Web/API/MessagePort/message event

The message event is fired on a MessagePort object when a message arrives on that channel.

Bubbles	No
Cancelable	No
Interface	MessageEvent
Event handler property	onmessage

Examples

Suppose a script creates a MessageChannel and sends one of the ports to a different browsing context, such as another <iframe>, using code like this:

const channel = new MessageChannel();
const myPort = channel.port1;
const targetFrame = window.top.frames[1];
const targetOrigin = 'https://example.org';

const messageControl = document.querySelector('#message');
const channelMessageButton = document.querySelector('#channel-message');

channelMessageButton.addEventListener('click', () => {
    myPort.postMessage(messageControl.value);
})

targetFrame.postMessage('init', targetOrigin, [channel.port2]);

The target can receive the port and start listening for messages on it using code like this:

window.addEventListener('message', (event) => {
    const myPort = event.ports[0];

    myPort.addEventListener('message', (event) => {
        received.textContent = event.data;
    });

    myPort.start();
});

Note that the listener must call MessagePort.start() before any messages will be delivered to this port. This is only needed when using the addEventListener() method: if the receiver uses onmessage instead, start() is called implicitly:

window.addEventListener('message', (event) => {
    const myPort = event.ports[0];

    myPort.onmessage = (event) => {
        received.textContent = event.data;
    };
});

Specifications

Specification	Status
HTML Living Standard	Living Standard

Browser compatibility

The compatibility table on this page is generated from structured data. If you'd like to contribute to the data, please check out https://github.com/mdn/browser-compat-data and send us a pull request.

Update compatibility data on GitHub

	Desktop						Mobile
	Chrome	Edge	Firefox	Internet Explorer	Opera	Safari	Android webview	Chrome for Android	Firefox for Android	Opera for Android	Safari on iOS	Samsung Internet
message event	Chrome Full support 4	Edge Full support 12	Firefox Full support Yes	IE Full support 10	Opera Full support 10.6	Safari Full support 5	WebView Android Full support Yes	Chrome Android Full support 18	Firefox Android No support No	Opera Android Full support 11.5	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0

Legend

Full support  

Full support

No support  

No support

See also

• Related events: messageerror.
• Using channel messaging

MessagePort: message event by Mozilla Contributors is licensed under CC-BY-SA 2.5.