Check If Firebase User Exist Without Throwing Error

Question

I have a website that offers a simple messaging service. Individuals can pay for the service, or a business can pay for a monthly subscription and then add their clients/users for free. When the business adds a client/user email, that triggers the function below. I'm using firebase functions and createUser to create the user on my server(less). However, sometimes a business tries to register a user and that user already exist. In this case, I want to send the user a reminder email.

The code I have works fine, but it feels funky having a chain within my catch/error. Is there another way to detect if an email is already registered with a Firebase account that won't throw an error?

exports.newUserRegisteredByBusiness = functions.database.ref('users/{uid}/users/invited/{shortEmail}').onWrite( (data, context) => {

//don't run function if data is null
if (!data.after.val()){
  console.log('SKIP: newUserRegisteredByBusiness null so skipping')
  return null
} else {

  let businessUID = context.params.uid
  let email = data.after.val()
  let shortEmail = context.params.shortEmail
  let password // =  something I randomly generate

  return admin.auth().createUser({ email: email, password: password}).then( (user)=> {

      //write new user data
      let updates = {}
      let userData // = stuff I need for service to run
      updates['users/' + user.uid ] = userData;
      return admin.database().ref().update(updates)
    }).then( () =>{

      //email new user about their new account
      return emailFunctions.newUserRegisteredByBusiness(email, password)

    }).catch( (error) =>{
      //if user already exist we will get error here.
      if (error.code === 'auth/email-already-exists'){
         //email and remind user about account
        return emailFunctions.remindUsersAccountWasCreated(email).then( ()=> {
          //Once email sends, delete the rtbd invite value that triggered this whole function
          //THIS IS WHERE MY CODE FEELS FUNKY! Is it ok to have this chain?
          return admin.database().ref('users/' + businessUID + '/users/invited/' + shortEmail).set(null)
        })
      } else {

        //delete the rtbd value that triggered this whole function
        return admin.database().ref('users/' + businessUID + '/users/invited/' + shortEmail).set(null)

      }


    });

  }
})

Answer 1

To find if a user account was already created for a given email address, you call admin.auth().getUserByEmail.

admin.auth().getUserByEmail(email).then(user => { 
  // User already exists
}).catch(err => { 
  if (err.code === 'auth/user-not-found') {
    // User doesn't exist yet, create it...
  }
})

While you're still using a catch() it feels like a much less failed operation.

Answer 2

To avoid further implementation in the catch block you can wrap this Firebase function into this code:

async function checkUserInFirebase(email) {
    return new Promise((resolve) => {
        admin.auth().getUserByEmail(email)
            .then((user) => {
                resolve({ isError: false, doesExist: true, user });
            })
            .catch((err) => {
                resolve({ isError: true, err });
            });
    });
}

...

const rFirebase = await checkUserInFirebase('[email protected]');