How to avoid nesting promises in Firebase Cloud Functions?

Question

I'm using this tutorial as a main way to learn about Dialogflow and Firebase, and I've gotten stuck in the following section of code:

25   if(action === 'firebase.update'){
26          let userId = 'marc.tuinier';
27          // Check if the user is in our DB
28          admin.firestore().collection('users').where('userId', '==', userId).limit(1).get()
29              .then(snapshot => {
30                  let user = snapshot.docs[0]
31                  if (!user) {
32                      // Add the user to DB
33                      admin.firestore().collection('users').add({
34                          userId: userId
35                      }).then(ref => {
36                          sendResponse('Added new user');
37                      });
38                  } else {
39                      // User in DB
40                      sendResponse('User already exists');
41                  }
42              });
43      }

I'm getting these errors:

 28:9   error    Expected catch() or return                  promise/catch-or-return
 31:17  error    Each then() should return a value or throw  promise/always-return
 33:21  error    Expected catch() or return                  promise/catch-or-return
 33:21  warning  Avoid nesting promises                      promise/no-nesting
 35:29  error    Each then() should return a value or throw  promise/always-return

I was predominantly wondering how to fix these errors (and perhaps some material so I can learn more about it - thanks in advance!)

Answer 1

So as far as avoiding nested promises I would recommend looking into async / await, leaving you with something like the following. You can then add try/catch blocks to debug further

if(action === 'firebase.update'){
       let userId = 'marc.tuinier';
       // Check if the user is in our DB
       let snapshot = await admin.firestore().collection('users').where('userId', '==', userId).limit(1).get()
       let user = snapshot.docs[0]
        if (!user) {
            // Add the user to DB
            await admin.firestore().collection('users').add({
                userId: userId
            })
            return sendResponse('Added new user');
        } else {
            return sendResponse('User already exists');
        }
   }