当失去焦点时的函数是什么？

1<div id="div1" style="LEFT: 0px; WIDTH: 100px; POSITION: absolute; TOP: 0px; HEIGHT: 100px">
2<table border="1"><tr><td>mydiv</td></tr></table>
3</div>

 1<script language="javascript">   
 2document.onmousedown=b;   
 3function a(){   
 4document.all("div1").style.visibility="hidden";   
 5}   
 6function b(){   
 7try{   
 8for (var obj=window.event.srcElement;obj.tagName!="DIV";obj=obj.parentElement){   
 9}   
10}   
11catch(e){}   
12try{   
13if (obj.id!="div1"){a();}   
14}   
15catch(e){a();}   
16}   
17</script>