以前还真不知道有这个事件，平时也用不上！摘录如下：
<body class='contactlistbody' onbeforeunload="return ConfirmCloseWebMessenger();" onunload="return OnUnloadWebMessenger();" onresize="OnResizeContactWindow();" >
顺便宣传一下Web MSN Messenger : http://webmessenger.msn.com
MSN Web Messenger lets you talk online and in real-time with friends and family using just a web browser! Use it on any shared computer - at school, at work, at a friend's house or anywhere you can't install the MSN Messenger software.