MessageEvent

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The MessageEvent interface represents a message received by a target object.

This is used to represent messages in:

The action triggered by this event is defined in a function set as the event handler for the relevant message event (e.g. using an onmessage handler as listed above).

Note: This feature is available in Web Workers.

Constructor

MessageEvent()
Creates a new MessageEvent.

Properties

This interface also inherits properties from its parent, Event.

MessageEvent.data Read only
The data sent by the message emitter.
MessageEvent.origin Read only
A USVString representing the origin of the message emitter.
MessageEvent.lastEventId Read only
A DOMString representing a unique ID for the event.
MessageEvent.source Read only
A MessageEventSource (which can be a WindowProxy, MessagePort, or ServiceWorker object) representing the message emitter.
MessageEvent.ports Read only
An array of MessagePort objects representing the ports associated with the channel the message is being sent through (where appropriate, e.g. in channel messaging or when sending a message to a shared worker).

Methods

This interface also inherits methods from its parent, Event.

initMessageEvent()
Initializes a message event. Do not use this anymoreuse the MessageEvent() constructor instead.

Examples

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:

myWorker.port.start();

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

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

myWorker.port.onmessage = function(e) {
  result1.textContent = e.data;
  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: ' + (e.data[0] * e.data[1]);
    port.postMessage(workerResult);
  });

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

Specifications

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

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidFirefox for AndroidOpera for AndroidSafari on iOSSamsung Internet
MessageEventChrome Full support 1Edge Full support YesFirefox Full support 4IE Full support 9Opera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support 3Samsung Internet Android Full support Yes
MessageEventChrome Full support 1Edge Full support YesFirefox Full support 4IE Full support 9Opera ? Safari Full support 10WebView Android Full support 37Chrome Android Full support 18Firefox Android ? Opera Android ? Safari iOS Full support 3Samsung Internet Android ?
dataChrome Full support 1Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support 3Samsung Internet Android Full support Yes
initMessageEvent
Deprecated
Chrome Full support 1Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support 3Samsung Internet Android Full support Yes
lastEventIdChrome Full support 1Edge Full support 17Firefox Full support 4IE Full support 9Opera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support 3Samsung Internet Android Full support Yes
originChrome Full support 1Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support 4Opera Android Full support YesSafari iOS Full support 3Samsung Internet Android Full support Yes
portsChrome Full support 1Edge Full support 12Firefox Full support 4IE Full support 9Opera Full support YesSafari Full support 10WebView Android Full support YesChrome Android Full support YesFirefox Android Full support YesOpera Android Full support YesSafari iOS Full support 3Samsung Internet Android Full support Yes
sourceChrome Full support YesEdge Full support 12Firefox Full support 55IE No support NoOpera Full support YesSafari Full support YesWebView Android Full support YesChrome Android Full support YesFirefox Android Full support 55Opera Android Full support YesSafari iOS Full support YesSamsung Internet Android Full support Yes

Legend

Full support  
Full support
No support  
No support
Compatibility unknown  
Compatibility unknown
Deprecated. Not for use in new websites.
Deprecated. Not for use in new websites.

See also

  • ExtendableMessageEvent — similar to this interface but used in interfaces that needs to give more flexibility to authors.