Worker

Baseline Widely available *

This feature is well established and works across many devices and browser versions. It’s been available across browsers since ⁨July 2015⁩.

* Some parts of this feature may have varying levels of support.

Note: This feature is available inWeb Workers, except forService Workers.

TheWorker interface of theWeb Workers API represents a background task that can be created via script, which can send messages back to its creator.

Creating a worker is done by calling theWorker("path/to/worker/script") constructor.

Workers may themselves spawn new workers, as long as those workers are hosted at the sameorigin as the parent page.

Note that not all interfaces and functions are available to web workers. SeeFunctions and classes available to Web Workers for details.

Constructors

Worker(): Creates a dedicated web worker that executes the script at the specified URL. This also works forBlob URLs.

Instance properties

Inherits properties from its parent,EventTarget.

Instance methods

Inherits methods from its parent,EventTarget.

Worker.postMessage(): Sends a message — consisting of any JavaScript object — to the worker's inner scope.
Worker.terminate(): Immediately terminates the worker. This does not let worker finish its operations; it is halted at once.ServiceWorker instances do not support this method.

Events

error: Fires when an error occurs in the worker.
message: Fires when the worker's parent receives a message from that worker.
messageerror: Fires when aWorker object receives a message that can't bedeserialized.

Example

The following code snippet creates aWorker object using theWorker() constructor, then uses the worker object:

const myWorker = new Worker("/worker.js");const first = document.querySelector("input#number1");const second = document.querySelector("input#number2");first.onchange = () => {  myWorker.postMessage([first.value, second.value]);  console.log("Message posted to worker");};

For a full example, see ourBasic dedicated worker example (run dedicated worker).