JS实现带缓动动画的导航栏效果

<!DOCTYPE html>
<html lang="en">
 <head>
  <meta charset="utf-8">
  <style type="text/css">
  ul,li { padding: 0; margin: 0; }
  li { list-style: none; }
   #box{
   height: 48px;
   width: 900px;
   background-color: #459DF5;
   margin: 50px auto;
   position: relative;
   }
   #caution {
   width: 150px;
   height: 48px;
   background-color: #4B92D8;
   position: absolute;
   top: 0;
   left: 0;
   }
 #list {
 position: absolute;
 }
   #list li {
   width: 150px;
   height: 48px;
   float: left;
   color: #fff;
   font: 500 20px/48px "微软雅黑";
   text-align: center;
   cursor: pointer;
   }
  </style>
  <script type="text/javascript">
   window.onload = function(){
   //获取ul ID
   var oUl = document.getElementById("list");
   // 获取span ID
   var caution = document.getElementById("caution");
   //获取ul 所有孩子
   var aLi = oUl.children;
   //定时器管理
   var timer = null;
   //缓动
   var leader = 0;
   var target = 0;
    //停留
    var current = 0;
   for(var i = 0;i<aLi.length;i++){
     //鼠标移动
   aLi[i].onmouseover = function(){
      //关闭定时器
   clearInterval(timer);
      //获取当前的left值
   target = this.offsetLeft;
      //开启定时器
   timer = setInterval(autoCaution,20);   
   }
     //鼠标点击
     aLi[i].onmousedown = function(){
      //清楚所有高亮的文字
      for(var j = 0;j<aLi.length;j++){
       aLi[j].style.color = "#fff"; 
      }
      //当前点击栏变为红色
      this.style.color = "#ccc";
      //提示框
      current = this.offsetLeft;
      caution.style.left = current+"px";      
     }
   }
    //鼠标离开
   oUl.onmouseout = function(){
     //关闭定时器
     clearInterval(timer);
     target = current;
     timer = setInterval(autoCaution,20);
   }
   //缓动动画
   function autoCaution(){   
   leader = leader +(target - leader) /10;
   caution.style.left = leader+"px";
   }
   }
  </script>
 </head>
 <body>
  <div id="box">
  <span id="caution"></span>
  <ul id="list">
  <li>首页</li>
  <li>公司简介</li>
  <li>企业文化</li>
  <li>招贤纳士</li>
  <li>企业论坛</li>
  </ul>
  </div>
 </body>
</html>