Web/API/Worker/Worker

The Worker() constructor creates a Worker object that executes the script at the specified URL. This script must obey the same-origin policy.

Note: that there is a disagreement among browser manufacturers about whether a data URI is of the same origin or not. Though Gecko 10.0 (Firefox 10.0 / Thunderbird 10.0 / SeaMonkey 2.7) and later accept data URIs, that's not the case in all other browsers.

Syntax

var myWorker = new Worker(aURL, options);

Parameters

aURL: A USVString representing the URL of the script the worker will execute. It must obey the same-origin policy.
options Optional: An object containing option properties that can be set when creating the object instance. Available properties are as follows:

type

A DOMString specifying the type of worker to create. The value can be classic or module. If not specified, the default used is classic.
credentials: A DOMString specifying the type of credentials to use for the worker. The value can be omit, same-origin, or include. If not specified, or if type is classic, the default used is omit (no credentials required).
name: A DOMString specifying an identifying name for the DedicatedWorkerGlobalScope representing the scope of the worker, which is mainly useful for debugging purposes.

Exceptions

A SecurityError is raised if the document is not allowed to start workers, e.g. if the URL has an invalid syntax or if the same-origin policy is violated.
A NetworkError is raised if the MIME type of the worker script is incorrect. It should always be text/javascript (for historical reasons other JavaScript MIME types may be accepted).
A SyntaxError is raised if aURL cannot be parsed.

Examples

The following code snippet shows creation of a Worker object using the Worker() constructor and subsequent usage of the object:

var myWorker = new Worker('worker.js');

first.onchange = function() {
  myWorker.postMessage([first.value,second.value]);
  console.log('Message posted to worker');
}

For a full example, see our Basic dedicated worker example ([[../../../../../../../mdn.github.io/simple-web-worker/index|run dedicated worker]]).

Specifications

Specification	Status	Comment
HTML Living StandardThe definition of 'Worker()' in that specification.	Living Standard

Browser compatibility

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
`Worker()` constructor	Chrome Full support 4	Edge Full support 12	Firefox Full support 3.5	IE Full support 10	Opera Full support 10.6	Safari Full support 4	WebView Android Full support 4	Chrome Android Full support 18	Firefox Android Full support 4	Opera Android Full support 11	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0
Support for ECMAScript modules	Chrome Full support 80	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support 67	Safari No support No	WebView Android Full support 80	Chrome Android Full support 80	Firefox Android No support No	Opera Android Full support 57	Safari iOS No support No	Samsung Internet Android Full support 13.0
Strict MIME type checks for worker scripts	Chrome ?	Edge ?	Firefox Full support 81	IE No support No	Opera ?	Safari ?	WebView Android ?	Chrome Android ?	Firefox Android Full support 81	Opera Android ?	Safari iOS ?	Samsung Internet Android ?
Constructor `name` option	Chrome Full support 70	Edge Full support 18	Firefox Full support 55	IE No support No	Opera Full support 57	Safari No support No Notes' No support No Notes' Notes' Supported in Safari Technology Preview 64	WebView Android No support No	Chrome Android Full support 70	Firefox Android Full support 55	Opera Android Full support 49	Safari iOS No support No Notes' No support No Notes' Notes' Supported in Safari Technology Preview 64	Samsung Internet Android Full support 10.0
Constructor `type` option	Chrome Full support 80	Edge Full support 80	Firefox No support No	IE No support No	Opera Full support 67	Safari No support No	WebView Android Full support 80	Chrome Android Full support 80	Firefox Android No support No	Opera Android Full support 57	Safari iOS No support No	Samsung Internet Android Full support 13.0

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown
See implementation notes.': See implementation notes.

Note: A browser can be marked as providing full support for Worker() even though it does not support worker scripts written as modules. As of Mar 1, 2019, only Chrome 80+ supports this feature, while Firefox has an open feature request. No other browsers are known to have support for production usage of worker scripts written as modules. Without that support, worker scripts written as modules and modules used by worker scripts have to be transpiled or otherwise converted to non-module code in order to run.