old_contents: import Twitter from 'twitter'
  import S3TweetRepository from './lib/s3-tweet-repository'
  import slscrypt from '../node_modules/serverless-crypt/dists/slscrypt'
  
  const tweetRepository = new S3TweetRepository(process.env.TWEET_CACHE_BUCKET_NAME)
  
  const handler = (event, context, callback) => {
    return createTwitterClient(process.env.TWITTER_REST_BASE_URL)
      .then(client => {
        const params = {
          screen_name: 'RealTimeWWII',
          trim_user: true,
          exclude_replies: true,
          include_rts: false,
          count: 200,
          tweet_mode: 'extended'
        }
        return client.get('statuses/user_timeline', params)
      })
      .then(tweets => tweetRepository.saveLatestTweets(tweets))
      .catch(err => callback(err))
  }
  
  const createTwitterClient = async (twitterRestBaseUrl) => {
    return new Twitter({
      consumer_key: await slscrypt.get('twitter_consumer_key'),
      consumer_secret: await slscrypt.get('twitter_consumer_secret'),
      access_token_key: await slscrypt.get('twitter_access_token_key'),
      access_token_secret: await slscrypt.get('twitter_access_token_secret'),
      rest_base: twitterRestBaseUrl
    })
  }
  
  export {handler}
  
new_contents: import Twitter from 'twitter'
  import S3TweetRepository from './lib/s3-tweet-repository'
  import slscrypt from '../node_modules/serverless-crypt/dists/slscrypt'
  
  const tweetRepository = new S3TweetRepository(process.env.TWEET_CACHE_BUCKET_NAME)
  
  const createParams = () => {
    return {
      screen_name: 'RealTimeWWII',
      trim_user: true,
      exclude_replies: true,
      include_rts: false,
      count: 200,
      tweet_mode: 'extended'
    }
  }
  
  const handler = async (event, context, callback) => {
    try {
      const client = await createTwitterClient(process.env.TWITTER_REST_BASE_URL)
      const tweets = await client.get('statuses/user_timeline', createParams())
      await tweetRepository.saveLatestTweets(tweets)
    } catch (err) {
      callback(err)
    }
  }
  
  const createTwitterClient = async (twitterRestBaseUrl) => {
    return new Twitter({
      consumer_key: await slscrypt.get('twitter_consumer_key'),
      consumer_secret: await slscrypt.get('twitter_consumer_secret'),
      access_token_key: await slscrypt.get('twitter_access_token_key'),
      access_token_secret: await slscrypt.get('twitter_access_token_secret'),
      rest_base: twitterRestBaseUrl
    })
  }
  
  export {handler}
  
subject: Convert promise chain to async await.