.log('address: %j family: IPv%s', address, family);
});
// address: "192.0.43.8" family: IPv4
2) Functions that connect to an actual DNS server to perform name resolution,
and that always use the network to perform DNS queries. This category
contains all functions in the dns
module except dns.lookup()
. These
functions do not use the same set of configuration files used by
dns.lookup()
(e.g. /etc/hosts
). These functions should be used by
developers who do not want to use the underlying operating system's facilities
for name resolution, and instead want to always perform DNS queries.
Below is an example that resolves 'archive.org'
then reverse resolves the IP
addresses that are returned.
const dns = require('dns');
dns.resolve4('archive.org', (err, addresses) => {
if (err) throw err;
console.log(`addresses: ${JSON.stringify(addresses)}`);
addresses.forEach((a) => {
dns.reverse(a, (err, hostnames) => {
if (err) {
throw err;
}
console.log(`reverse for ${a}: ${JSON.stringify(hostnames)}`);
});
});
});
There are subtle consequences in choosing one over the other, please consult the Implementation considerations section for more information.
dns.getServers()#
Returns an array of IP address strings, formatted according to rfc5952, that are currently configured for DNS resolution. A string will include a port section if a custom port is used.
For example:
[
'4.4.4.4',
'2001:4860:4860::8888',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053'
]
dns.lookup(hostname[, options], callback)#
hostname
<string>options
<integer> | <Object>family
<integer> The record family. Must be4
or6
. IPv4 and IPv6 addresses are both returned by default.hints
<number> One or more supportedgetaddrinfo
flags. Multiple flags may be passed by bitwiseOR
ing their values.all
<boolean> Whentrue
, the callback returns all resolved addresses in an array. Otherwise, returns a single address. Defaults tofalse
.
callback
<Function>
Resolves a hostname (e.g. 'nodejs.org'
) into the first found A (IPv4) or
AAAA (IPv6) record. All option
properties are optional. If options
is an
integer, then it must be 4
or 6
– if options
is not provided, then IPv4
and IPv6 addresses are both returned if found.
With the all
option set to true
, the arguments for callback
change to
(err, addresses)
, with addresses
being an array of objects with the
properties address
and family
.
On error, err
is an Error
object, where err.code
is the error code.
Keep in mind that err.code
will be set to 'ENOENT'
not only when
the hostname does not exist but also when the lookup fails in other ways
such as no available file descriptors.
dns.lookup()
does not necessarily have anything to do with the DNS protocol.
The implementation uses an operating system facility that can associate names
with addresses, and vice versa. This implementation can have subtle but
important consequences on the behavior of any Node.js program. Please take some
time to consult the Implementation considerations section before using
dns.lookup()
.
Example usage:
const dns = require('dns');
const options = {
family: 6,
hints: dns.ADDRCONFIG | dns.V4MAPPED,
};
dns.lookup('example.com', options, (err, address, family) =>
console.log('address: %j family: IPv%s', address, family));
// address: "2606:2800:220:1:248:1893:25c8:1946" family: IPv6
// When options.all is true, the result will be an Array.
options.all = true;
dns.lookup('example.com', options, (err, addresses) =>
console.log('addresses: %j', addresses));
// addresses: [{"address":"2606:2800:220:1:248:1893:25c8:1946","family":6}]
If this method is invoked as its util.promisify()
ed version, and all
is not set to true
, it returns a Promise for an object with address
and
family
properties.
Supported getaddrinfo flags#
The following flags can be passed as hints to dns.lookup()
.
dns.ADDRCONFIG
: Returned address types are determined by the types of addresses supported by the current system. For example, IPv4 addresses are only returned if the current system has at least one IPv4 address configured. Loopback addresses are not considered.dns.V4MAPPED
: If the IPv6 family was specified, but no IPv6 addresses were found, then return IPv4 mapped IPv6 addresses. Note that it is not supported on some operating systems (e.g FreeBSD 10.1).
dns.lookupService(address, port, callback)#
address
<string>port
<number>callback
<Function>
Resolves the given address
and port
into a hostname and service using
the operating system's underlying getnameinfo
implementation.
If address
is not a valid IP address, a TypeError
will be thrown.
The port
will be coerced to a number. If it is not a legal port, a TypeError
will be thrown.
On an error, err
is an Error
object, where err.code
is the error code.
const dns = require('dns');
dns.lookupService('127.0.0.1', 22, (err, hostname, service) => {
console.log(hostname, service);
// Prints: localhost ssh
});
If this method is invoked as its util.promisify()
ed version, it returns a
Promise for an object with hostname
and service
properties.
dns.resolve(hostname[, rrtype], callback)#
hostname
<string> Hostname to resolve.rrtype
<string> Resource record type. Default:'A'
.callback
<Function>err
<Error>records
<string[]> | <Object[]> | <string[][]> | <Object>
Uses the DNS protocol to resolve a hostname (e.g. 'nodejs.org'
) into an array
of the resource records. The callback
function has arguments
(err, records)
. When successful, records
will be an array of resource
records. The type and structure of individual results varies based on rrtype
:
rrtype |
records contains |
Result type | Shorthand method |
---|---|---|---|
'A' |
IPv4 addresses (default) | <string> | dns.resolve4() |
'AAAA' |
IPv6 addresses | <string> | dns.resolve6() |
'CNAME' |
canonical name records | <string> | dns.resolveCname() |
'MX' |
mail exchange records | <Object> | dns.resolveMx() |
'NAPTR' |
name authority pointer records | <Object> | dns.resolveNaptr() |
'NS' |
name server records | <string> | dns.resolveNs() |
'PTR' |
pointer records | <string> | dns.resolvePtr() |
'SOA' |
start of authority records | <Object> | dns.resolveSoa() |
'SRV' |
service records | <Object> | dns.resolveSrv() |
'TXT' |
text records | <string> | dns.resolveTxt() |
'ANY' |
any records | <Object> | dns.resolveAny() |
On error, err
is an Error
object, where err.code
is one of the
DNS error codes.
dns.resolve4(hostname[, options], callback)#
hostname
<string> Hostname to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. Whentrue
, the callback receives an array of{ address: '1.2.3.4', ttl: 60 }
objects rather than an array of strings, with the TTL expressed in seconds.
callback
<Function>err
<Error>addresses
<string[]> | <Object[]>
Uses the DNS protocol to resolve a IPv4 addresses (A
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv4 addresses (e.g.
