Table of contents

- About this documentation
  - Contributing
  - Stability index
  - Stability overview
  - JSON output
  - System calls and man pages

## 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.

### Contributing#

Report errors in this documentation in the issue tracker. See the contributing guide for directions on how to submit pull requests.

### Stability index#

Throughout the documentation are indications of a section's stability. Some APIs 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.

The stability indices are as follows:

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

Stability: 1 - Experimental. The feature is not subject to semantic versioning rules. Non-backward compatible changes or removal may occur in any future release. Use of the feature is not recommended in production environments.

Experimental features are subdivided into stages:

- 1.0 - Early development. Experimental features at this stage are unfinished and subject to substantial change.
- 1.1 - Active development. Experimental features at this stage are nearing minimum viability.
- 1.2 - Release candidate. Experimental features at this stage are hopefully ready to become stable. No further breaking changes are anticipated but may still occur in response to user feedback. We encourage user testing and feedback so that we can know that this feature is ready to be marked as stable.

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

Stability: 3 - Legacy. Although this feature is unlikely to be removed and is still covered by semantic versioning guarantees, it is no longer actively maintained, and other alternatives are available.

Features are marked as legacy rather than being deprecated if their use does no harm, and they are widely relied upon within the npm ecosystem. Bugs found in legacy features are unlikely to be fixed.

Use caution when making use of Experimental features, particularly when authoring libraries. Users may not be aware that experimental features are being used. Bugs or behavior changes may surprise users when Experimental API modifications occur. To avoid surprises, use of an Experimental feature may need a command-line flag. Experimental features may also emit a warning.

### Stability overview#

API | Stability
--- | ---
Assert | (2) Stable
Async hooks | (1) Experimental
Asynchronous context tracking | (2) Stable
Buffer | (2) Stable
Child process | (2) Stable
Cluster | (2) Stable
Console | (2) Stable
Crypto | (2) Stable
Diagnostics Channel | (2) Stable
DNS | (2) Stable
Domain | (0) Deprecated
File system | (2) Stable
HTTP | (2) Stable
HTTP/2 | (2) Stable
HTTPS | (2) Stable
Inspector | (2) Stable
Modules: `node:module` API | (1) .2 - Release candidate
Modules: CommonJS modules | (2) Stable
OS | (2) Stable
Path | (2) Stable
Performance measurement APIs | (2) Stable
Punycode | (0) Deprecated
Query string | (2) Stable
Readline | (2) Stable
REPL | (2) Stable
Single executable applications | (1) Experimental: This feature is being designed and will change.
Stream | (2) Stable
String decoder | (2) Stable
Test runner | (2) Stable
Timers | (2) Stable
TLS (SSL) | (2) Stable
Trace events | (1) Experimental
TTY | (2) Stable
UDP/datagram sockets | (2) Stable
URL | (2) Stable
Util | (2) Stable
VM (executing JavaScript) | (2) Stable
Web Crypto API | (2) Stable
Web Streams API | (1) Experimental.
WebAssembly System Interface (WASI) | (1) Experimental
Worker threads | (2) Stable
Zlib | (2) Stable

### JSON output#

Added in: v0.6.12

Every `.html` document has a corresponding `.json` document. This is for IDEs and other utilities that consume the documentation.

### System calls and man pages#

Node.js functions which wrap a system call will document that. The docs link to the corresponding man pages which describe how the system call works.

Most Unix system calls have Windows analogues. Still, behavior differences may be unavoidable.