Firebase - what is the most efficient way to check if an email is registered?

问题

I'm trying to write a function that will check to see if an email is registered with my Firebase app (with Javascript/Web), before proceeding with the sign up process (if the email isn't registered).

I created a node named active_emails which I wanted to populate with registered emails (like an array). I was going to check the email against this list and if it didn't exist then I would allow the user to proceed with the registration process.

I see from the answer here: Proper way to store values array-like in Firebase that Firebase creates keys inside the array. So a normal Javascript array check won't work. I understand how the answer above works, but I was wondering, since I'm essentially doing a look up on the emails of registered Firebase users, is there another way to do this check?

Am I correct in thinking that the answer above requires Firebase to compile and then send an array of emails back to the user client-side? This seems like it might affect performance (if there are hundreds of thousands, or millions of emails on file), and would it expose all user emails to the client? Is there another way to check if a user is registered or not, maybe something like attempting a registration and then catching a duplicate email error (although this sounds like a messy way to go about this).

The top answer here: How to find out if an email is already registered with Firebase Simple Login? suggests using fetchProvidersForEmail as a way of checking to see if an email is registered, but that answer is for android and I don't know if it's possible to do such a thing with Javascript/Web.

I've tried to integrate this method here:

    function checkEmail(){
        firebase.database().ref().fetchProvidersForEmail("emailaddress@gmail.com").once("value", function(snapshot) {
        console.log(snapshot);
    }); 
}   

But it shows the error: firebase.database(...).ref(...).fetchProvidersForEmail is not a function. Does anybody have any ideas on the best way to go about achieving this check?

Thank you in advance!

回答1:

This method is for auth only: firebase.auth().fetchProvidersForEmail("emailaddress@gmail.com")

来源：https://stackoverflow.com/questions/41039986/firebase-what-is-the-most-efficient-way-to-check-if-an-email-is-registered