兼容各个浏览器版本的事件监听器工具

var EventUtil = new Object; 
EventUtil.addEvent = function (oTarget, sEventType, fnHandler) { 
  if (oTarget.addEventListener) { 
  oTarget.addEventListener(sEventType, fnHandler, false); 
  } else if (oTarget.attachEvent) { 
  oTarget.attachEvent("on" + sEventType, fnHandler); 
  } else { 
  oTarget["on" + sEventType] = fnHandler; 
  } 
};