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 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.
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.
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
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| HTML # dedicated-workers-and-the-worker-interface |
Browser compatibility
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Worker
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Worker() constructor
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Support for ECMAScript modules
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Requires
url parameter to be TrustedScriptURL instance when trusted types are enforced
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Strict MIME type checks for worker scripts
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options.name parameter
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options.type parameter
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error event
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message event
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messageerror event
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postMessage
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options.includeUserActivation parameter
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terminate
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Available in workers
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Legend
Tip: you can click/tap on a cell for more information.
- Full support
- Full support
- Partial support
- Partial support
- In development. Supported in a pre-release version.
- In development. Supported in a pre-release version.
- 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
- Using Web Workers
- Functions and classes available to Web Workers
- Other kind of workers:
SharedWorkerand Service Worker. OffscreenCanvasinterface