sense-reducer-1.js

const usersReducer = (state = {users: {}, fetching: {}, cache: {}}, {type, payload}) => {
  switch (type) {
    case START_FETCHING:
      return {
        ...state,
        fetching: {
          ...state.fetching,
          [payload.userId]: payload.promise,
        },
      };

    case STOP_FETCHING:
      return {
        ...state,
        fetching: {
          ...state.fetching,
          [payload.userId]: null,
        },
      };

    case RECEIVE_USER:
      return {
        ...state,
        cache: {
          ...state.fetching,
          [payload.user.id]: {
            expireTime: Date.now() + 60000,
          },
        },
        users: {
          ...state.users,
          [payload.user.id]: payload.user,
        },
      };
  }

  return state;
};