Expand page height to fill the empty space when page height is less than screen height

<script type="text/javascript">
function findAbsolutePosition(obj) {
var curleft = curtop = 0;
if (obj.offsetParent) {
do {
curleft += obj.offsetLeft;
curtop += obj.offsetTop;
} while (obj = obj.offsetParent);
}
return [curleft,curtop];
//returns an array
}
 
var fot = document.getElementById('footer')
var pos = findAbsolutePosition(fot)
 
var thisbot = pos[1] + fot.offsetHeight;
var needheight = thisbot < window.screen.availHeight ? window.screen.availHeight - thisbot : 0
needheight -= fot.offsetHeight;
window.location.hash = needheight
if(needheight)
{
	var nd = document.createElement('div')
	nd.style.height = needheight + 'px'
	nd.style.width = '100%';
	document.getElementById('page').appendChild(nd)
}
</script>

<script type="text/javascript">
 
//window.onload = function () 
{
var thisbot = document.body.offsetHeight
var ph = pageHeight();
var needheight = thisbot < ph  ? ph - thisbot : 0
//needheight-= document.getElementById('footer').offsetHeight;
if(needheight)
{
	var nd = document.createElement('div')
	nd.style.height = needheight + 'px'
	nd.style.width = '100%';
	document.getElementById('page').appendChild(nd)
}
}
 
function pageHeight() {return  window.innerHeight != null? window.innerHeight : document.documentElement && document.documentElement.clientHeight ?  document.documentElement.clientHeight : document.body != null? document.body.clientHeight : null;} 
 
 
</script>