如何使用Redux Promise Middleware传递附加元数据？

// 定义一个异步操作的action
const fetchUser = (userId) => ({
  type: 'FETCH_USER',
  payload: fetch(`/api/users/${userId}`).then(response => response.json()),
  meta: { userId } // 附加元数据
});

// 在Redux中使用该action
dispatch(fetchUser(123));

// 在Reducer中处理该action
const reducer = (state = {}, action) => {
  switch (action.type) {
    case 'FETCH_USER_PENDING':
      return {
        ...state,
        loading: true
      };
    case 'FETCH_USER_FULFILLED':
      return {
        ...state,
        loading: false,
        user: action.payload,
        userId: action.meta.userId // 获取附加元数据
      };
    case 'FETCH_USER_REJECTED':
      return {
        ...state,
        loading: false,
        error: action.payload
      };
    default:
      return state;
  }
};