Global objects

These objects are available in all modules.

The following variables may appear to be global but are not. They exist only in the scope of CommonJS modules:

• __dirname
• __filename
• exports
• module
• require()

The objects listed here are specific to Node.js. There are built-in objects that are part of the JavaScript language itself, which are also globally accessible.

This variable may appear to be global but is not. See __dirname.

This variable may appear to be global but is not. See __filename.

A utility class used to signal cancelation in selected Promise-based APIs. The API is based on the Web API AbortController.

const ac = new AbortController();

ac.signal.addEventListener('abort', () => console.log('Aborted!'),
                           { once: true });

ac.abort();

console.log(ac.signal.aborted);  // Prints true

abort(reason?): void

Triggers the abort signal, causing the abortController.signal to emit the 'abort' event.

class AbortSignal extends EventTarget

The AbortSignal is used to notify observers when the abortController.abort() method is called.

AbortSignal.abort(reason?): AbortSignal

Returns a new already aborted AbortSignal.

AbortSignal.timeout(delay): void

Returns a new AbortSignal which will be aborted in delay milliseconds.

AbortSignal.any(signals): void

Returns a new AbortSignal which will be aborted if any of the provided signals are aborted. Its abortSignal.reason will be set to whichever one of the signals caused it to be aborted.

The 'abort' event is emitted when the abortController.abort() method is called. The callback is invoked with a single object argument with a single type property set to 'abort':

const ac = new AbortController();

// Use either the onabort property...
ac.signal.onabort = () => console.log('aborted!');

// Or the EventTarget API...
ac.signal.addEventListener('abort', (event) => {
  console.log(event.type);  // Prints 'abort'
}, { once: true });

ac.abort();

The AbortController with which the AbortSignal is associated will only ever trigger the 'abort' event once. We recommended that code check that the abortSignal.aborted attribute is false before adding an 'abort' event listener.

Any event listeners attached to the AbortSignal should use the { once: true } option (or, if using the EventEmitter APIs to attach a listener, use the once() method) to ensure that the event listener is removed as soon as the 'abort' event is handled. Failure to do so may result in memory leaks.

True after the AbortController has been aborted.

An optional callback function that may be set by user code to be notified when the abortController.abort() function has been called.

An optional reason specified when the AbortSignal was triggered.

const ac = new AbortController();
ac.abort(new Error('boom!'));
console.log(ac.signal.reason);  // Error: boom!

abortSignal.throwIfAborted(): void

If abortSignal.aborted is true, throws abortSignal.reason.

atob(data): void

Global alias for buffer.atob().

An automated migration is available (source):

npx codemod@latest @nodejs/buffer-atob-btoa

See Blob.

See BroadcastChannel.

btoa(data): void

Global alias for buffer.btoa().

An automated migration is available (source):

npx codemod@latest @nodejs/buffer-atob-btoa

Used to handle binary data. See the buffer section.

A browser-compatible implementation of ByteLengthQueuingStrategy.

clearImmediate(immediateObject): void

clearImmediate is described in the timers section.

clearInterval(intervalObject): void

clearInterval is described in the timers section.

clearTimeout(timeoutObject): void

clearTimeout is described in the timers section.

A browser-compatible implementation of CloseEvent. Disable this API with the --no-experimental-websocket CLI flag.

A browser-compatible implementation of CompressionStream.

Used to print to stdout and stderr. See the console section.

A browser-compatible implementation of CountQueuingStrategy.

A browser-compatible implementation of Crypto. This global is available only if the Node.js binary was compiled with including support for the node:crypto module.

A browser-compatible implementation of the Web Crypto API.

A browser-compatible implementation of CryptoKey. This global is available only if the Node.js binary was compiled with including support for the node:crypto module.

A browser-compatible implementation of CustomEvent.

A browser-compatible implementation of DecompressionStream.

The WHATWG DOMException class.

A browser-compatible implementation of ErrorEvent.

A browser-compatible implementation of the Event class. See EventTarget and Event API for more details.

A browser-compatible implementation of EventSource.

A browser-compatible implementation of the EventTarget class. See EventTarget and Event API for more details.

This variable may appear to be global but is not. See exports.

A browser-compatible implementation of the fetch() function.

const res = await fetch('https://nodejs.org/api/documentation.json');
if (res.ok) {
  const data = await res.json();
  console.log(data);
}

The implementation is based upon undici, an HTTP/1.1 client written from scratch for Node.js. You can figure out which version of undici is bundled in your Node.js process reading the process.versions.undici property.

You can use a custom dispatcher to dispatch requests passing it in fetch's options object. The dispatcher must be compatible with undici's Dispatcher class.

fetch(url, { dispatcher: new MyAgent() });

It is possible to change the global dispatcher in Node.js by installing undici and using the setGlobalDispatcher() method. Calling this method will affect both undici and Node.js.

import { setGlobalDispatcher } from 'undici';
setGlobalDispatcher(new MyAgent());

The following globals are available to use with fetch:

• FormData
• Headers
• Request
• Response

See File.

A browser-compatible implementation of FormData.

