Firebase Detecting if user exists

Question

How Can I Check user exists in Firebase auth in Signup Button via react native?

This is my Login Page Code:

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Answer 1

For me fetchSignInMethodsForEmail() only works with an email that is registered with email/password and not working for emails registered with Apple, LinkedIn or other providers.

For solution to this, I came up with following work around:

auth().signInWithEmailAndPassword(email, 'some-random-password')  // Password should be really long to avoid actually logging in :)
.then((response) => {
    // TODO : Avoid this block
})
.catch((error) => {
    if(error.code === 'auth/wrong-password'){
        // TODO : If here then it means account already exists...
    }

    if(error.code === 'auth/user-not-found'){
        // TODO : If here then you guessed it... you can create a new account.
    }
})

I'm sure there is a proper solution for this and I will update this answer when I find it.

Hope this will help someone

Answer 2

Here's how to use the fetchSignInMethodsForEmail API. It returns an array. If the array is empty, it means the user has never signed up/signed in to your app with the sign in methods you have used in your app.

This is an example with Google signin.

firebase
    .auth()
    .signInWithPopup(provider)
    .then((result) => {
        let token = result.credential.accessToken;
        let user = result.user;

        firebase
            .auth()
            .fetchSignInMethodsForEmail(user.email)
            .then((result) => {
                console.log('result', result);
            });
        })
        .catch((error) => {
            // Handle Errors here.
        }

Answer 3

It is very simple. Add a then() and catch() to your firebase method in signUp function.

firebase.auth().createUserWithEmailAndPassword(this.state.email, this.state.password)
.then(()=>{
    console.log('Signup successful.');
    this.setState({
            response: 'Account Created!'
        })
   })
.catch((error)=> {
    console.log(error.code);
    console.log(error.message);
  });

Information on different Error Codes:

• auth/email-already-in-use

  Thrown if there already exists an account with the given email address.

• auth/invalid-email

  Thrown if the email address is not valid.

• auth/operation-not-allowed

  Thrown if email/password accounts are not enabled. Enable email/password accounts in the Firebase Console, under the Auth tab.

• auth/weak-password

  Thrown if the password is not strong enough.

Answer 4

You need to use the fetchSignInMethodsForEmail API. It takes an email and returns a promise that resolves with the list of providers linked to that email if it is already registered: https://firebase.google.com/docs/reference/js/firebase.auth.Auth.html#fetchsigninmethodsforemail