Detect if an email already exists in firebase

Question

I have the following in my FireBase database:

Users
 -VCVVsqwws_QSds2ADC1
    email: 
      "lo@aol.com"
 -VCVxCaQ_dSwWBC21AB4
    email: 
      "asdasasd@aaa.com"

and then the lines in my .js file:

firebase.initializeApp(config);
var register = firebase.database().ref("Users");

How can I check if Users already contains an email before pushing it to Users ? I tried to follow https://gist.github.com/anantn/4323949 but the browser says cannot instantiate Firebase (new Firebase) even though everything is imported and included.

Answer 1

You can use the following code:

var register = firebase.database().ref("Users/{{userId}}");

register.once('value', function(snapshot) {
   if(snapshot.val().hasOwnProperty('email')) {
     console.log("Email exist.");
   }
   else {
     console.log("Email not exist.");
     /* Code to push email to the specific user */
   }
});

Answer 2

You can also use the following code (trigger warning: es6) if you need to check only one user really fast:

firebase.database().ref(`Users/${userId}`)once('value').then(snapshot => {
   if(snapshot.val().hasOwnProperty('email')) {
     console.log("Email exists.");
   }
   else {
     console.log("Email doesn't exist.");
     /* Code to push email to the specific user */
   }
});

Note that ti2005's snippet works perfectly well but it will load all users and that process will get slower as your database grows.