functional?

const { create, assign } = Object,
      { dispatch, getState } = (function () {
        let state = {
          a: 5
        };
        const reduce = (last, action) => {
          const { type, payload } = action;
          switch (type) {
            case 'INCREMENT_A':
              return assign({ a: last.a + payload }, last);
          }
          return last;
        };
      }
      return {
        dispatch: (action) => {
          state = reduce(state, action);
        },
        getState: () => state
      };
    })();

dispatch({
  type: 'INCREMENT_A',
  payload: 5
});
log(getState().a);