// recieve message
// event object contains:
//  - data: message sent
//  - origin (host from which the message was sent, e.g. http://blah.example.com)
//  - source (reference to a Window object from which message was sent)
function postMessageHandler( event ) {
  console.log("We've got a message!");
  console.log("* Message:", event.data);
  console.log("* Origin:", event.origin);
  console.log("* Source:", event.source);
  
  // check request is from legitimate source and message is expected or not
  if ( event.origin !== 'http://blah.example.com' ) { return; }
  if ( event.data === 'Hello' ) {
    // give response
    event.source.postMessage( 'world!', 'http://blah.example.com' );
    }
}


if (window.addEventListener) {
  window.addEventListener("message", postMessageHandler, false);
  } else {
  window.attachEvent("onmessage", postMessageHandler);
}



// send message to a window object
// postMessage(message, window origin)
//  - message: any object, viz. string, JSON, array, Regex, ImageFile, Blob, etc.
window.postMessage("Hello", "http://blah.example.com");



// Sample Output
/*

We've got a message!
* Message: Hello
* Origin: http://blah.example.com
* Source: 
Window

*/