Issue #3140556: Drupal 9 compatibility

src/Form/JstimerAdminSettings.php

@@ -10,6 +10,7 @@ namespace Drupal\jstimer\Form;
 use Drupal\Core\Form\ConfigFormBase;
 use Drupal\Core\Form\FormStateInterface;
 use Drupal\Core\Render\Element;
+use \Drupal\Core\Asset\JsCollectionOptimizer;
 
 class JstimerAdminSettings extends ConfigFormBase {
 
@@ -67,6 +68,7 @@ class JstimerAdminSettings extends ConfigFormBase {
   public function _submitForm(array &$form, FormStateInterface $form_state) {
     // build timer.js file with new settings.
     jstimer_build_js_cache();
-	drupal_clear_js_cache();
+    $js = \Drupal::service('asset.js.collection_optimizer');
+    $js->deleteAll();
   }
 }