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 (run it live too).

Specifications

Specification Status Comment
HTML Living Standard
The definition of 'postMessage()' in that specification.
Living Standard  

Browser compatibility

Update compatibility data on GitHub
DesktopMobile
ChromeEdgeFirefoxInternet ExplorerOperaSafariAndroid webviewChrome for AndroidEdge MobileFirefox for AndroidOpera for AndroidiOS SafariSamsung Internet
Basic supportChrome Full support 4Edge Full support YesFirefox Full support YesIE Full support 10Opera Full support 10.6Safari Full support 5WebView Android Full support YesChrome Android Full support 18Edge Mobile Full support YesFirefox Android No support NoOpera Android Full support 11.5Safari iOS Full support 5.1Samsung Internet Android ?

Legend

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

See also

Document Tags and Contributors

Last updated by: fscholz,