From 3e741a9516ccc8b2edb9d002ca054b2be96287fd Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 19:03:26 +0800
Subject: [PATCH 1/9] add env

---
 packages/kit/src/exports/vite/dev/index.js    |   3 +-
 packages/kit/src/exports/vite/index.js        | 273 ++++++++++--------
 .../test/apps/basics/src/service-worker.js    |   7 +
 .../test/apps/options-2/src/service-worker.js |  12 +-
 packages/kit/test/apps/options-2/test/test.js |  13 -
 5 files changed, 164 insertions(+), 144 deletions(-)

diff --git a/packages/kit/src/exports/vite/dev/index.js b/packages/kit/src/exports/vite/dev/index.js
index 52923f56e880..0722a4c56c63 100644
--- a/packages/kit/src/exports/vite/dev/index.js
+++ b/packages/kit/src/exports/vite/dev/index.js
@@ -475,10 +475,11 @@ export async function dev(vite, vite_config, svelte_config, get_remotes, root) {
 					const resolved = resolve_entry(svelte_config.kit.files.serviceWorker);
 
 					if (resolved) {
+						const transformed = await vite.environments.serviceWorker.transformRequest(resolved);
 						res.writeHead(200, {
 							'content-type': 'application/javascript'
 						});
-						res.end(`import '${svelte_config.kit.paths.base}${to_fs(resolved)}';`);
+						res.end(transformed?.code);
 					} else {
 						res.writeHead(404);
 						res.end('not found');
diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 17cc04de9110..f3b93c143bee 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -4,6 +4,7 @@ import process from 'node:process';
 import { styleText } from 'node:util';
 
 import { exactRegex, prefixRegex } from 'rolldown/filter';
+import { createFetchableDevEnvironment, normalizePath } from 'vite';
 
 import { copy, mkdirp, posixify, read, resolve_entry, rimraf } from '../../utils/filesystem.js';
 import { create_static_module, create_dynamic_module } from '../../core/env.js';
@@ -260,11 +261,6 @@ function kit({ svelte_config }) {
 	/** @type {import('vite').UserConfig} */
 	let initial_config;
 
-	/** @type {string | null} */
-	let service_worker_entry_file;
-	/** @type {import('node:path').ParsedPath} */
-	let parsed_service_worker;
-
 	/** @type {string} */
 	let normalized_cwd;
 	/** @type {string} */
@@ -285,10 +281,6 @@ function kit({ svelte_config }) {
 	const plugin_setup = {
 		name: 'vite-plugin-sveltekit-setup',
 
-		applyToEnvironment(environment) {
-			return environment.name !== 'serviceWorker';
-		},
-
 		// TODO: add `order: pre` to avoid false-positive warnings of overridden config options set by Vitest
 		/**
 		 * Build the SvelteKit-provided Vite config to be merged with the user's vite.config.js file.
@@ -306,9 +298,6 @@ function kit({ svelte_config }) {
 
 			env = get_env(kit.env, vite_config_env.mode);
 
-			service_worker_entry_file = resolve_entry(kit.files.serviceWorker);
-			parsed_service_worker = path.parse(kit.files.serviceWorker);
-
 			vite = await import_peer('vite', root);
 
 			normalized_cwd = vite.normalizePath(root);
@@ -473,44 +462,25 @@ function kit({ svelte_config }) {
 			return environment.name !== 'serviceWorker';
 		},
 
-		resolveId(id, importer) {
-			if (id === '__sveltekit/manifest') {
-				return `${kit.outDir}/generated/client-optimized/app.js`;
-			}
-
-			// If importing from a service-worker, only allow $service-worker & $env/static/public, but none of the other virtual modules.
-			// This check won't catch transitive imports, but it will warn when the import comes from a service-worker directly.
-			// Transitive imports will be caught during the build.
-			// TODO move this logic to plugin_guard. add a filter to this resolveId when doing so
-			if (importer) {
-				const parsed_importer = path.parse(importer);
-
-				const importer_is_service_worker =
-					parsed_importer.dir === parsed_service_worker.dir &&
-					parsed_importer.name === parsed_service_worker.name;
-
-				if (importer_is_service_worker && id !== '$service-worker' && id !== '$env/static/public') {
-					throw new Error(
-						`Cannot import ${normalize_id(
-							id,
-							normalized_lib,
-							normalized_cwd
-						)} into service-worker code. Only the modules $service-worker and $env/static/public are available in service workers.`
-					);
+		resolveId: {
+			filter: {
+				id: [prefixRegex('$env/'), exactRegex('$service-worker'), prefixRegex('__sveltekit/')]
+			},
+			handler(id) {
+				// treat $env/static/[public|private] as virtual
+				if (id.startsWith('$env/') || id === '$service-worker') {
+					// ids with :$ don't work with reverse proxies like nginx
+					return `\0virtual:${id.substring(1)}`;
 				}
-			}
 