['74.125.79.104', '74.125.79.105', '74.125.79.106']
).
dns.resolve6(hostname[, options], callback)#
hostname
<string> Hostname to resolve.options
<Object>ttl
<boolean> Retrieve the Time-To-Live value (TTL) of each record. Whentrue
, the callback receives an array of{ address: '0:1:2:3:4:5:6:7', ttl: 60 }
objects rather than an array of strings, with the TTL expressed in seconds.
callback
<Function>err
<Error>addresses
<string[]> | <Object[]>
Uses the DNS protocol to resolve a IPv6 addresses (AAAA
records) for the
hostname
. The addresses
argument passed to the callback
function
will contain an array of IPv6 addresses.
dns.resolveCname(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<string[]>
Uses the DNS protocol to resolve CNAME
records for the hostname
. The
addresses
argument passed to the callback
function
will contain an array of canonical name records available for the hostname
(e.g. ['bar.example.com']
).
dns.resolveMx(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<Object[]>
Uses the DNS protocol to resolve mail exchange records (MX
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of objects containing both a priority
and exchange
property (e.g. [{priority: 10, exchange: 'mx.example.com'}, ...]
).
dns.resolveNaptr(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<Object[]>
Uses the DNS protocol to resolve regular expression based records (NAPTR
records) for the hostname
. The addresses
argument passed to the callback
function will contain an array of objects with the following properties:
flags
service
regexp
replacement
order
preference
For example:
{
flags: 's',
service: 'SIP+D2U',
regexp: '',
replacement: '_sip._udp.example.com',
order: 30,
preference: 100
}
dns.resolveNs(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<string[]>
Uses the DNS protocol to resolve name server records (NS
records) for the
hostname
. The addresses
argument passed to the callback
function will
contain an array of name server records available for hostname
(e.g. ['ns1.example.com', 'ns2.example.com']
).
dns.resolvePtr(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<string[]>
Uses the DNS protocol to resolve pointer records (PTR
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of strings containing the reply records.
dns.resolveSoa(hostname, callback)#
hostname
<string>callback
<Function>
Uses the DNS protocol to resolve a start of authority record (SOA
record) for
the hostname
. The address
argument passed to the callback
function will
be an object with the following properties:
nsname
hostmaster
serial
refresh
retry
expire
minttl
{
nsname: 'ns.example.com',
hostmaster: 'root.example.com',
serial: 2013101809,
refresh: 10000,
retry: 2400,
expire: 604800,
minttl: 3600
}
dns.resolveSrv(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<Object[]>
Uses the DNS protocol to resolve service records (SRV
records) for the
hostname
. The addresses
argument passed to the callback
function will
be an array of objects with the following properties:
priority
weight
port
name
{
priority: 10,
weight: 5,
port: 21223,
name: 'service.example.com'
}
dns.resolveTxt(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>addresses
<string[][]>
Uses the DNS protocol to resolve text queries (TXT
records) for the
hostname
. The addresses
argument passed to the callback
function is
is a two-dimensional array of the text records available for hostname
(e.g.,
[ ['v=spf1 ip4:0.0.0.0 ', '~all' ] ]
). Each sub-array contains TXT chunks of
one record. Depending on the use case, these could be either joined together or
treated separately.
dns.resolveAny(hostname, callback)#
hostname
<string>callback
<Function>err
<Error>ret
<Object[][]>
Uses the DNS protocol to resolve all records (also known as ANY
or *
query).
The ret
argument passed to the callback
function will be an array containing
various types of records. Each object has a property type
that indicates the
type of the current record. And depending on the type
, additional properties
will be present on the object:
Type | Properties |
---|---|
"A" |
address / ttl |
"AAAA" |
address / ttl |
"CNAME" |
value |
"MX" |
Refer to dns.resolveMx() |
"NAPTR" |
Refer to dns.resolveNaptr() |
"NS" |
value |
"PTR" |
value |
"SOA" |
Refer to dns.resolveSoa() |
"SRV" |
Refer to dns.resolveSrv() |
"TXT" |
This type of record contains an array property called entries which refers to dns.resolveTxt() , eg. { entries: ['...'], type: 'TXT' } |
Here is a example of the ret
object passed to the callback:
[ { type: 'A', address: '127.0.0.1', ttl: 299 },
{ type: 'CNAME', value: 'example.com' },
{ type: 'MX', exchange: 'alt4.aspmx.l.example.com', priority: 50 },
{ type: 'NS', value: 'ns1.example.com' },
{ type: 'TXT', entries: [ 'v=spf1 include:_spf.example.com ~all' ] },
{ type: 'SOA',
nsname: 'ns1.example.com',
hostmaster: 'admin.example.com',
serial: 156696742,
refresh: 900,
retry: 900,
expire: 1800,
minttl: 60 } ]
dns.reverse(ip, callback)#
ip
<string>callback
<Function>err
<Error>hostnames
<string[]>
Performs a reverse DNS query that resolves an IPv4 or IPv6 address to an array of hostnames.
On error, err
is an Error
object, where err.code
is
one of the DNS error codes.
dns.setServers(servers)#
servers
<string[]> array of rfc5952 formatted addresses
Sets the IP address and port of servers to be used when performing DNS
resolution. The servers
argument is an array of rfc5952 formatted
addresses. If the port is the IANA default DNS port (53) it can be omitted.
For example:
dns.setServers([
'4.4.4.4',
'[2001:4860:4860::8888]',
'4.4.4.4:1053',
'[2001:4860:4860::8888]:1053'
]);
An error will be thrown if an invalid address is provided.
The dns.setServers()
method must not be called while a DNS query is in
progress.
