Youtube update videos reducer with most popular videos by category action

videos.js

import {MOST_POPULAR, MOST_POPULAR_BY_CATEGORY, VIDEO_CATEGORIES} from '../actions/video';
import {SUCCESS} from '../actions';
import {createSelector} from 'reselect';

const initialState = {
  byId: {},
  mostPopular: {},
  categories: {},
};
export default function videos(state = initialState, action) {
  switch (action.type) {
    case MOST_POPULAR[SUCCESS]:
      return reduceFetchMostPopularVideos(action.response, state);
    case VIDEO_CATEGORIES[SUCCESS]:
      return reduceFetchVideoCategories(action.response, state);
    case MOST_POPULAR_BY_CATEGORY[SUCCESS]:
      return reduceFetchMostPopularVideosByCategory(action.response, action.categories, state);
    default:
      return state;
  }
}