topics-actions.js

import _ from 'lodash';
import * as types from './actionTypes';
import redditService from '../../services/reddit';

export function fetchTopics() {
  return async(dispatch, getState) => {
    try {
      const subredditArray = await redditService.getDefaultSubreddits();
      const topicsByUrl = _.keyBy(subredditArray, (subreddit) => subreddit.url);
      dispatch({ type: types.TOPICS_FETCHED, topicsByUrl });
    } catch (error) {
      console.error(error);
    }
  };
}

It allows us to use await in the body of the function.