各位帮忙看看如何改 _JavaScript

各位帮忙看看怎么改

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">

<html>

 <head>

  <title> New Document </title>

  <meta name="Generator" content="EditPlus">

  <meta name="Author" content="">

  <meta name="Keywords" content="">

  <meta name="Description" content="">

 </head>



 <body>

  <pre>

 

 

  r



  rg

  r

  g

  g

</pre>

 <div style="background:green;width:300px;height:300px;"></div>

<pre>

  rg

  r

  

 

   gf

   

   gf

   g

   fgf

   gf

   g

   f

   g

   g

   f

   g

   fr

  r

  gr

  g

  r

  g

  r

  </pre>

  <script type="text/javascript"src="jquery-1.5.js"></script>

  <script type="text/javascript">

       var i=0;

	 $(window).scroll(function(){

     if($("div").offset().top==$(document).scrollTop()){

		j=$(document).scrollTop();

		if(j>i){

			

				$("div").css("position","fixed");

				$("div").css("top",0);

			}

				 i=j;

		}else{

				 j=$(document).scrollTop();

		         i=j;

		         $("div").css("position","static");

			}

	 });

  </script>

 </body>

</html>

我想使滚动条向下移动时，当可视区上边与div接触时，div随着一起下移。滚动条上移时，div也随着一起移动，但在原来的区域落下来。一轮过后div位置没变.谢谢各位了

------解决方案--------------------
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
<title>无标题文档</title>
<script type="text/javascript">
function getTop(dom){
var top=0;
if(document.defaultView&&document.defaultView.getComputedStyle){
top=document.defaultView.getComputedStyle(dom).top;
}else{
top=dom.currentStyle.top;
}
top=top=='auto'?dom.offsetTop:top;
return top;
}
window.onload=function(){
var div=document.getElementsByTagName("div")[0];
var top=getTop(div);
window.onscroll=function(){
var db=document.body;
var de=document.documentElement
------解决方案--------------------
db;
var sctop=de.scrollTop>db.scrollTop?de.scrollTop:db.scrollTop;
if(sctop>=parseInt(top)){
div.style.position='fixed';
div.style.top='0px';
}else{
div.style.position='static';
div.style.top=top;
}
}
}
</script>
</head>

<body>
<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01 Transitional//EN" "http://www.w3.org/TR/html4/loose.dtd">
<html>
<head>
  <title> New Document </title>
  <meta name="Generator" content="EditPlus">
  <meta name="Author" content="">
  <meta name="Keywords" content="">
  <meta name="Description" content="">
</head>

<body>
  <pre>


  r

  rg
  r
  g
  g
  div位置
</pre>
<div style="background:green;width:300px;height:300px;"></div>
<pre>
  rg
  r


   gf

   gf
   g
   fgf
   gf
   g
   f
   g
   g
   f

各位帮忙看看 如何改

各位帮忙看看如何改