-			// treat $env/static/[public|private] as virtual
-			if (id.startsWith('$env/') || id === '$service-worker') {
-				// ids with :$ don't work with reverse proxies like nginx
-				return `\0virtual:${id.substring(1)}`;
-			}
+				if (id === '__sveltekit/manifest') {
+					return `${kit.outDir}/generated/client-optimized/app.js`;
+				}
 
-			if (id === '__sveltekit/remote') {
-				return `${runtime_directory}/client/remote-functions/index.js`;
-			}
+				if (id === '__sveltekit/remote') {
+					return `${runtime_directory}/client/remote-functions/index.js`;
+				}
 
-			if (id.startsWith('__sveltekit/')) {
 				return `\0virtual:${id}`;
 			}
 		},
@@ -907,11 +877,8 @@ function kit({ svelte_config }) {
 	let client_manifest;
 	/** @type {import('types').Prerendered} */
 	let prerendered;
-
-	/** @type {Set<string>} */
-	let build;
-	/** @type {string} */
-	let service_worker_code;
+	/** @type {string | null} */
+	let service_worker_entry_file;
 
 	/**
 	 * Creates the service worker virtual modules
@@ -920,72 +887,152 @@ function kit({ svelte_config }) {
 	const plugin_service_worker = {
 		name: 'vite-plugin-sveltekit-service-worker',
 
+		config(config) {
+			service_worker_entry_file = resolve_entry(kit.files.serviceWorker);
+
+			if (!service_worker_entry_file) return;
+
+			if (kit.paths.assets) {
+				throw new Error('Cannot use service worker alongside config.kit.paths.assets');
+			}
+
+			// TODO: in the future we can use unbundled service workers as the default
+			// it became baseline in January 2026 https://caniuse.com/wf-js-modules-service-workers
+
+			const conditions = ['worker', 'browser', 'production|development'];
+
+			/** @type {import('vite').UserConfig} */
+			const new_config = {
+				environments: {
+					serviceWorker: {
+						consumer: 'client',
+						resolve: {
+							conditions
+							// TODO: bundle the worker in development once noExternal is supported for client environments
+							// noExternal: kit.serviceWorker.type === 'module' ? undefined : true
+						},
+						optimizeDeps: {
+							// Note: ssr pre-bundling is opt-in and we need to enable it by setting `noDiscovery` to false
+							// noDiscovery: false,
+							// Workaround for https://github.com/vitejs/vite/issues/20867
+							// Longer term solution is to use full-bundle mode rather than `optimizeDeps`
+							// ignoreOutdatedRequests: true,
+							entries: normalizePath(kit.files.serviceWorker),
+							rolldownOptions: {
+								platform: 'neutral',
+								resolve: {
+									conditionNames: conditions
+								}
+							}
+						},
+						dev: {
+							createEnvironment(name, config) {
+								return createFetchableDevEnvironment(name, config, {
+									hot: false,
+									handleRequest() {
+										throw new Error(
+											'This should never happen. The service worker environment does not handle requests directly'
+										);
+									}
+								});
+							}
+						},
+						build: {
+							modulePreload: false,
+							rolldownOptions: {
+								input: {
+									'service-worker': service_worker_entry_file
+								},
+								output: {
+									entryFileNames: 'service-worker.js',
+									assetFileNames: `${kit.appDir}/immutable/assets/[name].[hash][extname]`,
+									codeSplitting: false
+								}
+							},
+							outDir: `${out}/client`,
+							minify: initial_config.build?.minify
+						}
+					}
+				}
+			};
+
+			warn_overridden_config(config, new_config);
+
+			return new_config;
+		},
+
 		applyToEnvironment(environment) {
 			return environment.name === 'serviceWorker';
 		},
 
