Worker

Note: This feature is available in Web Workers, except for Service Workers.

The Worker interface of the Web 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 the Worker("path/to/worker/script") constructor.

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

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

EventTarget Worker

Constructors

Worker()

Creates a dedicated web worker that executes the script at the specified URL. This also works for Blob 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 a Worker object receives a message that can't be deserialized.

Example

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

js
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 our Basic dedicated worker example (run dedicated worker).

Specifications

Specification
HTML Standard
# dedicated-workers-and-the-worker-interface

Browser compatibility

Report problems with this compatibility data on GitHub
desktopmobileserver
Chrome
Edge
Firefox
Opera
Safari
Chrome Android
Firefox for Android
Opera Android
Safari on iOS
Samsung Internet
WebView Android
WebView on iOS
Deno
Node.js
Worker
Worker() constructor
Support for ECMAScript modules
Strict MIME type checks for worker scripts
options.name parameter
options.type parameter
error event
message event
messageerror event
postMessage
options.includeUserActivation parameter
Non-standard
terminate
Available in workers

Legend

Tip: you can click/tap on a cell for more information.

Full support
Full support
Partial support
Partial support
No support
No support
Non-standard. Check cross-browser support before using.
See implementation notes.
Has more compatibility info.

Support varies for different types of workers. See each worker type's page for specifics.

Cross-origin worker error behavior

In early versions of the spec, loading a cross-origin worker script threw a SecurityError. Nowadays, an error event is thrown instead.

See also