Web/API/MessagePort/postMessage

The postMessage() method of the MessagePort interface sends a message from the port, and optionally, transfers ownership of objects to other browsing contexts.

Note: This feature is available in Web Workers.

Syntax

port.postMessage(message, transferList);

Returns

Void.

Parameters

message: The message you want to send through the channel. This can be of any basic data type. Multiple data items can be sent as an array.
transferList Optional: Transferable objects to be transferred — these objects have their ownership transferred to the receiving browsing context, so are no longer usable by the sending browsing context.

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 window.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 ([[../../../../../../../mdn.github.io/dom-examples/channel-messaging-basic/index|run it live too]]).

Specifications

Specification	Status	Comment
HTML Living StandardThe definition of 'postMessage()' 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
`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

Legend

Full support: Full support
No support: No support