Property does not exist on type 'function'

I am trying to use the firebase.auth method in a function using typescript and I am getting a Property 'name' does not exist on type 'Function' (ts 2339). I must be missing something simple here, however not quite sure what it is.

const registerUser = (email: String, password: String) => {  console.log(email, password);  return (firebase.auth as Function)    .createUserWithEmailAndPassword(email, password)    .then((userObj: Object) => console.log(email, password, userObj))    .catch((error: Error) => console.log('Error logging in.', error));};

The problem happens with the .createUserWithEmailAndPassword

PROBLEM SOLVED: I tried to solve the problem by casting firebase.auth as type Function, it is easily solved by removing that and calling it by firebase.auth()