Drupal 8 Adding a Reset Button to a form

drupal-8.form.reset-button.php

<?php
/**
 * Implements template_preprocess_form().
 */
function TEMPLATE_preprocess_form(&$vars) {
  $vars['form']['actions']['reset'] = [
    '#type' => 'html_tag',
    '#tag' => 'input',
    '#attributes' => [
      'class' => 'button',
      'type' => 'reset',
      'value' => t('Reset'),
    ],
  ];
}

Thanks a lot! Very helpful.

Thank you! :)

I still think Core should add reset and button as FAPI types, but that's a different topic.

Perhaps you'd like to translate the value?
'value' => $this->t('Reset'),

@JPustkuchen thanks for your suggestion. I update the gist.
If you need more example you can find them in the core:

• PathFilterForm::buildForm
• DblogFilterForm::buildForm

  // Example from \Drupal\dblog\Form\DblogFilterForm.
  public function buildForm(array $form, FormStateInterface $form_state) {
    //...
    if (!empty($session_filters)) {
      $form['filters']['actions']['reset'] = [
        '#type' => 'submit',
        '#value' => $this->t('Reset'),
        '#limit_validation_errors' => [],
        // callback to reset form values.
        '#submit' => ['::resetForm'],
      ];
    }
    //...
  }

  public function resetForm(array &$form, FormStateInterface $form_state) {
    $this->getRequest()->getSession()->remove('dblog_overview_filter');
  }