MessagePort.onmessage

The onmessage event handler of the MessagePort interface is an EventListener, called whenever an MessageEvent of type message is fired on the port — that is, when the port receives a message.

Note: This feature is available in Web Workers.

Syntax

JavaScript
channel.onmessage = function() { ... };

Example

In the following code block, you can see a new channel being created using the MessageChannel.MessageChannel constructor. When the IFrame has loaded, we pass MessageChannel.port2 to the IFrame using MessagePort.postMessage along with a message. The handleMessage handler then responds to a message being sent back from the IFrame using onmessage, putting it into a paragraph — MessageChannel.port1 is listened to, to check when the message arrives.

JavaScript
var channel = new MessageChannel();
var para = document.querySelector('p');
    
var ifr = document.querySelector('iframe');
var otherWindow = ifr.contentWindow;

ifr.addEventListener("load", iframeLoaded, false);
    
function iframeLoaded() {
  otherWindow.postMessage('Hello from the main page!', '*', [channel.port2]);
}

channel.port1.onmessage = handleMessage;
function handleMessage(e) {
  para.innerHTML = e.data;
}   

For a full working example, see our channel messaging basic demo on Github (run it live too).

Specifications

Specification Status Comment
WHATWG HTML Living Standard
The definition of 'onmessage' in that specification.
Living Standard No difference from HTML5 Web Messaging.
HTML5 Web Messaging
The definition of 'onmessage' in that specification.
Recommendation W3C version of the spec

Browser compatibility

Feature Chrome Firefox (Gecko) Internet Explorer Opera Safari (WebKit)
Basic support 4 Not supported 10.0 10.6 5
Available in workers (Yes) 41 (41) (Yes) (Yes) (Yes)
Feature Android Chrome for Android Firefox Mobile (Gecko) Firefox OS (Gecko) IE Phone Opera Mobile Safari Mobile
Basic support 4.4 4 Not supported Not supported 10.0 11.5 5.1
Available in workers (Yes) (Yes) 41.0 (41) (Yes) (Yes) (Yes) (Yes)

See also

License

© 2016 Mozilla Contributors
Licensed under the Creative Commons Attribution-ShareAlike License v2.5 or later.
https://developer.mozilla.org/en-us/docs/web/api/messageport/onmessage

API Channel messaging MessagePort onmessage Property Reference