FormTestPlaceholderForm.php

<?php

namespace Drupal\form_test\Form;

use Drupal\Core\Form\FormBase;
use Drupal\Core\Form\FormStateInterface;

/**
 * Builds a form to test the placeholder attribute.
 *
 * @internal
 */
class FormTestPlaceholderForm extends FormBase {
    
    /**
     * {@inheritdoc}
     */
    public function getFormId() {
        return 'form_test_placeholder_test';
    }
    
    /**
     * {@inheritdoc}
     */
    public function buildForm(array $form, FormStateInterface $form_state) {
        foreach ([
            'textfield',
            'textarea',
            'url',
            'password',
            'search',
            'tel',
            'email',
            'number',
        ] as $type) {
            $form[$type] = [
                '#type' => $type,
                '#title' => $type,
                '#placeholder' => 'placeholder-text',
            ];
        }
        return $form;
    }
    
    /**
     * {@inheritdoc}
     */
    public function submitForm(array &$form, FormStateInterface $form_state) {
    }

}