In browsers, the top-level scope has traditionally been the global scope. This means that var something will define a new global variable, except within ECMAScript modules. In Node.js, this is different. The top-level scope is not the global scope; var something inside a Node.js module will be local to that module, regardless of whether it is a CommonJS module or an ECMAScript module.

A browser-compatible implementation of Headers.

A browser-compatible implementation of localStorage. Data is stored unencrypted in the file specified by the --localstorage-file CLI flag. The maximum amount of data that can be stored is 10 MB. Any modification of this data outside of the Web Storage API is not supported. localStorage data is not stored per user or per request when used in the context of a server, it is shared across all users and requests.

The MessageChannel class. See MessageChannel for more details.

A browser-compatible implementation of MessageEvent.

The MessagePort class. See MessagePort for more details.

This variable may appear to be global but is not. See module.

A partial implementation of the Navigator API.

A partial implementation of window.navigator.

The navigator.hardwareConcurrency read-only property returns the number of logical processors available to the current Node.js instance.

console.log(`This process is running on ${navigator.hardwareConcurrency} logical processors`);

The navigator.language read-only property returns a string representing the preferred language of the Node.js instance. The language will be determined by the ICU library used by Node.js at runtime based on the default language of the operating system.

The value is representing the language version as defined in RFC 5646.

The fallback value on builds without ICU is 'en-US'.

console.log(`The preferred language of the Node.js instance has the tag '${navigator.language}'`);

The navigator.languages read-only property returns an array of strings representing the preferred languages of the Node.js instance. By default navigator.languages contains only the value of navigator.language, which will be determined by the ICU library used by Node.js at runtime based on the default language of the operating system.

The fallback value on builds without ICU is ['en-US'].

console.log(`The preferred languages are '${navigator.languages}'`);

The navigator.locks read-only property returns a LockManager instance that can be used to coordinate access to resources that may be shared across multiple threads within the same process. This global implementation matches the semantics of the browser LockManager API.

// Request an exclusive lock
await navigator.locks.request('my_resource', async (lock) => {
  // The lock has been acquired.
  console.log(`Lock acquired: ${lock.name}`);
  // Lock is automatically released when the function returns
});

// Request a shared lock
await navigator.locks.request('shared_resource', { mode: 'shared' }, async (lock) => {
  // Multiple shared locks can be held simultaneously
  console.log(`Shared lock acquired: ${lock.name}`);
});

// Request an exclusive lock
navigator.locks.request('my_resource', async (lock) => {
  // The lock has been acquired.
  console.log(`Lock acquired: ${lock.name}`);
  // Lock is automatically released when the function returns
}).then(() => {
  console.log('Lock released');
});

// Request a shared lock
navigator.locks.request('shared_resource', { mode: 'shared' }, async (lock) => {
  // Multiple shared locks can be held simultaneously
  console.log(`Shared lock acquired: ${lock.name}`);
}).then(() => {
  console.log('Shared lock released');
});

See worker_threads.locks for detailed API documentation.

The navigator.platform read-only property returns a string identifying the platform on which the Node.js instance is running.

console.log(`This process is running on ${navigator.platform}`);

The navigator.userAgent read-only property returns user agent consisting of the runtime name and major version number.

console.log(`The user-agent is ${navigator.userAgent}`); // Prints "Node.js/21"

The perf_hooks.performance object.

The PerformanceEntry class. See PerformanceEntry for more details.

The PerformanceMark class. See PerformanceMark for more details.

The PerformanceMeasure class. See PerformanceMeasure for more details.

The PerformanceObserver class. See PerformanceObserver for more details.

The PerformanceObserverEntryList class. See PerformanceObserverEntryList for more details.

The PerformanceResourceTiming class. See PerformanceResourceTiming for more details.

The process object. See the process object section.

queueMicrotask(callback): void

The queueMicrotask() method queues a microtask to invoke callback. If callback throws an exception, the process object 'uncaughtException' event will be emitted.

The microtask queue is managed by V8 and may be used in a similar manner to the process.nextTick() queue, which is managed by Node.js. The process.nextTick() queue is always processed before the microtask queue within each turn of the Node.js event loop.

// Here, `queueMicrotask()` is used to ensure the 'load' event is always
// emitted asynchronously, and therefore consistently. Using
// `process.nextTick()` here would result in the 'load' event always emitting
// before any other promise jobs.

DataHandler.prototype.load = async function load(key) {
  const hit = this._cache.get(key);
  if (hit !== undefined) {
    queueMicrotask(() => {
      this.emit('load', hit);
    });
    return;
  }

  const data = await fetchData(key);
  this._cache.set(key, data);
  this.emit('load', data);
};

The WHATWG QuotaExceededError class. Extends DOMException.

A browser-compatible implementation of ReadableByteStreamController.

A browser-compatible implementation of ReadableStream.

A browser-compatible implementation of ReadableStreamBYOBReader.

A browser-compatible implementation of ReadableStreamBYOBRequest.

A browser-compatible implementation of ReadableStreamDefaultController.

A browser-compatible implementation of ReadableStreamDefaultReader.

A browser-compatible implementation of Request.

require(): void

This variable may appear to be global but is not. See require().

