code: function (event, ce) {
              var ret, self = this;
              ret = self.fn.call(self.context || ce.currentTarget, event, self.data);
              if (self.once) {
                  //noinspection JSUnresolvedFunction
                  ce.removeObserver(self);
              }
              return ret;
          }
docs: simple run current observer's user-defined function
  @param {KISSY.Event.Object} event
  @param {KISSY.Event.Observable} ce
  @return {*} return value of current observer's user-defined function