如何判断页面是否加载完毕

如何判断页面是否加载完毕？
function on(){
 if ( window.onload )
 {
  alert( "page onload." );
 }
 else{
  window.setTimeout( on, 1000);
 }
}
on();
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寻梦草人的代码
<iframe src="http://www.163.com" id="ice"></iframe>
<script language="javascript">
<!--
var frame = document.getElementById("ice");
frame.onreadystatechange = function(){
 if( this.readyState == "complete" )
  alert('加载完毕!');
}
//-->
</script>
---------------------------------------------------------------

<script>
function loadWindow()
{
   if(frm.document.readyState == "complete") 
       alert("加载完成!");
   else 
       setTimeout("loadWindow()", 500) 
}

loadWindow()
</script>

或者
<script>
timer=setInterval(checkload,100)
function checkload(){
 if(frmid.readyState!="complete")
{ 
   clearInterval(timer);
   alert("加载完毕.")
 }
}

</script>