页面的离开和关闭事件

<script>

var t;

window.onbeforeunload=function(){

setTimeout(function(){t=setTimeout(onunloadcancel,0)},0);

return "确认离开"; 

}

window.onunloadcancel=function(){

clearTimeout(t);//为了防止刷新执行两次

alert("取消离开');

}

</script>