node:worker_threads

Node.js worker_threads module, resolvable via both ESM import and CommonJS require. Backed by a real host bridge: each Worker runs on its own host thread with its own GraalVM context, realm, and event loop. Messages cross threads by structured clone (guest values never cross realms directly).

javascript

import { Worker, isMainThread, parentPort, workerData } from "node:worker_threads";

if (isMainThread) {
  const w = new Worker("./worker.js", { workerData: { n: 41 } });
  w.on("message", (m) => console.log("got", m));
} else {
  parentPort.postMessage(workerData.n + 1);
}

Implemented surface

Export	Description
`Worker`	Constructor accepting `eval`, `workerData`, `transferList`, and `env` options; instances expose `postMessage`, `terminate`, `ref` / `unref`, and the `online` / `message` / `messageerror` / `error` / `exit` events.
`isMainThread`	`true` on the main thread.
`threadId`	Numeric ID of the current thread.
`parentPort`	The `MessagePort` to the parent (in a worker).
`workerData`	The value passed via the `workerData` option.
`SHARE_ENV`	Sentinel for sharing the parent environment.
`MessageChannel` / `MessagePort` / `BroadcastChannel`	Channel primitives.
`getEnvironmentData` / `setEnvironmentData`	Cross-worker environment data.
`receiveMessageOnPort(port)`	Synchronously drain a queued message.
`markAsUntransferable` / `isMarkedAsUntransferable` / `markAsUncloneable`	Present as no-ops.
`resourceLimits`	The worker's resource-limits object.

Not implemented

The following throw ERR_METHOD_NOT_IMPLEMENTED when called: getHeapSnapshot, postMessageToThread, moveMessagePortToContext, and worker.getHeapSnapshot() / worker.getHeapStatistics().

node:worker_threads

Implemented surface

Not implemented

See also