Error codes#
Each DNS query can return one of the following error codes:
dns.NODATA
: DNS server returned answer with no data.dns.FORMERR
: DNS server claims query was misformatted.dns.SERVFAIL
: DNS server returned general failure.dns.NOTFOUND
: Domain name not found.dns.NOTIMP
: DNS server does not implement requested operation.dns.REFUSED
: DNS server refused query.dns.BADQUERY
: Misformatted DNS query.dns.BADNAME
: Misformatted hostname.dns.BADFAMILY
: Unsupported address family.dns.BADRESP
: Misformatted DNS reply.dns.CONNREFUSED
: Could not contact DNS servers.dns.TIMEOUT
: Timeout while contacting DNS servers.dns.EOF
: End of file.dns.FILE
: Error reading file.dns.NOMEM
: Out of memory.dns.DESTRUCTION
: Channel is being destroyed.dns.BADSTR
: Misformatted string.dns.BADFLAGS
: Illegal flags specified.dns.NONAME
: Given hostname is not numeric.dns.BADHINTS
: Illegal hints flags specified.dns.NOTINITIALIZED
: c-ares library initialization not yet performed.dns.LOADIPHLPAPI
: Error loading iphlpapi.dll.dns.ADDRGETNETWORKPARAMS
: Could not find GetNetworkParams function.dns.CANCELLED
: DNS query cancelled.
Implementation considerations#
Although dns.lookup()
and the various dns.resolve*()/dns.reverse()
functions have the same goal of associating a network name with a network
address (or vice versa), their behavior is quite different. These differences
can have subtle but significant consequences on the behavior of Node.js
programs.
dns.lookup()
#
Under the hood, dns.lookup()
uses the same operating system facilities
as most other programs. For instance, dns.lookup()
will almost always
resolve a given name the same way as the ping
command. On most POSIX-like
operating systems, the behavior of the dns.lookup()
function can be
modified by changing settings in nsswitch.conf(5) and/or resolv.conf(5),
but note that changing these files will change the behavior of all other
programs running on the same operating system.
Though the call to dns.lookup()
will be asynchronous from JavaScript's
perspective, it is implemented as a synchronous call to getaddrinfo(3) that
runs on libuv's threadpool. Because libuv's threadpool has a fixed size, it
means that if for whatever reason the call to getaddrinfo(3) takes a long
time, other operations that could run on libuv's threadpool (such as filesystem
operations) will experience degraded performance. In order to mitigate this
issue, one potential solution is to increase the size of libuv's threadpool by
setting the 'UV_THREADPOOL_SIZE'
environment variable to a value greater than
4
(its current default value). For more information on libuv's threadpool, see
the official libuv documentation.
dns.resolve()
, dns.resolve*()
and dns.reverse()
#
These functions are implemented quite differently than dns.lookup()
. They
do not use getaddrinfo(3) and they always perform a DNS query on the
network. This network communication is always done asynchronously, and does not
use libuv's threadpool.
As a result, these functions cannot have the same negative impact on other
processing that happens on libuv's threadpool that dns.lookup()
can have.
They do not use the same set of configuration files than what dns.lookup()
uses. For instance, they do not use the configuration from /etc/hosts
.
Domain#
Stability: 0 - Deprecated
This module is pending deprecation. Once a replacement API has been finalized, this module will be fully deprecated. Most end users should not have cause to use this module. Users who absolutely must have the functionality that domains provide may rely on it for the time being but should expect to have to migrate to a different solution in the future.
Domains provide a way to handle multiple different IO operations as a
single group. If any of the event emitters or callbacks registered to a
domain emit an 'error'
event, or throw an error, then the domain object
will be notified, rather than losing the context of the error in the
process.on('uncaughtException')
handler, or causing the program to
exit immediately with an error code.
Warning: Don't Ignore Errors!#
Domain error handlers are not a substitute for closing down a process when an error occurs.
By the very nature of how throw
works in JavaScript, there is almost
never any way to safely "pick up where you left off", without leaking
references, or creating some other sort of undefined brittle state.
The safest way to respond to a thrown error is to shut down the process. Of course, in a normal web server, there may be many open connections, and it is not reasonable to abruptly shut those down because an error was triggered by someone else.
The better approach is to send an error response to the request that triggered the error, while letting the others finish in their normal time, and stop listening for new requests in that worker.
In this way, domain
usage goes hand-in-hand with the cluster module,
since the master process can fork a new worker when a worker
encounters an error. For Node.js programs that scale to multiple
machines, the terminating proxy or service registry can take note of
the failure, and react accordingly.
For example, this is not a good idea:
// XXX WARNING! BAD IDEA!
const d = require('domain').create();
d.on('error', (er) => {
// The error won't crash the process, but what it does is worse!
// Though we've prevented abrupt process restarting, we are leaking
// resources like crazy if this ever happens.
// This is no better than process.on('uncaughtException')!
console.log(`error, but oh well ${er.message}`);
});
d.run(() => {
require('http').createServer((req, res) => {
handleRequest(req, res);
}).listen(PORT);
});
By using the context of a domain, and the resilience of separating our program into multiple worker processes, we can react more appropriately, and handle errors with much greater safety.
// Much better!
const cluster = require('cluster');
const PORT = +process.env.PORT || 1337;
if (cluster.isMaster) {
// A more realistic scenario would have more than 2 workers,
// and perhaps not put the master and worker in the same file.
//
// It is also possible to get a bit fancier about logging, and
// implement whatever custom logic is needed to prevent DoS
// attacks and other bad behavior.
//
// See the options in the cluster documentation.
//
// The important thing is that the master does very little,
// increasing our resilience to unexpected errors.
cluster.fork();
cluster.fork();
cluster.on('disconnect', (worker) => {
console.error('disconnect!');
cluster.fork();
});
} else {
// the worker
//
// This is where we put our bugs!
const domain = require('domain');
// See the cluster documentation for more details about using
// worker processes to serve requests. How it works, caveats, etc.
const server = require('http').createServer((req, res) => {
const d = domain.create();
d.on('error', (er) => {
console.error(`error ${er.stack}`);
// Note: We're in dangerous territory!
// By definition, something unexpected occurred,
// which we probably didn't want.
