js 离开页面时触发的脚本

function window.onbeforeunload()
  {
   if("<%=isAdvice%>"=="yes")
   {
    var mfaultid=window.document.all("faultIdBox").value;
    var a = window.showModalDialog("adviceConfirm.aspx?faultid="+mfaultid,'','dialogWidth=400px;dialogHeight=190px;center:yes;status:no;help:no') ;
    if(a == 1)
     window.showModalDialog("addAppraise.aspx?faultid="+mfaultid,'','dialogWidth=450px;dialogHeight=360px;center:yes;status:no;help:no') ;
   }
  }