Node.js v12.3.0 Documentation

About this Documentation#

Welcome to the official API reference documentation for Node.js!

Node.js is a JavaScript runtime built on the V8 JavaScript engine.


If errors are found in this documentation, please submit an issue or see the contributing guide for directions on how to submit a patch.

Every 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. An HTML template is located at doc/template.html.

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 being redesigned.

The stability indices are as follows:

Stability: 0 - Deprecated. The feature may emit warnings. Backward compatibility is not guaranteed.

Stability: 1 - Experimental. This feature is still under active development and subject to non-backward compatible changes or removal in any future version. Use of the feature is not recommended in production environments. Experimental features are not subject to the Node.js Semantic Versioning model.

Stability: 2 - Stable. Compatibility with the npm ecosystem is a high priority.

Use caution when making use of Experimental features, particularly within modules that are dependencies (or dependencies of dependencies) within a Node.js application. End users may not be aware that experimental features are being used, and may experience unexpected failures or behavior changes when API modifications occur. To help avoid such surprises, Experimental features may require a command-line flag to enable them, or may emit a process warning. By default, such warnings are printed to stderr and may be handled by attaching a listener to the 'warning' event.

JSON Output#

Stability: 1 - Experimental

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.

Syscalls and man pages#

System calls like open(2) and read(2) define the interface between user programs and the underlying operating system. Node.js functions which wrap a syscall, like, will document that. The docs link to the corresponding man pages (short for manual pages) which describe how the syscalls work.

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.js issue 4760.