ambient.impact
--- a/core/assets/scaffold/files/default.settings.php
+++ b/core/assets/scaffold/files/default.settings.php
 # $settings['migrate_file_public_path'] = '';
 # $settings['migrate_file_private_path'] = '';

+/**
+ * JavaScript libraries with these attributes will be aggregated together.
+ */
+$settings['aggregated_js_attributes'] = ['defer', 'async'];
--- a/core/lib/Drupal/Core/Asset/JsCollectionGrouper.php
+++ b/core/lib/Drupal/Core/Asset/JsCollectionGrouper.php
          // Help ensure maximum reuse of aggregate files by only grouping
          // together items that share the same 'group' value.
          $group_keys = $item['preprocess'] ? [$item['type'], $item['group']] : FALSE;
+
+          // Enables aggregation for 'async' or 'defer' attributes.
+          if ($group_keys && !empty($item['attributes'])) {
+            foreach (array_keys($item['attributes']) as $attribute_key) {
+              if (in_array($attribute_key, Settings::get('aggregated_js_attributes', ['async', 'defer']))) {
+                $group_keys[] = $attribute_key;
+              }
+              else {
+                $group_keys = FALSE;