I Want To Check If User Exist Before Login If Not They Must Sign Up, In Firebase Google Auth

Question

I have Login and Sign Up functionality using Firebase Google Auth and It works Fine but I want to Check If the user already Signed Up, They can't sign Up 2 times they'll have to Login. is there a Code Like:

if(user.exist){
  alert("Account Already exists please Login")
}else{
  auth.signInWithPopup(provider)
}

And vice versa if they do not exist they'll have to Sign Up:

Is This possible with google auth?

Answer 1

You'll need to know at least part of the user's credentials to check if they already exist in Firebase Authentication.

For example, if the user signed in with a provider that requires their email before, you'll should ask them for their email address next time and then call fetchSignInMethodsForEmail to determine if Firebase already has a user for that email address.