<?php $response = array('valid' => false, 'message' => 'This "user" does not exist.'); if (isset($_POST['user'])) { $userFactory = new UserFactory(DataStorage::instance()); $user = $userFactory->loadUser($_POST['user']); if ($user) { // User name is registered on another account $response = array('valid' => false, 'message' => 'This user name is already registered.'); } else { // User name is available $response = array('valid' => true); } } echo json_encode($response);