Use @lodash/fp to immutable state change in Redux reducer

after.js

import { flow, set } from 'lodash/fp';

const reducer = (state, action) => {
  case HIDDEN_POST: {
    flow(
      set(`posts.${postId}.isHidden`, true ),
      set(`posts.${postId}.commentsCount`, 0 ),
    )(state);
  }
}

before.js

const reducer = (state, action) => {
  case HIDDEN_POST: {
    if (state.posts[action.payload.postId]) {
      return {
        ...state,
        posts: {
          ...state.posts,
          [action.payload.postId]: {
            ...state.posts[action.payload.postId],
            isHidden: true,
            commentsCount: 0,
          },
        },
      };
    }
  }
}