IE关闭时判断及AJAX注销案例学习

<script language="javascript"> 
window.onbeforeunload = function () { 
var n = window.event.screenX - window.screenLeft; 
var b = n > document.documentElement.scrollWidth - 20; 
if (b && window.event.clientY < 0 || window.event.altKey) { 

try { 
var xmlhttp = new ActiveXObject("Microsoft.XMLHTTP"); 
xmlhttp.open("POST", "LogOut.aspx", false); 
xmlhttp.send(); 
//return true; 
} 
catch (e) { 
alert('delete user account error message:' + e.message); 
} 

//return "你确定要退出系统吗？退出请按'离开此页'"; 
} else { 
//alert("是刷新而非关闭"); 
} 
} 

</script>