Youtube in React: get comments for video id selector

comments.js

import {createSelector} from 'reselect';
/* ... */
const getCommentIdsForVideo = (state, videoId) => {
  const comment = state.comments.byVideo[videoId];
  if (comment) {
    return comment.ids;
  }
  return [];
};
export const getCommentsForVideo = createSelector(
  getCommentIdsForVideo,
  state => state.comments.byId,
  (commentIds, allComments) => {
    return commentIds.map(commentId => allComments[commentId]);
  }
);