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Fires when a message is received from another context (frame, window, worker and similar).

Overview Table

Synchronous No
Bubbles No
Target dom/Window
Cancelable No
Default action
## Examples

For example, if document A contains a reference to the contentWindow of document B, script in document A can send document B a message by calling postMessage as follows:

var o = document.getElementsByTagName('iframe')[0];
o.contentWindow.postMessage('Hello World');

The script in document B can respond to the message by registering the onmessage event handler for incoming messages.

window.attachEvent('onmessage',function(e) {
    if (e.domain == '') {
        if ( == 'Hello World') {
        } else {


For info on channel messaging with Workers, see MessagePort and MessageChannel. The onmessage event is fired when script invokes postMessage on a window object to send the target document a message. The data property of the incoming event is set to the value passed in postMessage. **Security Warning: **For best results, check the origin attribute to ensure that messages are only accepted from domains that you expect. For more information, see Section 7.4.2 of the HTML5 (Working Draft) specification from the World Wide Web Consortium (W3C). To invoke this event, do one of the following:

  • Send a cross-document message with postMessage.
  • Send a message to a Worker with postMessage.

The pEvtObj parameter is required for the following interfaces:

Standards information