DedicatedWorkerGlobalScope.onmessage

The onmessage property of the DedicatedWorkerGlobalScope interface represents an EventHandler to be called when the message event occurs and bubbles through the Worker — i.e. when a message is sent to the worker using the Worker.postMessage method.

Syntax

self.onmessage = function() { ... };

Example

The following code snippet shows creation of a Worker object using the Worker() constructor. Messages are passed to the worker when the value inside the form input first changes. A Worker.onmessage handler is also present, to deal with messages are passed back from the worker.

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

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

myWorker.onmessage = function(e) {
  result.textContent = e.data;
  console.log('Message received from worker');
}

In the worker.js script, a DedicatedWorkerGlobalScope.onmessage handler is used to handle messages from the main script:

onmessage = function(e) {
  console.log('Message received from main script');
  var workerResult = 'Result: ' + (e.data[0] * e.data[1]);
  console.log('Posting message back to main script');
  postMessage(workerResult);
}

Notice how in the main script, onmessage has to be called on myWorker, whereas inside the worker script you just need onmessage because the worker is effectively the global scope (the DedicatedWorkerGlobalScope, in this case).

For a full example, see ourBasic dedicated worker example (run dedicated worker).

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'DedicatedWorkerGlobalScope.onmessage' in that specification.
Living Standard  

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
Basic supportChrome Full support 4Edge ? Firefox Full support 3.5IE Full support 10Opera Full support 10.6Safari Full support 4WebView Android ? Chrome Android Full support YesEdge Mobile ? Firefox Android Full support 4Opera Android Full support 11.5Safari iOS Full support 5.1Samsung Internet Android Full support Yes

Legend

Full support  
Full support
Compatibility unknown  
Compatibility unknown

See also

Document Tags and Contributors

Contributors to this page: sideshowbarker, fscholz, teoli, chrisdavidmills, kscarfone
Last updated by: sideshowbarker,