JS与CSS实现带碰撞缓冲效果的竖向导航菜单

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<title>碰撞缓冲效果的导航条</title>
<style type="text/css">
* { padding: 0; margin: 0; }
li { list-style: none; }
body { background: #fff; }
ul { width: 202px; margin: 40px auto 0; position: relative; }
li { width: 200px; height: 30px; line-height: 30px; padding-left: 10px; border: 1px solid #ccc; border-left: 3px solid #666; font-size: 14px; color: #333; margin-bottom: 5px; position: relative; z-index: 2; }
a { color: #333; text-decoration: none; }
.active { font-weight: bold; background: #fff0f0; }
#bar { width: 10px; padding-left: 0; background: #cc6699; border: 1px solid #cc6699; position: absolute; top: 0; left: -14px; z-index: 3; }
</style>
<script>
var obj = null;
var aLis = null;
var oBar = null;
var iTime = null;
var iSpeed = 0;
var iAcc = 3;
var onOff = 0;
var iPrev = 0;
var iNext = 0;
function goTime()
{
 for(var i = 0; i < aLis.length; i+=1)
 {
  if(aLis[i] === this)
  {
   var iTarget = (aLis[0].offsetHeight + 5) * i;
   iNext = i;
   onOff = iNext - iPrev;
   if(iTime)
   {
    clearInterval(iTime);
   }
   if(onOff>=0)
   {
    iTime = setInterval("elasticity("+ iTarget +")",35);
   }
   else
   {
    iTime = setInterval("postpone("+ iTarget +")",35);
   }
   iPrev = iNext;
  }
  aLis[i].className="";
  this.className="active";
 }
}
function elasticity(target)
{
 var top = oBar.offsetTop;
 iSpeed+=iAcc;
 top += iSpeed;
 if(top >= target)
 {
  iSpeed*=-0.7;
  if(Math.abs(iSpeed)<=iAcc)
  {
   clearInterval(iTime);
   iTime=null;
  }
  top=target;
 }
 oBar.style.top = top + "px";
}
function postpone(target)
{
 if(oBar.offsetTop===target)
 {
  clearInterval(iTime);
  iTime=null;
 }
 else
 {
  iSpeed = (target - oBar.offsetTop)/4;
  oBar.style.top = oBar.offsetTop + iSpeed + "px";
 }
}
window.onload = function(){
 obj = document.getElementById("nav");
 aLis = obj.getElementsByTagName("li");
 oBar = document.getElementById("bar");
 for(var i = 0; i < aLis.length; i+=1)
 {
  if(aLis[i].id!="bar")
  {
   aLis[i].onmouseover = goTime;
  }
 }
};
</script>
</head>
<body>
<ul id="nav">
 <li class="active"><a href="#">首页</a></li>
 <li><a href="#">本站</a></li>
 <li><a href="#">妙味课程</a></li>
 <li><a href="#">联系方式</a></li>
 <li id="bar">
</ul>
</body>
</html>