Iframe-Höhe automatisch an Inhalt anpassen

content.php

<script type="text/javascript">
  var giframe;
  var gURL;
  function periodicResize(iframe){
    giframe = iframe;
    setInterval(resizeIframe, 500);
  }
  function resizeIframe() {
    if(giframe.contentWindow.document.body != null && giframe.contentWindow.document.body.scrollHeight > 0){
        if(giframe.contentWindow.document.URL != gURL)
            giframe.height = "780px";
        else
            giframe.height = giframe.contentWindow.document.body.scrollHeight + "px";

        gURL = giframe.contentWindow.document.URL;
    }
  }
</script>
<iframe width="100%" height="780" onload="periodicResize(this)" frameborder="0" scrolling="auto" marginheight="0" marginwidth="0" name="roomres" id="roomIFrame"></iframe>