https://medium.com/better-programming/my-awesome-react-redux-structure-6044e5007e22

_ShowsReducer.js

export default class ShowsReducer extends BaseReducer {
  initialState = {
    currentShowId: '74',
    show: null,
    episodes: [],
    actors: [],
  };

  [ShowsAction.REQUEST_SHOW_FINISHED](state, action) {
    return {
      ...state,
      show: action.payload,
    }
  }

  [ShowsAction.REQUEST_EPISODES_FINISHED](state, action) {
    return {
      ...state,
      episodes: action.payload,
    }
  }

  [ShowsAction.REQUEST_CAST_FINISHED](state, action) {
    return {
      ...state,
      actors: action.payload,
    }
  }
}

BaseReducer.js

export default class BaseReducer {
  initialState = {};

  reducer = (state = this.initialState, action) => {
    const method = this[action.type];

    if (!method || action.error) {
      return state;
    }

    return method.call(this, state, action);
  };
}