I am using jQuery to edit my form which is built in Symfony.
I am showing the form in jQuery dialog and then submitting it.
Since Symfony 3.1 you can use JSON Helper http://symfony.com/doc/current/book/controller.html#json-helper
public function indexAction()
{
// returns '{"username":"jane.doe"}' and sets the proper Content-Type header
return $this->json(array('username' => 'jane.doe'));
// the shortcut defines three optional arguments
// return $this->json($data, $status = 200, $headers = array(), $context = array());
}