Facebook-Clone/frontend/reducers/posts_reducer.js

import {
  RECEIVE_ALL_POSTS,
  RECEIVE_POST,
  REMOVE_POST,
} from '../actions/post_actions';
import merge from 'lodash/merge';

const PostsReducer = (oldState = {}, action) => {
  Object.freeze(oldState);
  switch (action.type) {
    case RECEIVE_ALL_POSTS:
      return action.posts;
    case RECEIVE_POST:
      return Object.assign({}, oldState,{[action.post.id]: action.post});
    case REMOVE_POST:
      let newState = merge({}, oldState);
      delete newState[action.postId];
      return newState;
    default:
      return oldState;
  }
};

export default PostsReducer;