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
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.
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 | Edge | Firefox (Gecko) | Internet Explorer | Opera | Safari (WebKit) |
---|---|---|---|---|---|---|
Basic support | 4 | (Yes) | (Yes) | 10.0 | 10.6 | 5 |
Available in workers | (Yes) | ? | 41 (41) | (Yes) | (Yes) | (Yes) |
Feature | Android | Chrome for Android | Edge | Firefox Mobile (Gecko) | Firefox OS (Gecko) | IE Phone | Opera Mobile | Safari Mobile |
---|---|---|---|---|---|---|---|---|
Basic support | 4.4 | 4 | (Yes) | No support | No support | 10.0 | 11.5 | 5.1 |
Available in workers | (Yes) | (Yes) | ? | 41.0 (41) | (Yes) | (Yes) | (Yes) | (Yes) |