successfulAjaxSubmit example

public function ajaxSubmit(array &$form, FormStateInterface $form_state) {
    if ($form_state->hasAnyErrors()) {
      $form['status_messages'] = [
        '#type' => 'status_messages',
        '#weight' => -1000,
      ];
      $form['#sorted'] = FALSE;
      $response = new AjaxResponse();
      $response->addCommand(new ReplaceCommand('[data-drupal-selector="' . $form['#attributes']['data-drupal-selector'] . '"]', $form));
    }
    else {
      $response = $this->successfulAjaxSubmit($form, $form_state);
    }
    return $response;
  }

  /** * Allows the form to respond to a successful AJAX submission. * * @param array $form * An associative array containing the structure of the form. * @param \Drupal\Core\Form\FormStateInterface $form_state * The current state of the form. * * @return \Drupal\Core\Ajax\AjaxResponse * An AJAX response. */