Js get page height and width compatible with ie firefox chrome etc

 
<script> 
//Get the page height
var yScroll = (document.documentElement.scrollHeight >document.documentElement.clientHeight) ? document.documentElement.scrollHeight : document.documentElement.clientHeight; 
alert(yScroll) 
//Get the page width
var xScroll=(document.documentElement.scrollWidth>document.documentElement.clientWidth) ? document.documentElement.scrollWidth : document.documentElement.scrollWidth; 
alert(xScroll) 
</script>