The SharedWorker interface represents a specific kind of worker that can be accessed from several browsing contexts, such as several windows, iframes or even workers. They implement an interface different than dedicated workers and have a different global scope, SharedWorkerGlobalScope.

Note: If SharedWorker can be accessed from several browsing contexts, all those browsing contexts must share the exact same origin (same protocol, host and port).

Note: In Firefox, shared workers cannot be shared between private (i.e. browsing in a private window) and non-private documents (see bug 1177621.)


Inherits properties from its parent, EventTarget, and implements properties from AbstractWorker.

Is an EventListener that is called whenever an ErrorEvent of type error bubbles through the worker.
SharedWorker.port Read only
Returns a MessagePort object used to communicate and control the shared worker.


Creates a shared web worker that executes the script at the specified URL.


Inherits methods from its parent, EventTarget, and implements properties from AbstractWorker.


In our Basic shared worker example (run shared worker), we have two HTML pages, each of which uses some JavaScript to perform a simple calculation. The different scripts are using the same worker file to perform the calculation — they can both access it, even if their pages are running inside different windows.

The following code snippet shows creation of a SharedWorker object using the SharedWorker() constructor. Both scripts contain this:

var myWorker = new SharedWorker("worker.js");

Both scripts then access the worker through a MessagePort object created using the SharedWorker.port property. If the onmessage event is attached using addEventListener, the port is manually started using its start() method:


When the port is started, both scripts post messages to the worker and handle messages sent from it using port.postMessage() and port.onmessage, respectively:

first.onchange = function() {
    console.log('Message posted to worker');

  second.onchange = function() {
    console.log('Message posted to worker');

  myWorker.port.onmessage = function(e) {
    result1.textContent =;
    console.log('Message received from worker');

Inside the worker we use the SharedWorkerGlobalScope.onconnect handler to connect to the same port discussed above. The ports associated with that worker are accessible in the connect event's ports property — we then use MessagePort start() method to start the port, and the onmessage handler to deal with messages sent from the main threads.

onconnect = function(e) {
    var port = e.ports[0];

    port.addEventListener('message', function(e) {
      var workerResult = 'Result: ' + ([0] *[1]);

    port.start(); // Required when using addEventListener. Otherwise called implicitly by onmessage setter.


Specification Status Comment
WHATWG HTML Living Standard
The definition of 'SharedWorker' in that specification.
Living Standard No change from Web Workers.

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari
Support 4 29.0 (29.0) No support 10.60 5
No support 6.1
Feature Android Chrome for Android Firefox Mobile (Gecko) Firefox OS (Gecko) IE Mobile Opera Mobile Safari Mobile
Support No support No support 33.0 (33.0) 2.1 No support 11.5 5.1
No support 7.1

See also


© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.

API Interface Reference SharedWorker Web Workers Workers