AjaxTestCommandReturnPromise example

return $form;
  }

  /** * Ajax callback for the "Execute commands button" button. */
  public static function executeCommands(array $form, FormStateInterface $form_state) {
    $selector = '#ajax_test_form_promise_wrapper';
    $response = new AjaxResponse();

    $response->addCommand(new AppendCommand($selector, '1'));
    $response->addCommand(new AjaxTestCommandReturnPromise($selector, '2'));
    $response->addCommand(new AppendCommand($selector, '3'));
    $response->addCommand(new AppendCommand($selector, '4'));
    $response->addCommand(new AjaxTestCommandReturnPromise($selector, '5'));

    return $response;
  }

  /** * {@inheritdoc} */
  public function submitForm(array &$form, FormStateInterface $form_state) {