Youtube in React: parse channel information with VIDEO_DETAILS_SUCCESS action

channels.js

function reduceVideoDetails(responses, prevState) {
  const channelResponse = responses.find(response => response.result.kind === CHANNEL_LIST_RESPONSE);
  let channelEntry = {};
  if (channelResponse && channelResponse.result.items) {
    // we're explicitly asking for a channel with a particular id
    // so the response set must either contain 0 items (if a channel with the specified id does not exist)
    // or at most one item (i.e. the channel we've been asking for)
    const channel = channelResponse.result.items[0];
    channelEntry =  {
      [channel.id]: channel,
    }
  }

  return {
    ...prevState,
    byId: {
      ...prevState.byId,
      ...channelEntry,
    }
  };
}