materio-d8/web/modules/custom/vue_link_formatter/vue_link_formatter.module

<?php

/**
 * @file
 * Defines simple link field types.
 */

use Drupal\Core\Routing\RouteMatchInterface;
use Drupal\Core\Link;
use Drupal\Core\Template\Attribute;

/**
 * Implements hook_theme().
 */
function vue_link_formatter_theme() {
  return [
    'link_formatter_vue_link_formatter' => [
      'variables' => [
        'title' => NULL,
        'url_title' => NULL,
        'url' => NULL,
        'methode' => NULL,
        'event_modifiers' => NULL,
      ],
    ],
  ];
}

/**
 * Prepares variables for button link field templates.
 *
 * This template outputs a separate title and link.
 *
 * Default template: link-formatter-button-link.html.twig.
 *
 * @param array $variables
 *   An associative array containing:
 *   - title: (optional) A descriptive or alternate title for the link, which
 *     may be different than the actual link text.
 *   - url_title: The anchor text for the link.
 *   - url: A \Drupal\Core\Url object.
 */
function template_preprocess_link_formatter_vue_link_formatter(&$variables) {
  $url = $variables['url'];
  $attributes = $url->getOption('attributes');
  $attributes['class'][] = 'btn';
  $attributes['href'] = $url->toString();

  $modifiers = [];
  foreach ($variables['event_modifiers'] as $modifier => $value) {
    if ($value) {
      $modifiers[] = $modifier;
    }
  }
  $attributes['@click.' . implode('.', $modifiers)] = $variables['methode'];

  $url->setOption('attributes', $attributes);
  $variables['link'] = Link::fromTextAndUrl($variables['title'], $url )->toString();
  $variables['attributes'] = new Attribute($attributes);
}