用js怎样获得一个网页里的所有图片链接？

rt
---------------------------------------------------------------

 1<body onload="a()">
 2<script>   
 3function a()   
 4{   
 5for(i=0;i<document.images.length;i++) alert(document.images[i].src)   
 6}   
 7</script>   
 8\---------------------------------------------------------------   
 9  
10<br/><img border="0" src="http://expert.csdn.net/images/csdn.gif"/>
11<br/><img border="0" src="http://expert.csdn.net/images/csdn.gif"/>
12<br/><img border="0" src="http://expert.csdn.net/images/jspd_wdzx_flgg.gif"/>
13<br/><img border="0" src="http://expert.csdn.net/images/jspd_wdzx_flgg.gif"/>
14<br/><img border="0" src="http://expert.csdn.net/images/csdn.gif"/>
15<script language="javascript">   
16for (var i=0; i<document.images.length; i++)   
17alert(document.images[i].src);   
18</script></body>