Drupal → AJAX submit с поддержкой валидации

class ExampleForm extends FormBase {
 
  /**
   * {@inheritDoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    $form['testfield'] = [
      '#type' => 'textfield',
      '#title' => 'Testfield',
      '#required' => TRUE,
    ];
 
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => 'Submit',
      '#ajax' => [
        'callback' => '::ajaxSubmit',
        'wrapper' => Html::getId($this->getFormId()),
      ],
    ];
 
    $form['submit']['#ajax']['callback'] = '::ajaxSubmit';
 
    $form['#id'] = Html::getId($this->getFormId());
 
    return $form;
  }
 
  /**
   * Ajax submit.
   */
  public function ajaxSubmit(array &$form, FormStateInterface $form_state) {
    if ($form_state->hasAnyErrors()) {
      return $form;
    }
 
    return ['#markup' => 'Form submitted'];
  }
 
}

/**
 * Form builder.
 */
function modulename_testform($form, &$form_state) {
  $form['testfield'] = array(
    '#type' => 'textfield',
    '#title' => 'Testfield',
    '#required' => TRUE,
  );
 
  $form['submit'] = array(
    '#type' => 'submit',
    '#value' => 'Submit',
    '#ajax' => array(
      'callback' => 'modulename_testform_ajax_submit',
      'wrapper' => 'modulename-testform',
    ),
  );
 
  return $form;
}
 
/**
 * Ajax submit.
 */
function modulename_testform_ajax_submit($form, &$form_state) {
  if (form_get_errors()) {
    return $form;
  }
  else {
    return 'Form submitted';
  }
}