-		resolveId(id) {
-			if (id.startsWith('$env/') || id.startsWith('$app/') || id === '$service-worker') {
+		resolveId: {
+			order: 'pre',
+			filter: {
+				id: [prefixRegex('$env/'), prefixRegex('$app/'), exactRegex('$service-worker')]
+			},
+			handler(id) {
 				// ids with :$ don't work with reverse proxies like nginx
 				return `\0virtual:${id.substring(1)}`;
 			}
 		},
 
-		load(id) {
-			if (!build) {
-				build = new Set();
-				for (const key in client_manifest) {
-					const { file, css = [], assets = [] } = client_manifest[key];
-					build.add(file);
-					css.forEach((file) => build.add(file));
-					assets.forEach((file) => build.add(file));
-				}
+		load: {
+			filter: {
+				id: [/^(?!\\0virtual:).*/, exactRegex(env_static_public), exactRegex(service_worker)]
+			},
+			handler(id) {
+				if (id === service_worker_entry_file) return;
+
+				if (id === service_worker) {
+					const build = new Set();
+					for (const key in client_manifest) {
+						const { file, css = [], assets = [] } = client_manifest[key];
+						build.add(file);
+						css.forEach((file) => build.add(file));
+						assets.forEach((file) => build.add(file));
+					}
 
-				// in a service worker, `location` is the location of the service worker itself,
-				// which is guaranteed to be `<base>/service-worker.js`
-				const base = "location.pathname.split('/').slice(0, -1).join('/')";
+					// in a service worker, `location` is the location of the service worker itself,
+					// which is guaranteed to be `<base>/service-worker.js`
+					const base = "location.pathname.split('/').slice(0, -1).join('/')";
 
-				service_worker_code = dedent`
-					export const base = /*@__PURE__*/ ${base};
+					// in dev, this doesn't exist, so we need to create it
+					manifest_data ??= sync.all(svelte_config, vite_config_env.mode, root).manifest_data;
 
-					export const build = [
-						${Array.from(build)
-							.map((file) => `base + ${s(`/${file}`)}`)
-							.join(',\n')}
-					];
+					return dedent`
+						export const base = /*@__PURE__*/ ${base};
 
-					export const files = [
-						${manifest_data.assets
-							.filter((asset) => kit.serviceWorker.files(asset.file))
-							.map((asset) => `base + ${s(`/${asset.file}`)}`)
-							.join(',\n')}
-					];
+						export const build = [
+							${Array.from(build)
+								.map((file) => `base + ${s(`/${file}`)}`)
+								.join(',\n')}
+						];
 
-					export const prerendered = [
-						${prerendered.paths.map((path) => `base + ${s(path.replace(kit.paths.base, ''))}`).join(',\n')}
-					];
+						export const files = [
+							${manifest_data.assets
+								.filter((asset) => kit.serviceWorker.files(asset.file))
+								.map((asset) => `base + ${s(`/${asset.file}`)}`)
+								.join(',\n')}
+						];
 
-					export const version = ${s(kit.version.name)};
-				`;
-			}
+						export const prerendered = [
+							${prerendered?.paths.map((path) => `base + ${s(path.replace(kit.paths.base, ''))}`).join(',\n')}
+						];
 
-			if (!id.startsWith('\0virtual:')) return;
+						export const version = ${s(kit.version.name)};
+					`;
+				}
 
-			if (id === service_worker) {
-				return service_worker_code;
-			}
+				if (id === env_static_public) {
+					return create_static_module('$env/static/public', env.public);
+				}
 
-			if (id === env_static_public) {
-				return create_static_module('$env/static/public', env.public);
+				const relative = normalize_id(id, normalized_lib, normalized_cwd);
+				const stripped = strip_virtual_prefix(relative);
+				throw new Error(
+					`Cannot import ${stripped} into service-worker code. Only the modules $service-worker and $env/static/public are available in service workers.`
+				);
 			}
-
-			const normalized_cwd = vite.normalizePath(vite_config.root);
-			const normalized_lib = vite.normalizePath(kit.files.lib);
-			const relative = normalize_id(id, normalized_lib, normalized_cwd);
-			const stripped = strip_virtual_prefix(relative);
-			throw new Error(
-				`Cannot import ${stripped} into service-worker code. Only the modules $service-worker and $env/static/public are available in service workers.`
-			);
 		}
 	};
 
