Answer by Chris for Firestore listener subscription triggers random number of times

Well I've solved my actual problem by setting a timestamp on the object via another firestore listener, then comparing the current and previous to only trigger once.

I'll post this code if anyone comes here doing a similar thing, but I'd still want to find out why my subscriber is going off so many times.

Cloud function:

export class UserUpdateListener {  public listen = functions.firestore    .document('user/{uid}')    .onWrite(async (snapshot) => {      const before: User = snapshot.before.data() as User;      const after: User = snapshot.after.data() as User;      const skipUpdate = before.lastUpdate && after.lastUpdate && !before.lastUpdate.isEqual(after.lastUpdate);      if (skipUpdate) {        functions.logger.info('No changes, skipping timestamp update');        return;      }      await snapshot.after.ref.update({ lastUpdate: admin.firestore.FieldValue.serverTimestamp() });    });}

I then check the timestamp in my client using:

constructor(private angularFireAuth: AngularFireAuth, private firestore: AngularFirestore, private router: Router) {  this.onAuthStateChanged();  let lastUpdate: Timestamp;  this.user$.subscribe(async (user) => {    if (this.authUser && user && user.lastUpdate) {      if (lastUpdate && !user.lastUpdate.isEqual(lastUpdate)) {        await this.authUser.getIdToken(true);      }      lastUpdate = user.lastUpdate;    }  });}

Hopefully this will save someone some time.