JavaScript code
function createRequest(){
    var request;
    if(window.XMLHttpRequest){ // For Mozilla, Safari, ...
        request = new XMLHttpRequest();
    } else if(window.ActiveXObject){ // For Internet Explorer
        request = new ActiveXObject("Microsoft.XMLHTTP");
    }
    return request;
}
function window.onunload(){
 var ajax=createRequest();
 var url = "dsession.php";
    ajax.open("GET",url,true);
    ajax.onreadystatechange = function () {
        if (ajax.readyState == 4 && ajax.status==200) {
                kk(ajax.responseText);
        }
    }
    ajax.send(null);
}
function kk(str){
  if(str=='ok'){
  alert("session注销拉！");
}
}




dsession.php
PHP code
$rs=session_destory();
if($rs){
echo "ok";
}else{
echo"no";
}


$update="update tables set state='T' where id='用户ID'";//update一下就可以
$rs=session_destory();
if($rs){
echo "ok";
}else{
echo"no";
}