Handle Observers in onAuthStateChanged

[wSedlacek]

In this section

mockbase/auth/auth.ts

Lines 67 to 78 in 61b9467

	onAuthStateChanged(
	nextOrObserver: AuthStateChangeListener,
	error?: (a: firebase.auth.Error) => void,
	completed?: firebase.Unsubscribe
	): firebase.Unsubscribe {
	this.authStateEvents.add(nextOrObserver);
	nextOrObserver(this.currentUser);
	return () => {
	this.authStateEvents.delete(nextOrObserver);
	};
	}

When used with

  public readonly authState = new Observable<User | null>(
    this.auth.onAuthStateChanged.bind(this.auth)
  );

as done in
https://github.com/angular/angularfire/blob/2de8501d10add9e575885db9f44b8098e5857929/src/auth/auth.ts#L66

throws the following error.

TypeError: nextOrObserver is not a function

It should be noted that nextOrObserver is a SwitchMapSubscriber when this error occurs.

Reference:
https://github.com/ReactiveX/rxjs/blob/b8c2a52bf78e855dfe48e3620b7ee2fee05ec120/src/internal/operators/switchMap.ts#L109

Simply checking typeof should allow us to determine if nextOrObserver is next or observer
observer seem to be expecting you to call nest() on them with the user.

Here is the firebase implementation of this function for additional reference
https://github.com/firebase/firebase-js-sdk/blob/35bc0a2eea98d9796023f15cd5783700d45ccc4d/packages/auth/src/auth.js#L1442-L1472