Web/API/MessagePort

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.

Methods

Inherits methods from its parent, EventTarget

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close(): Disconnects the port, so it is no longer active.

Event handlers

Inherits event handlers from its parent, EventTarget

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

Events

message: Fired when a MessagePort object receives a message. Also available via the onmessage property.
messageerror: Fired when a MessagePort object receives a message that can't be deserialized. Also available via the onmessageerror property.

Example

In the following example, you can see a new channel being created using the 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 ([[../../../../../../mdn.github.io/dom-examples/channel-messaging-basic/index|run it live too]]).

Specifications

Specification	Status	Comment
HTML Living StandardThe definition of 'Message ports' in that specification.	Living Standard

Browser compatibility

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
`MessagePort`	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 Full support Yes	Opera Android Full support 11	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0
`close`	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	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0
`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
`messageerror` event	Chrome Full support 60	Edge Full support 18	Firefox Full support 57	IE ?	Opera Full support 47	Safari ?	WebView Android Full support 60	Chrome Android Full support 60	Firefox Android Full support 57	Opera Android Full support 47	Safari iOS ?	Samsung Internet Android Full support 8.0
`onmessage`	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	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0
`onmessageerror`	Chrome Full support 60	Edge Full support 18	Firefox Full support 57	IE No support No	Opera Full support 47	Safari ?	WebView Android Full support 60	Chrome Android Full support 60	Firefox Android Full support 57	Opera Android Full support 44	Safari iOS ?	Samsung Internet Android Full support 8.0
`postMessage`	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	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0
`start`	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	Safari iOS Full support 5.1	Samsung Internet Android Full support 1.0
Available in workers	Chrome Full support Yes	Edge Full support 12	Firefox Full support 41	IE Full support Yes	Opera Full support Yes	Safari Full support Yes	WebView Android Full support Yes	Chrome Android Full support Yes	Firefox Android Full support 41	Opera Android Full support Yes	Safari iOS Full support Yes	Samsung Internet Android Full support Yes

Legend

Full support: Full support
No support: No support
Compatibility unknown: Compatibility unknown