@@ -1224,29 +1271,6 @@ function kit({ svelte_config }) {
 					},
 					publicDir: kit.files.assets
 				};
-
-				if (service_worker_entry_file) {
-					/** @type {Record<string, import('vite').EnvironmentOptions>} */ (
-						new_config.environments
-					).serviceWorker = {
-						build: {
-							modulePreload: false,
-							rolldownOptions: {
-								input: {
-									'service-worker': service_worker_entry_file
-								},
-								output: {
-									entryFileNames: 'service-worker.js',
-									assetFileNames: `${kit.appDir}/immutable/assets/[name].[hash][extname]`,
-									codeSplitting: false
-								}
-							},
-							outDir: `${out}/client`,
-							minify: initial_config.build?.minify
-						},
-						consumer: 'client'
-					};
-				}
 			} else {
 				new_config = {
 					appType: 'custom',
@@ -1577,12 +1601,7 @@ function kit({ svelte_config }) {
 			);
 
 			if (service_worker_entry_file) {
-				if (kit.paths.assets) {
-					throw new Error('Cannot use service worker alongside config.kit.paths.assets');
-				}
-
-				log.info('Building service worker');
-
+				// mirror client settings that we can't set in the environment config earlier
 				builder.environments.serviceWorker.config.define =
 					builder.environments.client.config.define;
 				builder.environments.serviceWorker.config.resolve.alias = [
diff --git a/packages/kit/test/apps/basics/src/service-worker.js b/packages/kit/test/apps/basics/src/service-worker.js
index fc3dbc27600f..52dda00c86f8 100644
--- a/packages/kit/test/apps/basics/src/service-worker.js
+++ b/packages/kit/test/apps/basics/src/service-worker.js
@@ -1,3 +1,10 @@
+/// <reference no-default-lib="true"/>
+/// <reference lib="esnext" />
+/// <reference lib="webworker" />
+
+/// <reference types="@sveltejs/kit" />
+/// <reference types="../.svelte-kit/ambient.d.ts" />
+
 import { build, version } from '$service-worker';
 import { PUBLIC_STATIC } from '$env/static/public';
 
diff --git a/packages/kit/test/apps/options-2/src/service-worker.js b/packages/kit/test/apps/options-2/src/service-worker.js
index 5d2346ffc333..84bce78f173f 100644
--- a/packages/kit/test/apps/options-2/src/service-worker.js
+++ b/packages/kit/test/apps/options-2/src/service-worker.js
@@ -1,6 +1,15 @@
+/// <reference no-default-lib="true"/>
+/// <reference lib="esnext" />
+/// <reference lib="webworker" />
+
+/// <reference types="@sveltejs/kit" />
+
 import { base, build, version } from '$service-worker';
 import src from './image.jpg?url';
 
+// This gives `self` the correct types
+const self = /** @type {ServiceWorkerGlobalScope} */ (/** @type {unknown} */ (globalThis.self));
+
 //@ts-ignore
 self.base = base;
 //@ts-ignore
@@ -11,12 +20,10 @@ self.image_src = src;
 const name = `cache-${version}`;
 
 self.addEventListener('install', (event) => {
-	// @ts-expect-error
 	event.waitUntil(caches.open(name).then((cache) => cache.addAll(build)));
 });
 
 self.addEventListener('activate', (event) => {
-	// @ts-expect-error
 	event.waitUntil(
 		caches.keys().then(async (keys) => {
 			for (const key of keys) {
@@ -27,7 +34,6 @@ self.addEventListener('activate', (event) => {
 });
 
 self.addEventListener('fetch', (event) => {
-	// @ts-expect-error
 	const { request } = event;
 