// Anything can happen now! Be very careful!
try {
// make sure we close down within 30 seconds
const killtimer = setTimeout(() => {
process.exit(1);
}, 30000);
// But don't keep the process open just for that!
killtimer.unref();
// stop taking new requests.
server.close();
// Let the master know we're dead. This will trigger a
// 'disconnect' in the cluster master, and then it will fork
// a new worker.
cluster.worker.disconnect();
// try to send an error to the request that triggered the problem
res.statusCode = 500;
res.setHeader('content-type', 'text/plain');
res.end('Oops, there was a problem!\n');
} catch (er2) {
// oh well, not much we can do at this point.
console.error(`Error sending 500! ${er2.stack}`);
}
});
// Because req and res were created before this domain existed,
// we need to explicitly add them.
// See the explanation of implicit vs explicit binding below.
d.add(req);
d.add(res);
// Now run the handler function in the domain.
d.run(() => {
handleRequest(req, res);
});
});
server.listen(PORT);
}
// This part is not important. Just an example routing thing.
// Put fancy application logic here.
function handleRequest(req, res) {
switch (req.url) {
case '/error':
// We do some async stuff, and then...
setTimeout(() => {
// Whoops!
flerb.bark();
}, timeout);
break;
default:
res.end('ok');
}
}
Additions to Error objects#
Any time an Error
object is routed through a domain, a few extra fields
are added to it.
error.domain
The domain that first handled the error.error.domainEmitter
The event emitter that emitted an'error'
event with the error object.error.domainBound
The callback function which was bound to the domain, and passed an error as its first argument.error.domainThrown
A boolean indicating whether the error was thrown, emitted, or passed to a bound callback function.
Implicit Binding#
If domains are in use, then all new EventEmitter objects (including Stream objects, requests, responses, etc.) will be implicitly bound to the active domain at the time of their creation.
Additionally, callbacks passed to lowlevel event loop requests (such as to fs.open, or other callback-taking methods) will automatically be bound to the active domain. If they throw, then the domain will catch the error.
In order to prevent excessive memory usage, Domain objects themselves are not implicitly added as children of the active domain. If they were, then it would be too easy to prevent request and response objects from being properly garbage collected.
To nest Domain objects as children of a parent Domain they must be explicitly added.
Implicit binding routes thrown errors and 'error'
events to the
Domain's 'error'
event, but does not register the EventEmitter on the
Domain, so domain.dispose()
will not shut down the EventEmitter.
Implicit binding only takes care of thrown errors and 'error'
events.
Explicit Binding#
Sometimes, the domain in use is not the one that ought to be used for a specific event emitter. Or, the event emitter could have been created in the context of one domain, but ought to instead be bound to some other domain.
For example, there could be one domain in use for an HTTP server, but perhaps we would like to have a separate domain to use for each request.
That is possible via explicit binding.
For example:
// create a top-level domain for the server
const domain = require('domain');
const http = require('http');
const serverDomain = domain.create();
serverDomain.run(() => {
// server is created in the scope of serverDomain
http.createServer((req, res) => {
// req and res are also created in the scope of serverDomain
// however, we'd prefer to have a separate domain for each request.
// create it first thing, and add req and res to it.
const reqd = domain.create();
reqd.add(req);
reqd.add(res);
reqd.on('error', (er) => {
console.error('Error', er, req.url);
try {
res.writeHead(500);
res.end('Error occurred, sorry.');
} catch (er2) {
console.error('Error sending 500', er2, req.url);
}
});
}).listen(1337);
});
domain.create()#
- Returns: <Domain>
Returns a new Domain object.
Class: Domain#
The Domain class encapsulates the functionality of routing errors and uncaught exceptions to the active Domain object.
Domain is a child class of EventEmitter
. To handle the errors that it
catches, listen to its 'error'
event.
domain.members#
An array of timers and event emitters that have been explicitly added to the domain.
domain.add(emitter)#
emitter
<EventEmitter> | <Timer> emitter or timer to be added to the domain
Explicitly adds an emitter to the domain. If any event handlers called by
the emitter throw an error, or if the emitter emits an 'error'
event, it
will be routed to the domain's 'error'
event, just like with implicit
binding.
This also works with timers that are returned from setInterval()
and
setTimeout()
. If their callback function throws, it will be caught by
the domain 'error' handler.
If the Timer or EventEmitter was already bound to a domain, it is removed from that one, and bound to this one instead.
domain.bind(callback)#
callback
<Function> The callback function- Returns: <Function> The bound function
The returned function will be a wrapper around the supplied callback
function. When the returned function is called, any errors that are
thrown will be routed to the domain's 'error'
event.
Example#
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.bind((er, data) => {
// if this throws, it will also be passed to the domain
return cb(er, data ? JSON.parse(data) : null);
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
domain.dispose()#
Stability: 0 - Deprecated. Please recover from failed IO actions explicitly via error event handlers set on the domain.
Once dispose
has been called, the domain will no longer be used by callbacks
bound into the domain via run
, bind
, or intercept
, and a 'dispose'
event
is emitted.
domain.enter()#
The enter
method is plumbing used by the run
, bind
, and intercept
methods to set the active domain. It sets domain.active
and process.domain
to the domain, and implicitly pushes the domain onto the domain stack managed
by the domain module (see domain.exit()
for details on the domain stack). The
call to enter
delimits the beginning of a chain of asynchronous calls and I/O
operations bound to a domain.
Calling enter
changes only the active domain, and does not alter the domain
itself. enter
and exit
can be called an arbitrary number of times on a
single domain.
If the domain on which enter
is called has been disposed, enter
will return
without setting the domain.
domain.exit()#
The exit
method exits the current domain, popping it off the domain stack.
Any time execution is going to switch to the context of a different chain of
asynchronous calls, it's important to ensure that the current domain is exited.
The call to exit
delimits either the end of or an interruption to the chain
of asynchronous calls and I/O operations bound to a domain.
If there are multiple, nested domains bound to the current execution context,
exit
will exit any domains nested within this domain.
Calling exit
changes only the active domain, and does not alter the domain
itself. enter
and exit
can be called an arbitrary number of times on a
single domain.
If the domain on which exit
is called has been disposed, exit
will return
without exiting the domain.
domain.intercept(callback)#
callback
<Function> The callback function- Returns: <Function> The intercepted function
This method is almost identical to domain.bind(callback)
. However, in
addition to catching thrown errors, it will also intercept Error
objects sent as the first argument to the function.
