Firebase Authentication : Lookup a user by Email

I use fetchProvidersForEmail(email) and if the result return as empty array then, this email hasn't been use to sign up.

firebase.auth().fetchProvidersForEmail(email)
.then(providers => {
  if (providers.length === 0) {
    // this email hasn't signed up yet
  } else {
    // has signed up
  }
});

The new method of creating users with email password returns a value whether the given email address is already in use. See here