<div id="tabarea">     <ul class="clearFix">         <li>aaaaaaaaaa</li>         <li>bbbbbbbbbb</li>         <li>cccccccccc</li>         <li>dddddddddd</li>     </ul>      <div class="box active">1</div>     <div class="box">2</div>     <div class="box">3</div>     <div class="box">4</div> </div>  <script> function tab(){     var eleId = document.getElementById("tabarea");     var li = eleId.getElementsByTagName("li");     var div = eleId.getElementsByTagName("div");      for(var i=0;i<li.length;i++){         li[i].onclick = function(){             for(var j=0; j<li.length; j++) {                 if (this == li[j]) {                     li[j].className = "on";                     div[j].className = "box active";                 }                 else {                     li[j].className = "";                     div[j].className = "box";                }             }         }     } }  tab(); </script>

有一处不明白的地方,点击li[i]的时候js怎么给第div[i]添加classname的