 	if (request.method !== 'GET' || request.headers.has('range')) return;
diff --git a/packages/kit/test/apps/options-2/test/test.js b/packages/kit/test/apps/options-2/test/test.js
index 02d78b60e359..c89dd18f4adf 100644
--- a/packages/kit/test/apps/options-2/test/test.js
+++ b/packages/kit/test/apps/options-2/test/test.js
@@ -1,4 +1,3 @@
-import path from 'node:path';
 import process from 'node:process';
 import { expect } from '@playwright/test';
 import { test } from '../../../utils.js';
@@ -123,18 +122,6 @@ test.describe('trailing slash', () => {
 });
 
 test.describe('Service worker', () => {
-	if (process.env.DEV) {
-		test('import proxy /basepath/service-worker.js', async ({ request }) => {
-			const response = await request.get('/basepath/service-worker.js');
-			const content = await response.text();
-			expect(content).toEqual(
-				`import '${path.join('/basepath', '/@fs', import.meta.dirname, '../src/service-worker.js')}';`
-			);
-		});
-
-		return;
-	}
-
 	test('build /basepath/service-worker.js', async ({ baseURL, request }) => {
 		const response = await request.get('/basepath/service-worker.js');
 		const content = await response.text();

From cff828a94fe3629f13d09b288f9933e0c271876b Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 19:03:30 +0800
Subject: [PATCH 2/9] fix types

---
 packages/kit/src/exports/public.d.ts | 4 ++--
 packages/kit/types/index.d.ts        | 4 ++--
 2 files changed, 4 insertions(+), 4 deletions(-)

diff --git a/packages/kit/src/exports/public.d.ts b/packages/kit/src/exports/public.d.ts
index 8124d09ebd55..7dd0b07e593d 100644
--- a/packages/kit/src/exports/public.d.ts
+++ b/packages/kit/src/exports/public.d.ts
@@ -834,9 +834,9 @@ export interface KitConfig {
 				 * Whether to automatically register the service worker, if it exists.
 				 * @default true
 				 */
-				register: true;
+				register?: true;
 				/**
-				 * Options for serviceWorker.register("...", options);
+				 * Options passed to the automatic service worker registration `serviceWorker.register("...", options);`
 				 */
 				options?: RegistrationOptions;
 		  }
diff --git a/packages/kit/types/index.d.ts b/packages/kit/types/index.d.ts
index 3ddb59f94727..c2e8b180a19e 100644
--- a/packages/kit/types/index.d.ts
+++ b/packages/kit/types/index.d.ts
@@ -808,9 +808,9 @@ declare module '@sveltejs/kit' {
 					 * Whether to automatically register the service worker, if it exists.
 					 * @default true
 					 */
-					register: true;
+					register?: true;
 					/**
-					 * Options for serviceWorker.register("...", options);
+					 * Options passed to the automatic service worker registration `serviceWorker.register("...", options);`
 					 */
 					options?: RegistrationOptions;
 			  }

From 48877f2dad23429f22445217cc5b1fe856854948 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 19:12:56 +0800
Subject: [PATCH 3/9] comment

---
 packages/kit/src/exports/vite/index.js         | 3 ---
 packages/kit/src/runtime/server/page/render.js | 2 ++
 2 files changed, 2 insertions(+), 3 deletions(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index f3b93c143bee..544f3009bfc7 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -896,9 +896,6 @@ function kit({ svelte_config }) {
 				throw new Error('Cannot use service worker alongside config.kit.paths.assets');
 			}
 
-			// TODO: in the future we can use unbundled service workers as the default
-			// it became baseline in January 2026 https://caniuse.com/wf-js-modules-service-workers
-
 			const conditions = ['worker', 'browser', 'production|development'];
 
 			/** @type {import('vite').UserConfig} */
diff --git a/packages/kit/src/runtime/server/page/render.js b/packages/kit/src/runtime/server/page/render.js
index 104cc1de5b1b..3ae1607be64e 100644
--- a/packages/kit/src/runtime/server/page/render.js
+++ b/packages/kit/src/runtime/server/page/render.js
@@ -596,6 +596,8 @@ export async function render_response({
 		}
 
 		if (options.service_worker) {
+			// TODO: in the future we could register service workers as a module by default
+			// it became baseline in January 2026 https://caniuse.com/wf-js-modules-service-workers
 			let opts = DEV ? ", { type: 'module' }" : '';
 			if (options.service_worker_options != null) {
 				const service_worker_options = { ...options.service_worker_options };

