var eventMethod = window.addEventListener ? "addEventListener" : "attachEvent";
var eventer = window[eventMethod];
var messageEvent = eventMethod == "attachEvent" ? "onmessage" : "message";
// Listen for a message from the iframe.
eventer(
    messageEvent,
    function (e) {
        if (e.data.height) {
            document.getElementById("sizetracker").style.height = e.data.height + "px";
        }

        if (e.data.redirectTo) {
            window.location.href = e.data.redirectTo;
        }
    },
    false
);