Adding results from multiple requests - Node JS

Question

I'm trying to use Spotify's API to get a list of all the saved tracks of a certain user (afterwords I need to randomize 10 songs from that list, but I'm not able to get to that point).

I'm a beginner in Node JS and still trying to understand the concepts of callbacks and promises. I'm trying to use axios to make all requests. Here's the code I have so far:

let tracks = []
function getTracks(offset, access) {
    const auth = {
        headers: { Authorization: 'Bearer ' + access }
    }
    return axios.get('https://api.spotify.com/v1/me/tracks?limit=50' + (offset > 0 ? '&offset=' + offset : ''), auth) // url changes based on offset value
        .then(result => {
            result.data.items.forEach(element => {
                tracks.push({ title: element.track.name, artist: element.track.artists });
            });
            return result.data.total;
        })
        .catch(error => {
            return error;
        });
}

router.get('/getsongs', function (req, res) {
    const access_token = req.query.access || null; // contains access token
    getTracks(0, access_token).then(data => {
        const total = (data / 50) + 1;
        for (let i = 1; i <= total; i++) {
            getTracks(i * 50, access_token).then(moredata => {
                // I'm not sure what I can put in here
                // I tried 'console.log('test')' and it does print a certain amount of times based on the loop
            });
        }    
    });
    res.send(tracks);
});

The idea behind this is to make one first request for 50 tracks, and then find the total number of tracks. After that, I'll loop a certain amount of times based off the total, and set an offset each time to get the next 50 tracks. All the tracks are added to a global list tracks, which I send to the client after all the requests are done.

I've tried many different versions of this, and no matter what I either end up with an empty list or only a list of the first 50 tracks.

How can I end up with one list containing all the tracks that I can use later in the program?

Thanks!

Nghia Pham · Accepted Answer · 2019-10-21 04:18:30Z

You can try using Promise.all

router.get('/getsongs', function(req, res) {
  let asyncTasks = [];
  const access_token = req.query.access || null; // contains access token
  return getTracks(0, access_token).then(data => {
      const total = data / 50 + 1;
      for (let i = 1; i <= total; i++) {
        asyncTasks.push(getTracks(i * 50, access_token));
      }
      return Promise.all(asyncTasks);
    })
    .then(listTrack => {
      console.log(listTrack)
    });
});

You are nested Promise here and this's a bad practice which is called Promise hell

getTracks(0, access_token).then(data => {
        const total = (data / 50) + 1;
        for (let i = 1; i <= total; i++) {
            //This is a promise hell 
           getTracks(i * 50, access_token).then(moredata => {

            });
        }    
    });
    res.send(tracks);

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