TypeError: Cannot read property 'then' of undefined although function returns promise

Question

class Firebase {
  constructor() {
    app.initializeApp(firebaseConfig);
    this.auth = app.auth();
  }

  doCreateUserWithEmailAndPassword = (email, password) => {
   this.auth.createUserWithEmailAndPassword(email, password);
  };
}

When calling the Firebase.doCreateUserWithEmailAndPassword()-method with .then() I get the following error method:

TypeError: Cannot read property 'then' of undefined

Answer 1

I think many starters face this problem so I thought to share my solution.

The { } around of the doCreateUserWithEmailAndPassword-method should have been removed so that the result of this.auth.createUserWithEmailAndPassword() is returned, because of the arrow function syntax

or

I could have kept the { } and added a return statement.

So the right way would have been either:

 doCreateUserWithEmailAndPassword = (email, password) => 
    this.auth.createUserWithEmailAndPassword(email, password);

or

 doCreateUserWithEmailAndPassword = (email, password) => {
    return this.auth.createUserWithEmailAndPassword(email, password);
  };