Flarum\Event\ConfigureWebApp::addAssets PHP Method

    public function addAssets($files)
    {
        foreach ((array) $files as $file) {
            $ext = pathinfo($file, PATHINFO_EXTENSION);
            switch ($ext) {
                case 'js':
                    $this->view->getJs()->addFile($file);
                    break;
                case 'css':
                case 'less':
                    $this->view->getCss()->addFile($file);
                    break;
            }
        }
    }

 /**
  * @param ConfigureClientView $event
  */
 public function addAssets(ConfigureWebApp $event)
 {
     if ($event->isForum()) {
         $event->addAssets([__DIR__ . '/../../js/forum/dist/extension.js', __DIR__ . '/../../less/forum/extension.less']);
         $event->addBootstrapper('flarum/lock/main');
     }
     if ($event->isAdmin()) {
         $event->addAssets([__DIR__ . '/../../js/admin/dist/extension.js']);
         $event->addBootstrapper('flarum/lock/main');
     }
 }