diff --git a/src/Asset/RetrofitJsCollectionRenderer.php b/src/Asset/RetrofitJsCollectionRenderer.php
new file mode 100644
index 00000000..ba7eaa2d
--- /dev/null
+++ b/src/Asset/RetrofitJsCollectionRenderer.php
@@ -0,0 +1,53 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Retrofit\Drupal\Asset;
+
+use Drupal\Core\Asset\AssetCollectionRendererInterface;
+
+class RetrofitJsCollectionRenderer implements AssetCollectionRendererInterface
+{
+    /**
+     * @var array<array{
+     *   '#type': string,
+     *   '#tag': string,
+     *   '#value'?: string,
+     *   '#attributes'?: mixed[],
+     * }>
+     */
+    protected array $retrofitFooter = [];
+
+    public function __construct(
+        private readonly AssetCollectionRendererInterface $inner,
+    ) {
+    }
+
+    /**
+     * @param mixed[] $assets
+     * @return mixed[]
+     */
+    public function render(array $assets): array
+    {
+        $is_footer = isset($assets['retrofit']);
+        unset($assets['retrofit']);
+        $elements = $this->inner->render($assets);
+        if ($is_footer && !empty($this->retrofitFooter)) {
+            $elements = array_merge($elements, $this->retrofitFooter);
+        }
+        return $elements;
+    }
+
+    /**
+     * @param array{
+     *   '#type': string,
+     *   '#tag': string,
+     *   '#value'?: string,
+     *   '#attributes'?: mixed[],
+     * } $element
+     */
+    public function addRetrofitFooter(array $element): void
+    {
+        $this->retrofitFooter[] = $element;
+    }
+}
diff --git a/src/Asset/RetrofitLibraryDiscovery.php b/src/Asset/RetrofitLibraryDiscovery.php
new file mode 100644
index 00000000..33a57cd7
--- /dev/null
+++ b/src/Asset/RetrofitLibraryDiscovery.php
@@ -0,0 +1,106 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Retrofit\Drupal\Asset;
+
+use Drupal\Core\Asset\LibraryDiscoveryInterface;
+
+class RetrofitLibraryDiscovery implements LibraryDiscoveryInterface
+{
+    /**
+     * @var array<mixed[]>
+     */
+    protected array $retrofitLibraries = [];
+
+    public function __construct(
+        private readonly LibraryDiscoveryInterface $inner,
+    ) {
+    }
+
+    /**
+     * @param string $extension
+     * @return array<mixed[]>
+     */
+    public function getLibrariesByExtension($extension): array
+    {
+        return match ($extension) {
+            'retrofit' => $this->retrofitLibraries,
+            default => $this->inner->getLibrariesByExtension($extension),
+        };
+    }
+
+    /**
+     * @param string $extension
+     * @param string $name
+     * @return mixed[]|false
+     */
+    public function getLibraryByName($extension, $name): array|false
+    {
+        return match ($extension) {
+            'retrofit' => $this->retrofitLibraries[$name] ?? false,
+            default => $this->inner->getLibraryByName($extension, $name),
+        };
+    }
+
+    public function clearCachedDefinitions(): void
+    {
+        $this->inner->clearCachedDefinitions();
+    }
+
+    /**
+     * @param array{
+     *   css?: mixed[],
+     *   js?: mixed[],
+     *   requires_jquery?: bool,
+     * } $attachments
+     */
+    public function setRetrofitLibrary(string $key, array $attachments): void
+    {
+        $this->retrofitLibraries[$key]['license'] = [];
+        if (!empty($attachments['js'])) {
+            $this->retrofitLibraries[$key]['dependencies'][] = 'core/drupalSettings';
+            $this->retrofitLibraries[$key]['js'][] = [
+                'data' => 'retrofit',
+                'scope' => 'footer',
+            ];
+            if (!empty($attachments['requires_jquery'])) {
+                $this->retrofitLibraries[$key]['dependencies'][] = 'core/jquery';
+                $this->retrofitLibraries[$key]['dependencies'][] = 'core/once';
+            }
+        }
+        foreach (['css', 'js'] as $type) {
+            foreach ($attachments[$type] ?? [] as $data => $options) {
+                if (!is_array($options)) {
+                    $options = ['data' => $options];
+                }
+                if (!is_numeric($data)) {
+                    $options['data'] = $data;
+                }
+                $options += [
+                    'type' => 'file',
+                    'version' => -1,
+                ];
+                switch ($type) {
+                    case 'css':
+                        $options['weight'] ??= 0;
+                        $options['weight'] += match ($options['group'] ?? CSS_DEFAULT) {
+                            CSS_SYSTEM => CSS_LAYOUT,
+                            CSS_THEME, 100 => CSS_AGGREGATE_THEME,
+                            default => CSS_AGGREGATE_DEFAULT,
+                        };
+                        if (!isset($options['group']) || $options['group'] !== CSS_AGGREGATE_THEME) {
+                            $options['group'] = CSS_AGGREGATE_DEFAULT;
+                        }
+                        break;
+
+                    case 'js':
+                        $options['group'] = JS_LIBRARY;
+                        $options['minified'] ??= false;
+                        break;
+                }
+                $this->retrofitLibraries[$key][$type][] = $options;
+            }
+        }
+    }
+}
diff --git a/src/Provider.php b/src/Provider.php
index e44f09a1..c0392ea0 100644
--- a/src/Provider.php
+++ b/src/Provider.php
@@ -7,6 +7,8 @@
 use Drupal\Core\DependencyInjection\ContainerBuilder;
 use Drupal\Core\DependencyInjection\ServiceProviderBase;
 use Drupal\Core\Template\Loader\FilesystemLoader;
+use Retrofit\Drupal\Asset\RetrofitJsCollectionRenderer;
+use Retrofit\Drupal\Asset\RetrofitLibraryDiscovery;
 use Retrofit\Drupal\Controller\RetrofitTitleResolver;
 use Retrofit\Drupal\Field\FieldTypePluginManager;
 use Retrofit\Drupal\Form\FormBuilder;
@@ -112,11 +114,21 @@ public function register(ContainerBuilder $container)
 
