Script Sense: Javascript > Hacking Auto-Sizing IFRAME tag

<html>
<head>
<script type="text/javascript">

/***********************************************
* IFrame SSI script- © Dynamic Drive DHTML code library (http://www.dynamicdrive.com)
* Visit DynamicDrive.com for hundreds of original DHTML scripts
* This notice must stay intact for legal use
***********************************************/

//Input the IDs of the IFRAMES you wish to dynamically resize to match its content height:
//Separate each ID with a comma. Examples: ["myframe1", "myframe2"] or ["myframe"] or [] for none:
var iframeids=["myframe"]

//Should script hide iframe from browsers that don't support this script (non IE5+/NS6+ browsers. Recommended):
var iframehide="yes"

var getFFVersion=navigator.userAgent.substring(navigator.userAgent.indexOf("Firefox")).split("/")[1]
var FFextraHeight=parseFloat(getFFVersion)>=0.1? 16 : 0 //extra height in px to add to iframe in FireFox 1.0+ browsers

function dyniframesize() {
var dyniframe=new Array()
for (i=0; i<iframeids.length; i++){
if (document.getElementById){ //begin resizing iframe procedure
dyniframe[dyniframe.length] = document.getElementById(iframeids[i]);
if (dyniframe[i] && !window.opera){
dyniframe[i].style.display="block"
if (dyniframe[i].contentDocument && dyniframe[i].contentDocument.body.offsetHeight) //ns6 syntax
dyniframe[i].height = dyniframe[i].contentDocument.body.offsetHeight+FFextraHeight;
else if (dyniframe[i].Document && dyniframe[i].Document.body.scrollHeight) //ie5+ syntax
dyniframe[i].height = dyniframe[i].Document.body.scrollHeight;
}
}
//reveal iframe for lower end browsers? (see var above):
if ((document.all || document.getElementById) && iframehide=="no"){
var tempobj=document.all? document.all[iframeids[i]] : document.getElementById(iframeids[i])
tempobj.style.display="block"
}
}
}

if (window.addEventListener)
window.addEventListener("load", dyniframesize, false)
else if (window.attachEvent)
window.attachEvent("onload", dyniframesize)
else
window.onload=dyniframesize

</script>
</head>

<body>

<iframe id="myframe" src="externalpage.htm" scrolling="no" marginwidth="0" marginheight="0" frameborder="0" vspace="0" hspace="0" style="overflow:visible; width:100%; display:none"></iframe>

</body>
</html>

Source : http://www.dynamicdrive.com/