Request a unique username in Firebase

Question

I am new with Firebase. I am developing an angular + firebase application, where after registering a user by email + password, he can save his username after sending the profile form.

Before that, I want to know if the user in the application has his username. This aproch does not work, because scope.used is always false:

scope.used = false; scope.updateProfile = function(profile) { var ref = new Firebase(FIREBASE_URL + '/users'); ref.orderByChild("username").equalTo(profile.username).on("child_added", function(snapshot) { if (currentUser != snapshot.key()) { scope.used = true; } }); if (scope.used) { console.log('username already exists'); } }; 

Is there any other way to do this?

EDIT (I answer to myself)

This approach works:

  scope.used = false; var userRef = new Firebase(FIREBASE_URL + '/users/' + currentUser); scope.updateProfile = function(profile) { var ref = new Firebase(FIREBASE_URL + '/users'); ref.orderByChild("username").equalTo(profile.username).on("child_added", function(snapshot) { if (currentUser != snapshot.key()) { scope.used = true; } }); ref.orderByChild("username").equalTo(profile.username).once("value", function(snap) { //console.log("initial data loaded!", Object.keys(snap.val()).length === count); if (scope.used) { console.log('username already exists'); scope.used = false; }else{ console.log('username doesnt exists, update it'); userRef.child('username').set(profile.username); } }); };