FormTestTextareaForm.php

<?php

declare (strict_types=1);
namespace Drupal\form_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;
use Symfony\Component\HttpFoundation\JsonResponse;

/**
 * Form for testing textarea.
 *
 * @internal
 */
class FormTestTextareaForm extends FormBase {
  
  /**
   * {@inheritdoc}
   */
  public function getFormId() {
    return '_test_textarea_form';
  }
  
  /**
   * {@inheritdoc}
   */
  public function buildForm(array $form, FormStateInterface $form_state) {
    foreach ([
      'vertical',
      'horizontal',
      'both',
      'none',
    ] as $resizableMode) {
      $id = 'textarea_resizable_' . $resizableMode;
      $form[$id] = [
        '#type' => 'textarea',
        '#title' => $id,
        '#resizable' => $resizableMode,
      ];
    }
    $form['submit'] = [
      '#type' => 'submit',
      '#value' => $this->t('Submit'),
    ];
    return $form;
  }
  
  /**
   * {@inheritdoc}
   */
  public function submitForm(array &$form, FormStateInterface $form_state) : void {
    $form_state->setResponse(new JsonResponse($form_state->getValues()));
  }

}