Drupal 8 - Ajouter des variables à l'objet javascript DrupalSettings

Via le hook hook_page_attachments() :

/**
 * Implements hook_page_attachments().
 *
 * Add custom variables to DrupalSettings.
 */
function MODULE_page_attachments(array &$attachments) {
  $attachments['#attached']['drupalSettings']['basepath'] = base_path();
  $attachments['#attached']['drupalSettings']['pathtotheme'] = base_path() . drupal_get_path('theme', \Drupal::theme()->getActiveTheme()->getName());
  $attachments['#attached']['drupalSettings']['pathtotfiles'] = PublicStream::basePath();
}