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()));
    }

}