兼容FF\IE的事件获得方法

function getEvent()
{ 
    if(document.all) return window.event;
    func=getEvent.caller;
    while(func!=null)
    {
         var arg0=func.arguments[0];
         if(arg0)
         {
                    if((arg0.constructor==Event||arg0.constructor ==MouseEvent)||(typeof(arg0)=="object" && arg0.preventDefault && arg0.stopPropagation))
                    {
                         return arg0;
                     }
            }
        func=func.caller;
    }
    return null;
}