Cloud Functions -How to Update Multiple Refs - firebase-realtime-database

Question

I have to fetch data at a couple of refs and update at a couple of refs. Everything works fine except for the fourth ref loopArrAtFourthRef that I have to update. It gets it's values from the third via a loop. The problem is the fifthRef finishes before the fourth ref. I'm a Swift dev and I can't get the hang of Promises, they are way to foreign for me.
exports.updateMultipleRefs = functions.https.onCall((data, context) => {
// ... values from data used in refs
const fetchFromFirstRef = admin.database()....
const updateAtSecondRef = admin.database()....
const runTransactionAtSecondRef = admin.database()....
const fetchArrDataFromThirdRef = admin.database()....
const loopArrAtFourthRef = admin.database()....
const updateFifthRef = admin.database()....
var arr = [];
var promises = [];
var val_1 = 0;
var val_2 = 0;
return fetchFromFirstRef
.once('value')
.then((snapshot) => {
if (snapshot.exists()) {
snapshot.forEach((childSnapshot) => {
// val_1 += data from each childSnapshot
});
return updateAtSecondRef.update({ "val_1":val_1 }).then(()=> {
return runTransactionAtSecondRef.set(admin.database.ServerValue.increment(1));
}).then(() => {
return fetchArrDataFromThirdRef
.once('value')
.then((snapshot) => {
if (snapshot.exists()) {
snapshot.forEach((childSnapshot) => {
var gameId = childSnapshot.key;
arr.push(gameId);
});
} else {
return null;
}
});
}).then(() => {
// this is where I'm having the problem, the fifth ref finishes before this does
for (var i = 0; i < arr.length; i++) {
var gameId = arr[i];
var promiseRef = loopArrAtFourthRef.child(gameId);
promises.push(promiseRef.once('value').then((snap) => {
snap.forEach((child) => {
// val_2 += data from each child
});
}));
return Promise.all(promises);
}
}).then(() => {
return updateFifthRef.update({ "val_2": val_2 });
});
} else {
return null;
}
})
.catch((error) => {
console.log('error', error);
return null;
});
});

Answer 1

Following this answer and this blog I just had to create an array of Promises and run Promise.all() after the outer for-loop finished:
for (var i = 0; i < arr.length; i++) {
var gameId = arr[i];
var promiseRef = loopArrAtFourthRef.child(gameId);
promises.push(promiseRef.once('value').then((snap) => {
snap.forEach((child) => {
// val_2 += data from each child
});
}));
}
return Promise.all(promises);