A browser-compatible implementation of Response.

A browser-compatible implementation of sessionStorage. Data is stored in memory, with a storage quota of 10 MB. sessionStorage data persists only within the currently running process, and is not shared between workers.

setImmediate(callback, ...args?): void

setImmediate is described in the timers section.

setInterval(callback, delay, ...args?): void

setInterval is described in the timers section.

setTimeout(callback, delay, ...args?): void

setTimeout is described in the timers section.

A browser-compatible implementation of Storage.

structuredClone(value, options?): void

The WHATWG structuredClone method.

A browser-compatible implementation of SubtleCrypto. This global is available only if the Node.js binary was compiled with including support for the node:crypto module.

The WHATWG TextDecoder class. See the TextDecoder section.

A browser-compatible implementation of TextDecoderStream.

The WHATWG TextEncoder class. See the TextEncoder section.

A browser-compatible implementation of TextEncoderStream.

A browser-compatible implementation of TransformStream.

A browser-compatible implementation of TransformStreamDefaultController.

The WHATWG URL class. See the URL section.

The WHATWG URLPattern class. See the URLPattern section.

The WHATWG URLSearchParams class. See the URLSearchParams section.

The object that acts as the namespace for all W3C WebAssembly related functionality. See the Mozilla Developer Network for usage and compatibility.

A browser-compatible implementation of WebSocket. Disable this API with the --no-experimental-websocket CLI flag.

A mostly browser-compatible implementation of Web Workers of the HTML Standard, implemented on top of node:worker_threads. Threads created with it are given the DedicatedWorkerGlobalScope API (self, name, location, navigator, postMessage(), close(), and importScripts()), in addition to the usual Node.js globals, such as process.

// worker.js
addEventListener('message', (event) => {
  postMessage(`${event.data} from ${name}!`);
});

// main.js
const worker = new Worker('./worker.js', { name: 'greeter' });

worker.addEventListener('message', (event) => {
  console.log(event.data); // Prints: Hello from greeter!
  worker.terminate();
});

worker.postMessage('Hello');

Because their lifetime and sharing model depend on origins and browsing contexts, Node.js does not currently implement SharedWorker.

Worker scripts are read synchronously from the local file system or from memory rather than fetched over the network, which changes which URLs are accepted and how failures are reported:

• new Worker() and importScripts() accept only file:, data:, and blob: URLs. Any other scheme makes new Worker() throw a NotSupportedError and importScripts() throw a NetworkError.
• A script that cannot be read makes importScripts() throw a NetworkError; for new Worker() it fires an error event at the Worker object.
• Redirects, the nosniff check, and HTTP MIME type validation do not apply. MIME types are validated only for data: and blob: URLs. The credentials option is validated for API compatibility but has no effect, since no network request is made.
• On the main thread, relative script URLs are resolved against the current working directory, because there is no document base URL. Within a worker they are resolved against the worker's own URL (as is done in the spec).
• For blob: URLs, the script must be held in memory, so blobs backed by a file, such as those returned by fs.openAsBlob(), cannot be used.

Besides script loading, mentioned above:

• Node.js has no origin model, so same-origin and cross-origin distinctions do not exist and location.origin is 'null' for every supported scheme.
• close() terminates the worker immediately instead of following the specification's "closing flag" algorithm, so code remaining in the current task after close() is not executed.
• The worker global is the normal Node.js global object with DedicatedWorkerGlobalScope inserted into its prototype chain, rather than a fresh global created from the interface. Node.js globals such as process, Buffer, and require() remain available to worker scripts.
• ErrorEvents dispatched at Worker instances include message and error, but filename, lineno, and colno are always '', 0, and 0. An uncaught exception terminates the worker thread, and an unhandled error event is not propagated further: it neither reaches the parent's global scope nor affects the exit code of the process.
• The following WorkerGlobalScope events are never dispatched, although their handler properties exist: languagechange, online, and offline, since these concepts do not exist in Node.js; rejectionhandled and unhandledrejection, since Node.js exposes the equivalent does not implement the PromiseRejectionEvent interface or the per-rejection preventDefault() behavior required by the HTML Standard.

Every Web Worker is backed by a node:worker_threads Worker, so the two APIs share their threading, structured clone, and transfer semantics. Inside a worker, [worker_threads.parentPort][] is the port behind self.postMessage() and the worker's message events, isMainThread is false, and workerData is undefined.

Web Workers, like node:worker_threads workers, keep the event loop alive by default. In Node.js, Web Workers implement the Refable protocol, and can be ref'd and unref'd using process.ref(worker) and process.unref(worker).

As a rule of thumb, use node:worker_threads directly when a program needs workerData, a custom env or execArgv, resource limits, stdio redirection, the 'online' and 'exit' events, or worker.threadId; Worker accepts only the name, type, and credentials options and, per the specification, its terminate() returns undefined, rather than a promise. Threads started through node:worker_threads are ordinary Node.js threads and do not get the worker global scope APIs.

A browser-compatible implementation of WritableStream.

A browser-compatible implementation of WritableStreamDefaultController.

A browser-compatible implementation of WritableStreamDefaultWriter.