Destroy object when WEB page leaves_html/css_WEB-ITnose

Destroy the object when the WEB page is left

 window.onbeforeunload=function() {    return "你确定要退出本系统吗？"; }  window.onunload=function(){     if(my&& my.sessionId){        Ext.Ajax.request({          url : './userSession.do?method=logout',          method : 'POST',          params : {             sessionId:  my.sessionId          }        });     } }