Enforce no duplicate emails in Firebase

no_dup_emails.js

/**
 * My Firebase data structure:
 * 
 *   /email_index/$email/user_id
 *   /user/$user_id/email
 */

var fb = new Firebase(URL);

function isDuplicateEmail(email, callback) {
  fb.child('email_index/'+escapeEmail(email)).once('value', function(snap) {
     callback( snap.val() !== null );
  });
}

function updateUser(user_id, email) {
   fb.child('user/'+user_id).set({email: email});
   fb.child('email_index/'+escapeEmail(email)).set(user_id);
}

function escapeEmail(email) {
  return (email || '').replace('.', ',');
}

To replace all occurrences.

function escapeEmail(email) { return (email || '').replace(/\./g, ','); }