In this way, the common if (err) return callback(err);
pattern can be replaced
with a single error handler in a single place.
Example#
const d = domain.create();
function readSomeFile(filename, cb) {
fs.readFile(filename, 'utf8', d.intercept((data) => {
// note, the first argument is never passed to the
// callback since it is assumed to be the 'Error' argument
// and thus intercepted by the domain.
// if this throws, it will also be passed to the domain
// so the error-handling logic can be moved to the 'error'
// event on the domain instead of being repeated throughout
// the program.
return cb(null, JSON.parse(data));
}));
}
d.on('error', (er) => {
// an error occurred somewhere.
// if we throw it now, it will crash the program
// with the normal line number and stack message.
});
domain.remove(emitter)#
emitter
<EventEmitter> | <Timer> emitter or timer to be removed from the domain
The opposite of domain.add(emitter)
. Removes domain handling from the
specified emitter.
domain.run(fn[, ...args])#
fn
<Function>...args
<any>
Run the supplied function in the context of the domain, implicitly binding all event emitters, timers, and lowlevel requests that are created in that context. Optionally, arguments can be passed to the function.
This is the most basic way to use a domain.
Example:
const domain = require('domain');
const fs = require('fs');
const d = domain.create();
d.on('error', (er) => {
console.error('Caught error!', er);
});
d.run(() => {
process.nextTick(() => {
setTimeout(() => { // simulating some various async stuff
fs.open('non-existent file', 'r', (er, fd) => {
if (er) throw er;
// proceed...
});
}, 100);
});
});
In this example, the d.on('error')
handler will be triggered, rather
than crashing the program.
Domains and Promises#
As of Node 8.0.0, the handlers of Promises are run inside the domain in
which the call to .then
or .catch
itself was made:
const d1 = domain.create();
const d2 = domain.create();
let p;
d1.run(() => {
p = Promise.resolve(42);
});
d2.run(() => {
p.then((v) => {
// running in d2
});
});
A callback may be bound to a specific domain using domain.bind(callback)
:
const d1 = domain.create();
const d2 = domain.create();
let p;
d1.run(() => {
p = Promise.resolve(42);
});
d2.run(() => {
p.then(p.domain.bind((v) => {
// running in d1
}));
});
Note that domains will not interfere with the error handling mechanisms for
Promises, i.e. no error
event will be emitted for unhandled Promise
rejections.
Errors#
Applications running in Node.js will generally experience four categories of errors:
- Standard JavaScript errors such as:
- <EvalError> : thrown when a call to
eval()
fails. - <SyntaxError> : thrown in response to improper JavaScript language syntax.
- <RangeError> : thrown when a value is not within an expected range
- <ReferenceError> : thrown when using undefined variables
- <TypeError> : thrown when passing arguments of the wrong type
- <URIError> : thrown when a global URI handling function is misused.
- <EvalError> : thrown when a call to
- System errors triggered by underlying operating system constraints such as attempting to open a file that does not exist, attempting to send data over a closed socket, etc;
- And User-specified errors triggered by application code.
- Assertion Errors are a special class of error that can be triggered whenever
Node.js detects an exceptional logic violation that should never occur. These
are raised typically by the
assert
module.
All JavaScript and System errors raised by Node.js inherit from, or are instances of, the standard JavaScript <Error> class and are guaranteed to provide at least the properties available on that class.
Error Propagation and Interception#
Node.js supports several mechanisms for propagating and handling errors that occur while an application is running. How these errors are reported and handled depends entirely on the type of Error and the style of the API that is called.
All JavaScript errors are handled as exceptions that immediately generate
and throw an error using the standard JavaScript throw
mechanism. These
are handled using the try / catch
construct provided by the
JavaScript language.
// Throws with a ReferenceError because z is undefined
try {
const m = 1;
const n = m + z;
} catch (err) {
// Handle the error here.
}
Any use of the JavaScript throw
mechanism will raise an exception that
must be handled using try / catch
or the Node.js process will exit
immediately.
With few exceptions, Synchronous APIs (any blocking method that does not
accept a callback
function, such as fs.readFileSync
), will use throw
to report errors.
Errors that occur within Asynchronous APIs may be reported in multiple ways:
- Most asynchronous methods that accept a
callback
function will accept anError
object passed as the first argument to that function. If that first argument is notnull
and is an instance ofError
, then an error occurred that should be handled.
const fs = require('fs');
fs.readFile('a file that does not exist', (err, data) => {
if (err) {
console.error('There was an error reading the file!', err);
return;
}
// Otherwise handle the data
});
When an asynchronous method is called on an object that is an
EventEmitter
, errors can be routed to that object's'error'
event.const net = require('net'); const connection = net.connect('localhost'); // Adding an 'error' event handler to a stream: connection.on('error', (err) => { // If the connection is reset by the server, or if it can't // connect at all, or on any sort of error encountered by // the connection, the error will be sent here. console.error(err); }); connection.pipe(process.stdout);
A handful of typically asynchronous methods in the Node.js API may still use the
throw
mechanism to raise exceptions that must be handled usingtry / catch
. There is no comprehensive list of such methods; please refer to the documentation of each method to determine the appropriate error handling mechanism required.
The use of the 'error'
event mechanism is most common for stream-based
and event emitter-based APIs, which themselves represent a series of
asynchronous operations over time (as opposed to a single operation that may
pass or fail).
For all EventEmitter
objects, if an 'error'
event handler is not
provided, the error will be thrown, causing the Node.js process to report an
unhandled exception and crash unless either: The domain
module is
used appropriately or a handler has been registered for the
process.on('uncaughtException')
event.
const EventEmitter = require('events');
const ee = new EventEmitter();
setImmediate(() => {
// This will crash the process because no 'error' event
// handler has been added.
ee.emit('error', new Error('This will crash'));
});
Errors generated in this way cannot be intercepted using try / catch
as
they are thrown after the calling code has already exited.
Developers must refer to the documentation for each method to determine exactly how errors raised by those methods are propagated.
