The MessagePort interface of the Channel Messaging API represents one of the two ports of a MessageChannel, allowing messages to be sent from one port and listening out for them arriving at the other.

Note: This feature is available in Web Workers.


Inherits methods from its parent, EventTarget

Sends a message from the port, and optionally, transfers ownership of objects to other browsing contexts.
Starts the sending of messages queued on the port (only needed when using EventTarget.addEventListener; it is implied when using MessagePort.onmessage.)
Disconnects the port, so it is no longer active.

Event handlers

Inherits event handlers from its parent, EventTarget

An EventListener called when a MessageEvent of type message is fired on the port—that is, when the port receives a message.
An EventListener called when a MessageEvent of type MessageError is fired—that is, when it receives a message that cannot be deserialized.


In the following example, you can see a new channel being created using the MessageChannel.MessageChannel constructor.

When the IFrame has loaded, we register an onmessage handler for MessageChannel.port1 and transfer MessageChannel.port2 to the IFrame using the window.postMessage method along with a message.

When a message is received back from the IFrame, the onMessage function simply outputs the message to a paragraph.

var channel = new MessageChannel();
var output = document.querySelector('.output');
var iframe = document.querySelector('iframe');

// Wait for the iframe to load
iframe.addEventListener("load", onLoad);

function onLoad() {
  // Listen for messages on port1
  channel.port1.onmessage = onMessage;

  // Transfer port2 to the iframe
  iframe.contentWindow.postMessage('Hello from the main page!', '*', [channel.port2]);

// Handle messages received on port1
function onMessage(e) {
  output.innerHTML = e.data;

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


Browser compatibilityUpdate compatibility data on GitHub

Chrome Edge Firefox Internet Explorer Opera Safari
Basic support 4 Yes Yes 10 10.6 5
Available in workers Yes ? 41 Yes Yes Yes
close 4 Yes Yes 10 10.6 5
onmessage 4 Yes Yes 10 10.6 5
onmessageerror 60 ? 57 ? 47 ?
postMessage 4 Yes Yes 10 10.6 5
start 4 Yes Yes 10 10.6 5
Android webview Chrome for Android Edge Mobile Firefox for Android Opera for Android iOS Safari Samsung Internet
Basic support Yes 18 Yes Yes 11.5 5.1 ?
Available in workers Yes Yes ? 41 Yes Yes Yes
close Yes 18 Yes No 11.5 5.1 ?
onmessage Yes 18 Yes No 11.5 5.1 ?
onmessageerror 60 60 ? 57 47 ? ?
postMessage Yes 18 Yes No 11.5 5.1 ?
start Yes 18 Yes No 11.5 5.1 ?

See also

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