title: postMessage Source IFrame
body: <p>I'm working on a website with cross-domain iframes that are resized to the correct height using postMessage. The only problem I'm having is identifying which iframe has which height. The way I've currently got it set up is that when one iframe sends its height to the parent, all the iframes' heights are changed.</p>
  
  <p>Parent:</p>
  
  <pre><code>var eventMethod = window.addEventListener ? "addEventListener" : "attachEvent";
  var eventer = window[eventMethod];
  var messageEvent = eventMethod == "attachEvent" ? "onmessage" : "message";
  
  eventer(messageEvent, function(e) {
      $('iframe').height(e.data);
  }, false);
  </code></pre>
  
  <p>Iframe:</p>
  
  <pre><code>var updateHeight = function() {
      if(window.parent) {
          window.parent.postMessage($('.widget').outerHeight(), '*');
      }
  };
  </code></pre>
  
  <p>Is there some way to identify which iframe sent the <code>message</code> event?</p>