获取浏览器当前事件对象

  function getEvent(event) {
          var ev = event || window.event;

          if (!ev) {
          var c = this.getEvent.caller;
          while (c) {
            ev = c.arguments[0];
            if (ev && (Event == ev.constructor || MouseEvent  == ev.constructor)) {
                break;
            }
            c = c.caller;
            }
         }

         return ev;
       }