CODE EXAMPLE FOR JAVASCRIPT

check change from service variable angular

export class UserService {

userDocumentReady: boolean = false; // initial value is "userdoc is not ready"
userDocObserver: Subject<boolean> = new Subject<boolean>(); // observing that bool

constructor(
  public fireauth: AngularFireAuth,
  public afs: AngularFirestore,
) {

// watch variable
this.userDocObserver.subscribe(value => this.userDocumentReady = value);

this.fireauth.authState
  .subscribe(user => {
    if (user) {

      this.afs.doc(`/tooluser/${user.uid}`).snapshotChanges()
      .subscribe(usr => {
        if (usr.payload.data()) {
          console.log(`got user object from database:`, usr.payload.data());              
          this.currentUser = usr.payload.data();

          this.userDocObserver.next(true); // flip UserDocumentReady flag