Node.js style callbacks#
Most asynchronous methods exposed by the Node.js core API follow an idiomatic
pattern referred to as a "Node.js style callback". With this pattern, a
callback function is passed to the method as an argument. When the operation
either completes or an error is raised, the callback function is called with
the Error object (if any) passed as the first argument. If no error was raised,
the first argument will be passed as null
.
const fs = require('fs');
function nodeStyleCallback(err, data) {
if (err) {
console.error('There was an error', err);
return;
}
console.log(data);
}
fs.readFile('/some/file/that/does-not-exist', nodeStyleCallback);
fs.readFile('/some/file/that/does-exist', nodeStyleCallback);
The JavaScript try / catch
mechanism cannot be used to intercept errors
generated by asynchronous APIs. A common mistake for beginners is to try to
use throw
inside a Node.js style callback:
// THIS WILL NOT WORK:
const fs = require('fs');
try {
fs.readFile('/some/file/that/does-not-exist', (err, data) => {
// mistaken assumption: throwing here...
if (err) {
throw err;
}
});
} catch (err) {
// This will not catch the throw!
console.error(err);
}
This will not work because the callback function passed to fs.readFile()
is
called asynchronously. By the time the callback has been called, the
surrounding code (including the try { } catch (err) { }
block will have
already exited. Throwing an error inside the callback can crash the Node.js
process in most cases. If domains are enabled, or a handler has been
registered with process.on('uncaughtException')
, such errors can be
intercepted.
Class: Error#
A generic JavaScript Error
object that does not denote any specific
circumstance of why the error occurred. Error
objects capture a "stack trace"
detailing the point in the code at which the Error
was instantiated, and may
provide a text description of the error.
All errors generated by Node.js, including all System and JavaScript errors,
will either be instances of, or inherit from, the Error
class.
new Error(message)#
message
<string>
Creates a new Error
object and sets the error.message
property to the
provided text message. If an object is passed as message
, the text message
is generated by calling message.toString()
. The error.stack
property will
represent the point in the code at which new Error()
was called. Stack traces
are dependent on V8's stack trace API. Stack traces extend only to either
(a) the beginning of synchronous code execution, or (b) the number of frames
given by the property Error.stackTraceLimit
, whichever is smaller.
Error.captureStackTrace(targetObject[, constructorOpt])#
targetObject
<Object>constructorOpt
<Function>
Creates a .stack
property on targetObject
, which when accessed returns
a string representing the location in the code at which
Error.captureStackTrace()
was called.
const myObject = {};
Error.captureStackTrace(myObject);
myObject.stack; // similar to `new Error().stack`
The first line of the trace will be prefixed with ${myObject.name}: ${myObject.message}
.
The optional constructorOpt
argument accepts a function. If given, all frames
above constructorOpt
, including constructorOpt
, will be omitted from the
generated stack trace.
The constructorOpt
argument is useful for hiding implementation
details of error generation from an end user. For instance:
function MyError() {
Error.captureStackTrace(this, MyError);
}
// Without passing MyError to captureStackTrace, the MyError
// frame would show up in the .stack property. By passing
// the constructor, we omit that frame, and retain all frames below it.
new MyError().stack;
Error.stackTraceLimit#
The Error.stackTraceLimit
property specifies the number of stack frames
collected by a stack trace (whether generated by new Error().stack
or
Error.captureStackTrace(obj)
).
The default value is 10
but may be set to any valid JavaScript number. Changes
will affect any stack trace captured after the value has been changed.
If set to a non-number value, or set to a negative number, stack traces will not capture any frames.
error.code#
The error.code
property is a string label that identifies the kind of error.
See Node.js Error Codes for details about specific codes.
error.message#
The error.message
property is the string description of the error as set by
calling new Error(message)
. The message
passed to the constructor will also
appear in the first line of the stack trace of the Error
, however changing
this property after the Error
object is created may not change the first
line of the stack trace (for example, when error.stack
is read before this
property is changed).
const err = new Error('The message');
console.error(err.message);
// Prints: The message
error.stack#
The error.stack
property is a string describing the point in the code at which
the Error
was instantiated.
For example:
Error: Things keep happening!
at /home/gbusey/file.js:525:2
at Frobnicator.refrobulate (/home/gbusey/business-logic.js:424:21)
at Actor.<anonymous> (/home/gbusey/actors.js:400:8)
at increaseSynergy (/home/gbusey/actors.js:701:6)
The first line is formatted as <error class name>: <error message>
, and
is followed by a series of stack frames (each line beginning with "at ").
Each frame describes a call site within the code that lead to the error being
generated. V8 attempts to display a name for each function (by variable name,
function name, or object method name), but occasionally it will not be able to
find a suitable name. If V8 cannot determine a name for the function, only
location information will be displayed for that frame. Otherwise, the
determined function name will be displayed with location information appended
in parentheses.
It is important to note that frames are only generated for JavaScript
functions. If, for example, execution synchronously passes through a C++ addon
function called cheetahify
, which itself calls a JavaScript function, the
frame representing the cheetahify
call will not be present in the stack
traces:
const cheetahify = require('./native-binding.node');
function makeFaster() {
// cheetahify *synchronously* calls speedy.
cheetahify(function speedy() {
throw new Error('oh no!');
});
}
makeFaster();
// will throw:
// /home/gbusey/file.js:6
// throw new Error('oh no!');
// ^
// Error: oh no!
// at speedy (/home/gbusey/file.js:6:11)
// at makeFaster (/home/gbusey/file.js:5:3)
// at Object.<anonymous> (/home/gbusey/file.js:10:1)
// at Module._compile (module.js:456:26)
// at Object.Module._extensions..js (module.js:474:10)
// at Module.load (module.js:356:32)
// at Function.Module._load (module.js:312:12)
// at Function.Module.runMain (module.js:497:10)
// at startup (node.js:119:16)
// at node.js:906:3
The location information will be one of:
native
, if the frame represents a call internal to V8 (as in[].forEach
).plain-filename.js:line:column
, if the frame represents a call internal to Node.js./absolute/path/to/file.js:line:column
, if the frame represents a call in a user program, or its dependencies.
The string representing the stack trace is lazily generated when the
error.stack
property is accessed.
The number of frames captured by the stack trace is bounded by the smaller of
Error.stackTraceLimit
or the number of available frames on the current event
loop tick.
