阻止浏览器冒泡事件，兼容firefox和ie

//得到事件
function getEvent(){
     if(window.event)    {return window.event;}
     func=getEvent.caller;
     while(func!=null){
         var arg0=func.arguments[0];
         if(arg0){
             if((arg0.constructor==Event || arg0.constructor ==MouseEvent
                || arg0.constructor==KeyboardEvent)
                ||(typeof(arg0)=="object" && arg0.preventDefault
                && arg0.stopPropagation)){
                 return arg0;
             }
         }
         func=func.caller;
     }
     return null;
}
//阻止冒泡
function cancelBubble()
{
    var e=getEvent();
    if(window.event){
        //e.returnValue=false;//阻止自身行为
        e.cancelBubble=true;//阻止冒泡
     }else if(e.preventDefault){
        //e.preventDefault();//阻止自身行为
        e.stopPropagation();//阻止冒泡
     }
}