How can I check if user exists in Firebase?

Question

I finally got my authentication to work in terms of creating users and logging in and out. But now, I want to implement something that checks if the user already exists in Firebase. I've looked it up but can't seem to find a concrete answer.

For example, if my email address is: [email protected] and someone else tries to signup with the same email address, how do I tell them it's already taken?

login(e) {
    e.preventDefault();

    fire.auth().signInWithEmailAndPassword(this.state.email, this.state.password)
        .then((u) => {
        }).catch((error) => {
        console.log(error);
    });
}

signup(e) {
    e.preventDefault();

    fire.auth().createUserWithEmailAndPassword(this.state.email, this.state.password)
        .then((u) => {
        }).catch((error) => {
        console.log(error);
    });
}

duplicate? stackoverflow.com/questions/44615808/…

Chris Hawkes
– Chris Hawkes

2018-07-27 18:13:22 +00:00
Commented Jul 27, 2018 at 18:13 — Chris Hawkes
– Chris Hawkes, Commented Jul 27, 2018 at 18:13
Possible duplicate of Firebase Detecting if user exists

Mathews Sunny
– Mathews Sunny

2018-07-27 18:15:12 +00:00
Commented Jul 27, 2018 at 18:15 — Mathews Sunny
– Mathews Sunny, Commented Jul 27, 2018 at 18:15

Kid · Accepted Answer · 2020-07-23 16:25:33Z

39

The error that is returned from method createUserWithEmailAndPassword has a code property. Per the documentation the error code auth/email-already-in-use:

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

At very minimum you can utilize conditional statements such as if/else or switch to check for that code and display/log/dispatch/etc a message or code to the user:

fire.auth().createUserWithEmailAndPassword(this.state.email, this.state.password)
  .then(u => {})
  .catch(error => {
     switch (error.code) {
        case 'auth/email-already-in-use':
          console.log(`Email address ${this.state.email} already in use.`);
          break;
        case 'auth/invalid-email':
          console.log(`Email address ${this.state.email} is invalid.`);
          break;
        case 'auth/operation-not-allowed':
          console.log(`Error during sign up.`);
          break;
        case 'auth/weak-password':
          console.log('Password is not strong enough. Add additional characters including special characters and numbers.');
          break;
        default:
          console.log(error.message);
          break;
      }
  });

Hopefully that helps!

edited Jul 23, 2020 at 16:25

Kid

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answered Jul 27, 2018 at 17:48

Alexander Staroselsky

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1 Comment

Kid Over a year ago

Checking inside a catch is correct, but you are missing break in the switch.

hakobpogh · Accepted Answer · 2022-04-06 15:29:53Z

25

There's a simpler answer in the case of firebase admin sdk:

const uidExists = auth().getUser(uid).then(() => true).catch(() => false))

const emailExists = auth().getUserByEmail(email).then(() => true).catch(() => false))

edited Apr 6, 2022 at 15:29

hakobpogh

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answered Jul 4, 2020 at 12:49

Arutyun Enfendzhyan

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2 Comments

Marc Van Daele Over a year ago

note that these only work server side (admin SDK), not client side.

Ollie Over a year ago

This could be improved by checking for err.code === "auth/user-not-found". getUser could fail for other reasons.

Dustin Spengler · Accepted Answer · 2023-12-13 16:20:45Z

11

I use fetchSignInMethodsForEmail like this:

import { getAuth, fetchSignInMethodsForEmail } from 'firebase/auth';

const auth = getAuth();
let signInMethods = await fetchSignInMethodsForEmail(auth, email);
if (signInMethods.length > 0) {
  //user exists
} else {
   //user does not exist
}

Docs for reference

Update Sept 15 2023: Firebase now disables this feature by default to avoid Email Enumerarion. According to Google:

Email enumeration is a type of brute-force attack in which a malicious actor attempts to guess or confirm users in a system by passing an email address to the API and checking the response.

You can still use this feature by enabling it in your Firebase console by navigating to Authentication -> Settings -> User Actions and then disabling email enumeration protection:

Make sure to read about the risk of disabling this on your platform

edited Dec 13, 2023 at 16:20

answered Feb 12, 2023 at 17:20

Dustin Spengler

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7 Comments

user18759118 Over a year ago

I don't know if this is a ideal way as it requires auth isntance. the OP is wanting to check if user exists in logged out state in which I don't think this answer would work

Dustin Spengler Over a year ago

@rbtmr Thats not true. The question states "I want to implement something that checks if the user already exists in Firebase". Thanks for the downvote broski.

user18759118 Over a year ago

@DustinSpengler "For example, if my email address is: [email protected] and someone else tries to signup with the same email address, how do I tell them it's already taken?"

user18759118 Over a year ago

@DustinSpengler no it doesnt. i ran into the same issue last month, cloud.google.com/identity-platform/docs/admin/…

user18759118 Over a year ago

"A list of sign-in methods for a specified email address is no longer returned when calling the createAuthUri REST API or the fetchSignInMethodsForEmail client SDK method on all platforms."

|

Balanagu Yashwanth · Accepted Answer · 2020-10-17 11:02:38Z

0

from firebase_admin import auth

user = auth.get_user_by_email(email)
print('Successfully fetched user data exists: {0}'.format(user.uid))

In python admin server

answered Oct 17, 2020 at 11:02

Balanagu Yashwanth

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