关于js循环绑定问题

  <ul id="ul">
        <li>1111</li>
        <li>2222</li>
        <li>3333</li>
        <li>4444</li>
        <li>5555</li>
  </ul>

<script type="text/javascript">
   var oUl = document.getElementById("ul");
   var aLi = oUl.getElementsByTagName("li");
   for(var i = 0; i < aLi.length; i++){  
          aLi[i].onclick = function (){  
             alert(i);  
          };
      }  
</script>