From 93e7a618baf5c1a99cb5488112ca9834480069b6 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 19:17:41 +0800
Subject: [PATCH 4/9] don't error on handling service worker entry file

---
 packages/kit/src/exports/vite/index.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 544f3009bfc7..e841b9a5f76b 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -978,7 +978,7 @@ function kit({ svelte_config }) {
 				id: [/^(?!\\0virtual:).*/, exactRegex(env_static_public), exactRegex(service_worker)]
 			},
 			handler(id) {
-				if (id === service_worker_entry_file) return;
+				if (id === kit.files.serviceWorker || id === service_worker_entry_file) return;
 
 				if (id === service_worker) {
 					const build = new Set();

From 24f7bf6d0b48ff1ad63313b3bf6570c417ae9870 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 19:41:24 +0800
Subject: [PATCH 5/9] Apply suggestion from @teemingc

---
 packages/kit/src/exports/vite/index.js | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index e841b9a5f76b..f70a8a1741fd 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -975,7 +975,7 @@ function kit({ svelte_config }) {
 
 		load: {
 			filter: {
-				id: [/^(?!\\0virtual:).*/, exactRegex(env_static_public), exactRegex(service_worker)]
+				id: [/^\\0virtual:/, exactRegex(env_static_public), exactRegex(service_worker)]
 			},
 			handler(id) {
 				if (id === kit.files.serviceWorker || id === service_worker_entry_file) return;

From 169f840b0e03fd57c92b42ac6abf12c2742a7dad Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 21:30:54 +0800
Subject: [PATCH 6/9] run server guard for service worker too

---
 packages/kit/src/exports/vite/index.js | 4 ----
 1 file changed, 4 deletions(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index f70a8a1741fd..c87f646ac210 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -584,10 +584,6 @@ function kit({ svelte_config }) {
 		// are added to the module graph
 		enforce: 'pre',
 
-		applyToEnvironment(environment) {
-			return environment.name !== 'serviceWorker';
-		},
-
 		resolveId: {
 			// TODO: use composable filter API here when supported:
 			// https://github.com/vitejs/rolldown-vite/issues/605

From 1a5a35ab1fd1634c2cc06abcda240decb9436db9 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 21:45:35 +0800
Subject: [PATCH 7/9] fix build

---
 packages/kit/src/exports/vite/index.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index c87f646ac210..8a67bdd6deaf 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -943,7 +943,9 @@ function kit({ svelte_config }) {
 								}
 							},
 							outDir: `${out}/client`,
-							minify: initial_config.build?.minify
+							minify: initial_config.build?.minify,
+							// avoid overwriting the client build Vite manifest
+							manifest: '.vite/service-worker-manifest.json'
 						}
 					}
 				}
@@ -959,7 +961,6 @@ function kit({ svelte_config }) {
 		},
 
 		resolveId: {
-			order: 'pre',
 			filter: {
 				id: [prefixRegex('$env/'), prefixRegex('$app/'), exactRegex('$service-worker')]
 			},

From 56d928f3a9d76151e4dfab52597b07cf74fc6175 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Sun, 29 Mar 2026 22:13:12 +0800
Subject: [PATCH 8/9] real fix

---
 packages/kit/src/exports/vite/index.js | 13 +++++++++----
 1 file changed, 9 insertions(+), 4 deletions(-)

diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 8a67bdd6deaf..5ef35632a6c3 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -464,11 +464,11 @@ function kit({ svelte_config }) {
 
 		resolveId: {
 			filter: {
-				id: [prefixRegex('$env/'), exactRegex('$service-worker'), prefixRegex('__sveltekit/')]
+				id: [prefixRegex('$env/'), prefixRegex('__sveltekit/')]
 			},
 			handler(id) {
 				// treat $env/static/[public|private] as virtual
-				if (id.startsWith('$env/') || id === '$service-worker') {
+				if (id.startsWith('$env/')) {
 					// ids with :$ don't work with reverse proxies like nginx
 					return `\0virtual:${id.substring(1)}`;
 				}
@@ -622,7 +622,12 @@ function kit({ svelte_config }) {
 				]
 			},
 			handler(id) {
-				if (this.environment.config.consumer !== 'client') return;
+				if (
+					this.environment.config.consumer !== 'client' ||
+					(this.environment.name === 'serviceWorker' && id === env_dynamic_private)
+				) {
+					return;
+				}
 
