Nested Frame Resize according to Content size

function IFrameResize(obj)
  {
    var contentHeight;

    contentHeight=obj.contentWindow.document.body.scrollHeight;
    obj.style.height= contentHeight + 'px';
    window.parent.document.getElementById("parentframe").style.height = 
    contentHeight + 'px';
    
    alert(contentHeight);
    alert(window.parent.document.getElementById("parentframe").style.height);
  }

I call that above function in child frame onload event.
Parent frame need to be resized according to child frame content size.
How to achieve it?
Thanks in advance.

P.S
I can see my content when i press middle mouse click and all the way scroll down to bottom. So content is just hidden. Is it scrolling problem or something? 
I think it almost there already.