js刷新与关闭页面的代码

<script> 
window.onbeforeunload=function (){ 
alert("===onbeforeunload==="); 
if(event.clientX>document.body.clientWidth && event.clientY < 0 || event.altKey){ 
     alert("已浏览器"); 
}else{ 
     alert("正在刷新页面"); 
} 
} 
</script>