var myEventMethod = window.addEventListener ? "addEventListener" : "attachEvent"; var myEventListener = window[myEventMethod]; var myEventMessage = myEventMethod == "attachEvent" ? "onmessage" : "message"; myEventListener(myEventMessage, function(e) { switch (e.data.action) { case "setHeight": { document.getElementById('form-iframe').height = (e.data.height) + "px"; break; }} }, false);