js动态平添classname

js动态添加classname 

?
今天无疑在qq拍拍源码上看到一串这样的代码可以动态添加classname觉得不错就抄了下来

<script type="text/javascript">
window.onload = function () {
 var ulBox = document.getElementById("content");
 var list = ulBox.getElementsByTagName("li");
 for (var i=0; i<list.length; i++) {
  list[i].onmouseover=function() {
   this.className="hover";
  }
  list[i].onmouseout=function() {
   this.className="";
  }
 }
}
</script>

?