Firebase Function won't return data?

Question

I'm trying to make a HTTPS Callable function that gets Tweets from a user.

In my app:

const getTweets = firebase.functions().httpsCallable('getTweets');

getTweets({
    username: 'someUsername',
})
.then(res => console.log(res))
.catch(e => console.log(e));

But no data is returned... I get a empty object {data: null}

This is the function:

exports.getTweets = functions.https.onCall(async (data, context) => {
    const Twitter = require('twitter');

    const client = new Twitter({
        consumer_key: functions.config().twitter.api_key,
        consumer_secret: functions.config().twitter.api_secret_key,
        access_token_key: functions.config().twitter.access_token,
        access_token_secret: functions.config().twitter.access_token_secret,
    });

    const params = { screen_name: data.username };

    // ======== I've tried this: ======== 
    return client.get('statuses/user_timeline', params, (error, tweets, response) => {
        if (!error) {
            console.log(tweets);
        }
    });

    // ======== And this: ======== 
    client.get('statuses/user_timeline', params, (error, tweets, response) => {
        if (!error) {
            console.log(tweets);
            return tweets;
        }
    });
});

Answer 1

The could be surrounding the use the callback style client.get. Instead try returning a Promise. Promise is natively available without any additional libraries:

exports.getTweets = functions.https.onCall(async (data, context) => {
  const Twitter = require('twitter');

  const client = new Twitter({
      consumer_key: functions.config().twitter.api_key,
      consumer_secret: functions.config().twitter.api_secret_key,
      access_token_key: functions.config().twitter.access_token,
      access_token_secret: functions.config().twitter.access_token_secret,
  });

  const params = { screen_name: data.username };

  return new Promise((resolve, reject) => {
    client.get('statuses/user_timeline', params, (error, tweets, response) => {
      if (error) {
        // Make sure to reject to avoid leaving it hanging in case of error
        return reject(error);
      }

      return resolve(tweets);
    });
  });
});

Hopefully that helps!