function getObj(name){
  if (document.getElementById){
  	this.obj = document.getElementById(name);
	this.style = document.getElementById(name).style;
  }
  else if (document.all){
	this.obj = document.all[name];
	this.style = document.all[name].style;
  }
  else if (document.layers){
   	this.obj = document.layers[name];
   	this.style = document.layers[name];
  }
}

var x,y;
var test1 = document.body.scrollHeight;
var test2 = document.body.offsetHeight
if (test1 > test2){
	y = document.body.scrollHeight;
}
else{
	y = document.body.offsetHeight;
}
var x= new getObj('op');
x.style.height=y;