ie ff 兼容的 div失去焦点效果

<script>
var oldobj=null;//获得焦点的div
document.onmousedown=Hanlder;
function Hanlder(e)
{
 e=e?e:window.event;
 var tag=e.srcElement?e.srcElement:e.target;
 if(tag.tagName=="DIV")
 {
  if(oldobj==null)
     oldobj=tag;
  else if(oldobj!=tag)
  { 
    oldobj=tag;
    setTimeout("alert('我失去了输入焦点!')",10);    
  }
 }
 else if(oldobj!=null)
 {

    oldobj=null;//把div焦点对象清除
    setTimeout("alert('我失去了输入焦点!')",10);
 }
}
</script>
<div style="width:100px; height:100px; background-color:#0099FF;">aaa</div>
<input type="text"/>
<div style="width:100px; height:100px; background-color:#0099FF;">bbb</div>