         $container->register(RetrofitHtmlResponseAttachmentsProcessor::class)
             ->setDecoratedService('html_response.attachments_processor')
-            ->addArgument(new Reference(RetrofitHtmlResponseAttachmentsProcessor::class . '.inner'));
+            ->addArgument(new Reference(RetrofitHtmlResponseAttachmentsProcessor::class . '.inner'))
+            ->addArgument(new Reference('asset.js.collection_renderer'))
+            ->setAutowired(true);
 
         $container->register(AttachmentResponseSubscriber::class)
             ->addTag('event_subscriber');
 
+        $container->register(RetrofitLibraryDiscovery::class)
+            ->setDecoratedService('library.discovery')
+            ->setAutowired(true);
+
+        $container->register(RetrofitJsCollectionRenderer::class)
+            ->setDecoratedService('asset.js.collection_renderer')
+            ->setAutowired(true);
+
         $container->setDefinition(
             FieldTypePluginManager::class,
             (new ChildDefinition('plugin.manager.field.field_type'))
diff --git a/src/Render/RetrofitHtmlResponseAttachmentsProcessor.php b/src/Render/RetrofitHtmlResponseAttachmentsProcessor.php
index 9cf34187..73508c44 100644
--- a/src/Render/RetrofitHtmlResponseAttachmentsProcessor.php
+++ b/src/Render/RetrofitHtmlResponseAttachmentsProcessor.php
@@ -4,14 +4,21 @@
 
 namespace Retrofit\Drupal\Render;
 
+use Drupal\Component\Utility\Crypt;
 use Drupal\Component\Utility\NestedArray;
+use Drupal\Core\Asset\AssetCollectionRendererInterface;
+use Drupal\Core\Asset\LibraryDiscoveryInterface;
 use Drupal\Core\Render\AttachmentsInterface;
 use Drupal\Core\Render\AttachmentsResponseProcessorInterface;
+use Retrofit\Drupal\Asset\RetrofitJsCollectionRenderer;
+use Retrofit\Drupal\Asset\RetrofitLibraryDiscovery;
 
 final class RetrofitHtmlResponseAttachmentsProcessor implements AttachmentsResponseProcessorInterface
 {
     public function __construct(
         private readonly AttachmentsResponseProcessorInterface $inner,
+        private readonly AssetCollectionRendererInterface $jsCollectionRenderer,
+        private readonly LibraryDiscoveryInterface $libraryDiscovery,
     ) {
     }
 
