Worker
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.
Not all interfaces and functions are available to scripts inside a
Worker. Workers may use XMLHttpRequest for network communication, but its responseXML and channel attributes are always null. (fetch is also available, with no such restrictions.)Constructors
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.
ServiceWorkerinstances 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
Workerobject receives a message that can't be deserialized. rejectionhandled-
Fires every time a
Promiserejects, regardless of whether or not there is a handler to catch the rejection. unhandledrejection-
Fires when a
Promiserejects with no handler to catch the rejection.
Example
The following code snippet creates a
Worker object using the Worker() 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 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 GitHubChrome | Edge | Firefox | Opera | Safari | Chrome Android | Firefox for Android | Opera Android | Safari on iOS | Samsung Internet | WebView Android | Deno | Node.js | |
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Legend
Tip: you can click/tap on a cell for more information.
Full support
Partial support
No support
See implementation notes.
User must explicitly enable this feature.
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
- Using Web Workers
- Functions and classes available to Web Workers
- Other kind of workers:
SharedWorkerand Service Worker. OffscreenCanvasinterface