System-level errors are generated as augmented Error
instances, which are
detailed here.
Class: RangeError#
A subclass of Error
that indicates that a provided argument was not within the
set or range of acceptable values for a function; whether that is a numeric
range, or outside the set of options for a given function parameter.
For example:
require('net').connect(-1);
// throws "RangeError: "port" option should be >= 0 and < 65536: -1"
Node.js will generate and throw RangeError
instances immediately as a form
of argument validation.
Class: ReferenceError#
A subclass of Error
that indicates that an attempt is being made to access a
variable that is not defined. Such errors commonly indicate typos in code, or
an otherwise broken program.
While client code may generate and propagate these errors, in practice, only V8 will do so.
doesNotExist;
// throws ReferenceError, doesNotExist is not a variable in this program.
Unless an application is dynamically generating and running code,
ReferenceError
instances should always be considered a bug in the code
or its dependencies.
Class: SyntaxError#
A subclass of Error
that indicates that a program is not valid JavaScript.
These errors may only be generated and propagated as a result of code
evaluation. Code evaluation may happen as a result of eval
, Function
,
require
, or vm. These errors are almost always indicative of a broken
program.
try {
require('vm').runInThisContext('binary ! isNotOk');
} catch (err) {
// err will be a SyntaxError
}
SyntaxError
instances are unrecoverable in the context that created them –
they may only be caught by other contexts.
Class: TypeError#
A subclass of Error
that indicates that a provided argument is not an
allowable type. For example, passing a function to a parameter which expects a
string would be considered a TypeError.
require('url').parse(() => { });
// throws TypeError, since it expected a string
Node.js will generate and throw TypeError
instances immediately as a form
of argument validation.
Exceptions vs. Errors#
A JavaScript exception is a value that is thrown as a result of an invalid
operation or as the target of a throw
statement. While it is not required
that these values are instances of Error
or classes which inherit from
Error
, all exceptions thrown by Node.js or the JavaScript runtime will be
instances of Error.
Some exceptions are unrecoverable at the JavaScript layer. Such exceptions
will always cause the Node.js process to crash. Examples include assert()
checks or abort()
calls in the C++ layer.
System Errors#
System errors are generated when exceptions occur within the program's runtime environment. Typically, these are operational errors that occur when an application violates an operating system constraint such as attempting to read a file that does not exist or when the user does not have sufficient permissions.
System errors are typically generated at the syscall level: an exhaustive list
of error codes and their meanings is available by running man 2 intro
or
man 3 errno
on most Unices; or online.
In Node.js, system errors are represented as augmented Error
objects with
added properties.
Class: System Error#
error.code#
The error.code
property is a string representing the error code, which is
typically E
followed by a sequence of capital letters.
error.errno#
The error.errno
property is a number or a string.
The number is a negative value which corresponds to the error code defined
in libuv Error handling
. See uv-errno.h header file
(deps/uv/include/uv-errno.h
in the Node.js source tree) for details. In case
of a string, it is the same as error.code
.
error.syscall#
The error.syscall
property is a string describing the syscall that failed.
error.path#
When present (e.g. in fs
or child_process
), the error.path
property is a
string containing a relevant invalid pathname.
error.address#
When present (e.g. in net
or dgram
), the error.address
property is a
string describing the address to which the connection failed.
error.port#
When present (e.g. in net
or dgram
), the error.port
property is a number
representing the connection's port that is not available.
Common System Errors#
This list is not exhaustive, but enumerates many of the common system errors encountered when writing a Node.js program. An exhaustive list may be found here.
EACCES
(Permission denied): An attempt was made to access a file in a way forbidden by its file access permissions.EADDRINUSE
(Address already in use): An attempt to bind a server (net
,http
, orhttps
) to a local address failed due to another server on the local system already occupying that address.ECONNREFUSED
(Connection refused): No connection could be made because the target machine actively refused it. This usually results from trying to connect to a service that is inactive on the foreign host.ECONNRESET
(Connection reset by peer): A connection was forcibly closed by a peer. This normally results from a loss of the connection on the remote socket due to a timeout or reboot. Commonly encountered via thehttp
andnet
modules.EEXIST
(File exists): An existing file was the target of an operation that required that the target not exist.EISDIR
(Is a directory): An operation expected a file, but the given pathname was a directory.EMFILE
(Too many open files in system): Maximum number of file descriptors allowable on the system has been reached, and requests for another descriptor cannot be fulfilled until at least one has been closed. This is encountered when opening many files at once in parallel, especially on systems (in particular, macOS) where there is a low file descriptor limit for processes. To remedy a low limit, runulimit -n 2048
in the same shell that will run the Node.js process.ENOENT
(No such file or directory): Commonly raised byfs
operations to indicate that a component of the specified pathname does not exist -- no entity (file or directory) could be found by the given path.ENOTDIR
(Not a directory): A component of the given pathname existed, but was not a directory as expected. Commonly raised byfs.readdir
.ENOTEMPTY
(Directory not empty): A directory with entries was the target of an operation that requires an empty directory -- usuallyfs.unlink
.EPERM
(Operation not permitted): An attempt was made to perform an operation that requires elevated privileges.EPIPE
(Broken pipe): A write on a pipe, socket, or FIFO for which there is no process to read the data. Commonly encountered at thenet
andhttp
layers, indicative that the remote side of the stream being written to has been closed.ETIMEDOUT
(Operation timed out): A connect or send request failed because the connected party did not properly respond after a period of time. Usually encountered byhttp
ornet
-- often a sign that asocket.end()
was not properly called.
Node.js Error Codes#
ERR_ARG_NOT_ITERABLE#
Used generically to identify that an iterable argument (i.e. a value that works
with for...of
loops) is required, but not provided to a Node.js API.
ERR_FALSY_VALUE_REJECTION#
Used by the util.callbackify()
API when a callbackified Promise
is rejected
with a falsy value (e.g. null
).
ERR_INVALID_ARG_TYPE#
Used generically to identify that an argument of the wrong type has been passed to a Node.js API.
ERR_INVALID_CALLBACK#
Used generically to identify that a callback function is required and has not been provided to a Node.js API.
