Overwritten register_content.html.twig

<script>
    function registrationSubmit() {
        $.post( '{{ path( 'onn_user_registration_register', { 'active': 'yes' }) }}',
                $('#form_registration').serialize(),
                function(data){
                    $('#registration').empty().append(data);
                    $('#result_registration').empty().append('Submitted');
                    var erase_result = function() { $('#result_registration').empty(); }
                    setTimeout(erase_result, 2000);
                }
        );
        return false;
    }
</script>
<div id="registration">
    {% set form_message = app.session.get('form_message') %}

    {% if form_message|length > 0 %}
        <div class="alert alert-error">
            {{ form_message }}
        </div>
    {% endif %}

    <form id='form_registration' method="post" {{ form_enctype(form) }} name="registration" >
        {{ form_widget(form) }}
        <button onclick='registrationSubmit()' value='Submit' class="btn btn-large btn-success" style="margin:10px;">Create New Account</button>
    </form>

    <div id='result_registration'></div>
</div>

Overwritten RegistrationController

<?php

namespace ONN\UserBundle\Controller;

use FOS\UserBundle\FOSUserEvents;
use FOS\UserBundle\Event\FormEvent;
use FOS\UserBundle\Event\GetResponseUserEvent;
use FOS\UserBundle\Event\FilterUserResponseEvent;
use Symfony\Component\HttpFoundation\Request;
use Symfony\Component\HttpFoundation\RedirectResponse;
use FOS\UserBundle\Controller\RegistrationController as BaseController;

class RegistrationController extends BaseController
{
    public function registerAction(Request $request,$active = null)
    {
        if ($active != null){
            throw new \Exception('registerAction reached');
        }
        /** @var $formFactory \FOS\UserBundle\Form\Factory\FactoryInterface */
        $formFactory = $this->container->get('fos_user.registration.form.factory');
        /** @var $userManager \FOS\UserBundle\Model\UserManagerInterface */
        $userManager = $this->container->get('fos_user.user_manager');
        /** @var $dispatcher \Symfony\Component\EventDispatcher\EventDispatcherInterface */
        $dispatcher = $this->container->get('event_dispatcher');

        $user = $userManager->createUser();
        $user->setEnabled(true);

        $event = new GetResponseUserEvent($user, $request);
        $dispatcher->dispatch(FOSUserEvents::REGISTRATION_INITIALIZE, $event);

        if (null !== $event->getResponse()) {
            //var_dump($event->getResponse());
            //throw new \Exception("event");
            return $event->getResponse();
        }

        $form = $formFactory->createForm();
        $form->setData($user);

        if ($active == 'yes') {
            throw new \Exception('yes');
            $form->bind($request);

            if ($form->isValid()) {
                $event = new FormEvent($form, $request);
                $dispatcher->dispatch(FOSUserEvents::REGISTRATION_SUCCESS, $event);

                $userManager->updateUser($user);

                if (null === $response = $event->getResponse()) {
                    $url = $this->container->get('router')->generate('fos_user_registration_confirmed');
                    $response = new RedirectResponse($url);
                }

                $dispatcher->dispatch(FOSUserEvents::REGISTRATION_COMPLETED, new FilterUserResponseEvent($user, $request, $response));

                return $response;
            }
        }
        return $this->container->get('templating')->renderResponse('ONNUserBundle:Registration:register.html.twig', array(
                'form' => $form->createView(),
            ));
    }
}