JS判断IE是刷新还是关闭

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){ 
      alert("关闭"); 
              //关闭的代码 
  } 
  else{ 
      alert("刷新"); 
              //刷新的代码 
  } 
}