While creating messageChannel, it internally creates two ports to send the data and forwarded it to another browsing context.
In this scenario, we are sending the data from one iframe to another iframe. Here we are invoking the data in function and passing the data to DOM.
var loadHandler = function(){ var mc, portMessageHandler; mc = new MessageChannel(); window.parent.postMessage('documentAHasLoaded','http://foo.example',[mc.port2]); portMessageHandler = function(portMsgEvent){ alert( portMsgEvent.data ); } mc.port1.addEventListener('message', portMessageHandler, false); mc.port1.start(); } window.addEventListener('DOMContentLoaded', loadHandler, false);