Problem with onAuthStateChanged (React & Firebase)

Question

I'm using firebase and i want to solve problem with delay. When I'm refreshing currentUser is setting to null and my component is not showing but after 2 sec it is working correctly. Here is code:

Code example:

type FirebaseUserState = User | null;

export function useAuth() {
  let [currentUser, setUser] = useState<FirebaseUserState>(null);

  auth.onAuthStateChanged((user) => {
    if (user !== null) {
      setUser(user);
    }
  });
  return currentUser;
}