ERR_INVALID_FILE_URL_HOST#
Used when a Node.js API that consumes file:
URLs (such as certain functions in
the fs
module) encounters a file URL with an incompatible host. Currently,
this situation can only occur on Unix-like systems, where only localhost
or an
empty host is supported.
ERR_INVALID_FILE_URL_PATH#
Used when a Node.js API that consumes file:
URLs (such as certain
functions in the fs
module) encounters a file URL with an incompatible
path. The exact semantics for determining whether a path can be used is
platform-dependent.
ERR_INVALID_HANDLE_TYPE#
Used when an attempt is made to send an unsupported "handle" over an IPC
communication channel to a child process. See child.send()
and
process.send()
for more information.
ERR_INVALID_OPT_VALUE#
Used generically to identify when an invalid or unexpected value has been passed in an options object.
ERR_INVALID_SYNC_FORK_INPUT#
Used when a Buffer
, Uint8Array
or string
is provided as stdio input to a
synchronous fork. See the documentation for the
child_process
module for more information.
ERR_INVALID_THIS#
Used generically to identify that a Node.js API function is called with an
incompatible this
value.
Example:
const { URLSearchParams } = require('url');
const urlSearchParams = new URLSearchParams('foo=bar&baz=new');
const buf = Buffer.alloc(1);
urlSearchParams.has.call(buf, 'foo');
// Throws a TypeError with code 'ERR_INVALID_THIS'
ERR_INVALID_TUPLE#
Used when an element in the iterable
provided to the WHATWG URLSearchParams
constructor does not
represent a [name, value]
tuple – that is, if an element is not iterable, or
does not consist of exactly two elements.
ERR_INVALID_URL#
Used when an invalid URL is passed to the WHATWG
URL
constructor to be parsed. The thrown error object
typically has an additional property 'input'
that contains the URL that failed
to parse.
ERR_INVALID_URL_SCHEME#
Used generically to signify an attempt to use a URL of an incompatible scheme
(aka protocol) for a specific purpose. It is currently only used in the
WHATWG URL API support in the fs
module (which only accepts URLs with
'file'
scheme), but may be used in other Node.js APIs as well in the future.
ERR_IPC_CHANNEL_CLOSED#
Used when an attempt is made to use an IPC communication channel that has already been closed.
ERR_IPC_DISCONNECTED#
Used when an attempt is made to disconnect an already disconnected IPC
communication channel between two Node.js processes. See the documentation for
the child_process
module for more information.
ERR_IPC_ONE_PIPE#
Used when an attempt is made to create a child Node.js process using more than
one IPC communication channel. See the documentation for the
child_process
module for more information.
ERR_IPC_SYNC_FORK#
Used when an attempt is made to open an IPC communication channel with a
synchronous forked Node.js process. See the documentation for the
child_process
module for more information.
ERR_MISSING_ARGS#
Used when a required argument of a Node.js API is not passed. This is currently
only used in the WHATWG URL API for strict compliance with the specification
(which in some cases may accept func(undefined)
but not func()
). In most
native Node.js APIs, func(undefined)
and func()
are treated identically, and
the ERR_INVALID_ARG_TYPE
error code may be used instead.
ERR_SOCKET_ALREADY_BOUND#
Used when an attempt is made to bind a socket that has already been bound.
ERR_SOCKET_BAD_PORT#
Used when an API function expecting a port > 0 and < 65536 receives an invalid value.
ERR_SOCKET_BAD_TYPE#
Used when an API function expecting a socket type (udp4
or udp6
) receives an
invalid value.
ERR_SOCKET_CANNOT_SEND#
Used when data cannot be sent on a socket.
ERR_SOCKET_DGRAM_NOT_RUNNING#
Used when a call is made and the UDP subsystem is not running.
ERR_STDERR_CLOSE#
Used when an attempt is made to close the process.stderr
stream. By design,
Node.js does not allow stdout
or stderr
Streams to be closed by user code.
ERR_STDOUT_CLOSE#
Used when an attempt is made to close the process.stdout
stream. By design,
Node.js does not allow stdout
or stderr
Streams to be closed by user code.
ERR_UNKNOWN_BUILTIN_MODULE#
Used to identify a specific kind of internal Node.js error that should not typically be triggered by user code. Instances of this error point to an internal bug within the Node.js binary itself.
ERR_UNKNOWN_SIGNAL#
Used when an invalid or unknown process signal is passed to an API expecting a
valid signal (such as child.kill()
).
ERR_UNKNOWN_STDIN_TYPE#
Used when an attempt is made to launch a Node.js process with an unknown stdin
file type. Errors of this kind cannot typically be caused by errors in user
code, although it is not impossible. Occurrences of this error are most likely
an indication of a bug within Node.js itself.
ERR_UNKNOWN_STREAM_TYPE#
Used when an attempt is made to launch a Node.js process with an unknown
stdout
or stderr
file type. Errors of this kind cannot typically be caused
by errors in user code, although it is not impossible. Occurrences of this error
are most likely an indication of a bug within Node.js itself.
Events#
Stability: 2 - Stable
Much of the Node.js core API is built around an idiomatic asynchronous event-driven architecture in which certain kinds of objects (called "emitters") periodically emit named events that cause Function objects ("listeners") to be called.
For instance: a net.Server
object emits an event each time a peer
connects to it; a fs.ReadStream
emits an event when the file is opened;
a stream emits an event whenever data is available to be read.
All objects that emit events are instances of the EventEmitter
class. These
objects expose an eventEmitter.on()
function that allows one or more
functions to be attached to named events emitted by the object. Typically,
event names are camel-cased strings but any valid JavaScript property key
can be used.
When the EventEmitter
object emits an event, all of the functions attached
to that specific event are called synchronously. Any values returned by the
called listeners are ignored and will be discarded.
The following example shows a simple EventEmitter
instance with a single
listener. The eventEmitter.on()
method is used to register listeners, while
the eventEmitter.emit()
method is used to trigger the event.
const EventEmitter = require('events');
class MyEmitter extends EventEmitter {}
const myEmitter = new MyEmitter();
myEmitter.on('event', () => {
console.log('an event occurred!');
});
myEmitter.emit('event');