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 |
---|---|---|
HTML Living Standard The definition of 'onmessage' in that specification. |
Living Standard |
Browser compatibility
BCD tables only load in the browser