Use onload property for server side controls- iFrame

I'm trying to use the onload property for an iFrame.

JS:

<script type="text/javascript">
  function iframeLoaded() {
      var iFrameID = document.getElementById('iframe1');
      if(iFrameID) {
            // here you can make the height, I delete it first, then I make it again
            iFrameID.height = "";
            iFrameID.height = iFrameID.contentWindow.document.body.scrollHeight + "px";
      }   
  }
</script> 

ASPX:

<iFrame id="iframe1" runat="server" onload="iframeLoaded()"></iFrame> 

This code works only when the runat="server" is removed. Or else it is not recognizing the iframe id.
I tried also with document.getElementById('<%iframe1.ClientID%>');

I also tried the solution at http://stackoverflow.com/questions/13854573/iframe-error-when-runat-server.
It now gives an error - No overload for method takes 0 arguments. What should be passed?