@@ -29,19 +36,110 @@ public function processAttachments(AttachmentsInterface $response)
                 }
             }
         }
-        if (isset($attachments['js']) && is_array($attachments['js'])) {
-            foreach ($attachments['js'] as $key => $item) {
-                if (is_array($item) && isset($item['type'], $item['data']) && $item['type'] === 'setting') {
-                    $attachments['drupalSettings'] = NestedArray::mergeDeepArray(
-                        [$attachments['drupalSettings'] ?? [], $item['data']],
-                        true,
+        $retrofit_library = [];
+        if (isset($attachments['css']) && is_array($attachments['css'])) {
+            foreach ($attachments['css'] as $key => $item) {
+                if (is_array($item) && isset($item['type'], $item['data']) && $item['type'] === 'inline') {
+                    $element = [
+                        '#tag' => 'style',
+                        '#value' => $item['data'],
+                        '#weight' => $item['weight'] ?? 0,
+                    ];
+                    unset(
+                        $item['data'],
+                        $item['type'],
+                        $item['basename'],
+                        $item['group'],
+                        $item['every_page'],
+                        $item['weight'],
+                        $item['preprocess'],
+                        $item['browsers'],
                     );
-                    unset($attachments['js'][$key]);
+                    $element['#attributes'] = $item;
+                    $attachments['html_head'][] = [
+                        $element,
+                        "retrofit:$key",
+                    ];
+                    unset($attachments['css'][$key]);
+                }
+            }
+            $retrofit_library['css'] = $attachments['css'];
+            unset($attachments['css']);
+            asort($retrofit_library['css']);
+        }
+        if (isset($attachments['js']) && is_array($attachments['js'])) {
+            $requires_jquery = false;
+            foreach ($attachments['js'] as $key => &$item) {
+                if (is_array($item)) {
+                    $requires_jquery = !empty($item['requires_jquery']) ?: $requires_jquery;
+                    switch ($item['type'] ?? 'file') {
+                        case 'inline':
+                            $element = [
+                                '#tag' => 'script',
+                                '#value' => $item['data'] ?? $key,
+                                '#weight' => $item['weight'] ?? 0,
+                            ];
+                            $scope = $item['scope'] ?? 'footer';
+                            unset(
+                                $item['data'],
+                                $item['type'],
+                                $item['scope'],
+                                $item['group'],
+                                $item['every_page'],
+                                $item['weight'],
+                                $item['requires_jquery'],
+                                $item['cache'],
+                                $item['preprocess'],
+                            );
+                            $element['#attributes'] = $item;
+                            unset($attachments['js'][$key]);
+                            switch ($scope) {
+                                case 'header':
+                                    $attachments['html_head'][] = [
+                                        $element,
+                                        "retrofit:$key",
+                                    ];
+                                    break;
+
+                                default:
+                                    $element['#type'] = 'html_tag';
+                                    assert($this->jsCollectionRenderer instanceof RetrofitJsCollectionRenderer);
+                                    $this->jsCollectionRenderer->addRetrofitFooter($element);
+                                    break;
+                            }
+                            break;
+
+                        case 'setting':
+                            if (isset($item['data'])) {
+                                $attachments['drupalSettings'] = NestedArray::mergeDeepArray(
+                                    [$attachments['drupalSettings'] ?? [], $item['data']],
+                                    true,
+                                );
+                            }
+                            unset($attachments['js'][$key]);
+                            break;
+
+                        default:
+                            $item['attributes']['defer'] = $item['defer'] ?? false;
+                            break;
+                    }
                 }
             }
+            assert($this->jsCollectionRenderer instanceof RetrofitJsCollectionRenderer);
+            $this->jsCollectionRenderer->addRetrofitFooter([
+                '#type' => 'html_tag',
+                '#tag' => 'script',
+                '#value' => 'Drupal.settings = drupalSettings;',
+            ]);
+            $retrofit_library['requires_jquery'] = $requires_jquery;
+            $retrofit_library['js'] = $attachments['js'];
+            unset($attachments['js']);
+            asort($retrofit_library['js']);
         }
-        // @todo log these removals?
-        unset($attachments['css'], $attachments['js']);
+        $name = Crypt::hashBase64(serialize($retrofit_library));
+        assert($this->libraryDiscovery instanceof RetrofitLibraryDiscovery);
+        $this->libraryDiscovery->setRetrofitLibrary($name, $retrofit_library);
+        $attachments['library'][] = "retrofit/$name";
         $response->setAttachments($attachments);
         return $this->inner->processAttachments($response);
     }
diff --git a/src/constants/common.php b/src/constants/common.php
index a2f230f9..8f84e33c 100644
--- a/src/constants/common.php
+++ b/src/constants/common.php
@@ -4,3 +4,5 @@
 
