JS 监听浏览器封锁和刷新 _JavaScript

JS 监听浏览器关闭和刷新
<script language="JavaScript">
     window.onbeforeunload = onbeforeunload_handler;
     window.onunload = onunload_handler;

     function onbeforeunload_handler(){
    var warning="离开此页面将退出系统！";
         return warning;
     }

     function onunload_handler(){
        /* var warning="谢谢光临";
         alert(warning); */
       　　 Logout();

     }

     var xmlhttp;
     function Logout(){
    xmlhttp=null;
    if (window.XMLHttpRequest)
       {// code for all new browsers
       xmlhttp=new XMLHttpRequest();

       }
    else if (window.ActiveXObject)
       {// code for IE5 and IE6
       xmlhttp=new ActiveXObject("Microsoft.XMLHTTP");
       alert("你的浏览器是旧的！");
       }
    if (xmlhttp!=null)
       {
       xmlhttp.onreadystatechange=state_Change;
       xmlhttp.open("GET","edsqc/logout",false);
       xmlhttp.send(null);
       }
    else
       {
    alert("Your browser does not support XMLHTTP.");
       }
    }

   function state_Change()
    {
    if (xmlhttp.readyState==4)
       {// 4 = "loaded"

       if (xmlhttp.status==200)
         {// 200 = OK
        alert(xmlhttp.responseText);
    /* document.write(xmlhttp.responseText); */

         }
       else
         {
          alert("Problem retrieving XML data !");
         }
       }

    }
    　　


        </script>