如何在Symfony2表单中向CollectionType添加行？

use Symfony\Component\Form\Extension\Core\Type\CollectionType;
use AppBundle\Form\Type\ContactType;

// ...

$builder->add('contacts', CollectionType::class, [
    'entry_type' => ContactType::class,
    'allow_add' => true,
    'allow_delete' => true,
    'by_reference' => false,
]);

{{ form_start(form) }}

<div id="contacts">
    {% for contactForm in form.contacts %}
        {{ form_row(contactForm.name) }}
        {{ form_row(contactForm.email) }}
        {{ form_row(contactForm.phone) }}
    {% endfor %}
</div>

<button type="button" class="add-contact">Add Contact</button>

{{ form_end(form) }}

<script>
    var $contactsContainer = $('#contacts');
    var $addContactButton = $('.add-contact');

    $addContactButton.on('click', function() {
        var prototype = $contactsContainer.data('prototype');
        var index = $contactsContainer.data('index');
        var newForm = prototype.replace(/__name__/g, index);

        $contactsContainer.append(newForm);
        $contactsContainer.data('index', index + 1);
    });
</script>