 // In Drupal 10 this has been replaced with CSS_AGGREGATE_DEFAULT.
 const CSS_DEFAULT = 0;
+
+const CSS_SYSTEM = -100;
diff --git a/src/functions/common.php b/src/functions/common.php
index 50ee6da2..956d6df6 100644
--- a/src/functions/common.php
+++ b/src/functions/common.php
@@ -214,34 +214,38 @@ function drupal_add_library(string $module, string $name, ?bool $every_page = nu
  */
 function drupal_add_js(array|string|null $data = null, array|string|null $options = null): array
 {
-    if ($data === null) {
-        return [];
-    }
+
     $attachment_subscriber = \Drupal::getContainer()->get(AttachmentResponseSubscriber::class);
     assert($attachment_subscriber instanceof AttachmentResponseSubscriber);
 
-    if (is_string($options)) {
+    $options ??= [];
+    if (!is_array($options)) {
         $options = ['type' => $options];
-    } elseif ($options === null) {
-        $options = [];
     }
-
-    $type = $options['type'] ?? 'file';
-    switch ($type) {
+    $options += [
+        'type' => 'file',
+        'requires_jquery' => isset($options['type']) && $options['type'] === 'setting',
+        'scope' => 'footer',
+        'cache' => true,
+        'defer' => false,
+        'preprocess' => true,
+        'data' => $data,
+    ];
+    $options['preprocess'] = $options['cache'] ? $options['preprocess'] : false;
+    switch ($options['type']) {
         case 'setting':
             if (is_array($data)) {
                 $attachment_subscriber->addAttachments([
                     'drupalSettings' => $data,
                 ]);
-            } else {
-                // @todo log warning if string? Cannot discern what D7 did.
             }
-
             break;
 
         case 'inline':
             $attachment_subscriber->addAttachments([
-                'js' => $options,
+                'js' => [
+                    $options,
+                ],
             ]);
             break;
 
diff --git a/tests/src/Unit/Render/RetrofitHtmlResponseAttachmentsProcessorTest.php b/tests/src/Unit/Render/RetrofitHtmlResponseAttachmentsProcessorTest.php
index b30c2afc..a9a7573f 100644
--- a/tests/src/Unit/Render/RetrofitHtmlResponseAttachmentsProcessorTest.php
+++ b/tests/src/Unit/Render/RetrofitHtmlResponseAttachmentsProcessorTest.php
@@ -4,9 +4,11 @@
 
 namespace Retrofit\Drupal\Tests\Unit\Render;
 
+use Drupal\Core\Asset\AssetCollectionRendererInterface;
 use Drupal\Core\Render\AttachmentsResponseProcessorInterface;
 use Drupal\Core\Render\HtmlResponse;
 use PHPUnit\Framework\TestCase;
+use Retrofit\Drupal\Asset\RetrofitLibraryDiscovery;
 use Retrofit\Drupal\Render\RetrofitHtmlResponseAttachmentsProcessor;
 
 /**
@@ -29,12 +31,15 @@ public function testProcessAttachments(): void
         $inner->expects(self::once())
             ->method('processAttachments')
             ->with($response);
-        $sut = new RetrofitHtmlResponseAttachmentsProcessor($inner);
+        $jsCollectionRenderer = $this->createMock(AssetCollectionRendererInterface::class);
+        $libraryDiscovery = $this->createMock(RetrofitLibraryDiscovery::class);
+        $sut = new RetrofitHtmlResponseAttachmentsProcessor($inner, $jsCollectionRenderer, $libraryDiscovery);
         $sut->processAttachments($response);
         self::assertEquals(
             [
                 'library' => [
-                    'foo/bar'
+                    'foo/bar',
+                    'retrofit/NXhscRe0440PFpI5dSznEVgmauL25KojD7u4e9aZwOM',
                 ],
             ],
             $response->getAttachments()