<!-- Put this before </body> tag -->

<script type="text/javascript">
    function downloadJSAtOnload() {
    var element = document.createElement("script");
    element.src = "defer.js";
    document.body.appendChild(element);
    }
    if (window.addEventListener)
    window.addEventListener("load", downloadJSAtOnload, false);
    else if (window.attachEvent)
    window.attachEvent("onload", downloadJSAtOnload);
    else window.onload = downloadJSAtOnload;
</script>