 				// skip .server.js files outside the cwd or in node_modules, as the filename might not mean 'server-only module' in this context
 				const is_internal =
@@ -972,7 +977,7 @@ function kit({ svelte_config }) {
 
 		load: {
 			filter: {
-				id: [/^\\0virtual:/, exactRegex(env_static_public), exactRegex(service_worker)]
+				id: [/^\0virtual:/, exactRegex(env_static_public), exactRegex(service_worker)]
 			},
 			handler(id) {
 				if (id === kit.files.serviceWorker || id === service_worker_entry_file) return;

From 97baddafd9966f1e3325cba5d69bb62f6634c589 Mon Sep 17 00:00:00 2001
From: Tee Ming <chewteeming01@gmail.com>
Date: Tue, 31 Mar 2026 10:33:49 +0800
Subject: [PATCH 9/9] wip

---
 .../src/exports/vite/build/service_worker.js  |  32 +++++
 packages/kit/src/exports/vite/dev/index.js    |  17 ++-
 packages/kit/src/exports/vite/index.js        | 109 +++++-------------
 packages/kit/test/apps/options-2/.gitignore   |   1 +
 .../test/apps/options-2/src/service-worker.js |   6 +-
 packages/kit/test/apps/options-2/test/test.js |  46 +++++---
 6 files changed, 109 insertions(+), 102 deletions(-)
 create mode 100644 packages/kit/src/exports/vite/build/service_worker.js
 create mode 100644 packages/kit/test/apps/options-2/.gitignore

diff --git a/packages/kit/src/exports/vite/build/service_worker.js b/packages/kit/src/exports/vite/build/service_worker.js
new file mode 100644
index 000000000000..3d0691b87fe4
--- /dev/null
+++ b/packages/kit/src/exports/vite/build/service_worker.js
@@ -0,0 +1,32 @@
+/**
+ * @param {import("vite").ViteBuilder} builder
+ * @param {import("vite").Alias[]} config_aliases
+ * @returns {Promise<string>}
+ */
+export async function build_service_worker(builder, config_aliases) {
+	// mirror client settings that we couldn't set per environment in the config hook
+	builder.environments.serviceWorker.config.define = builder.environments.client.config.define;
+	builder.environments.serviceWorker.config.resolve.alias = [...config_aliases];
+
+	// we have to overwrite this because it can't be configured per environment in the config hook
+	builder.environments.serviceWorker.config.experimental.renderBuiltUrl = (filename) => {
+		return {
+			runtime: `new URL(${JSON.stringify(filename)}, location.href).pathname`
+		};
+	};
+
+	// TODO: use Vite's dev full-bundle mode when it's out
+	const build = /** @type {import('vite').Rolldown.RolldownOutput} */ (
+		await builder.build(builder.environments.serviceWorker)
+	);
+
+	const chunk = build.output.find(
+		(chunk) => chunk.type === 'chunk' && chunk.fileName === 'service-worker.js'
+	);
+
+	if (chunk?.type !== 'chunk') {
+		throw new Error('Failed to find the service-worker chunk');
+	}
+
+	return chunk.code;
+}
diff --git a/packages/kit/src/exports/vite/dev/index.js b/packages/kit/src/exports/vite/dev/index.js
index 0722a4c56c63..043ad72d2eb1 100644
--- a/packages/kit/src/exports/vite/dev/index.js
+++ b/packages/kit/src/exports/vite/dev/index.js
@@ -4,7 +4,7 @@ import { URL } from 'node:url';
 import { AsyncLocalStorage } from 'node:async_hooks';
 import { styleText } from 'node:util';
 import sirv from 'sirv';
-import { isCSSRequest, loadEnv, buildErrorMessage } from 'vite';
+import { isCSSRequest, loadEnv, buildErrorMessage, createBuilder } from 'vite';
 import { createReadableStream, getRequest, setResponse } from '../../../exports/node/index.js';
 import { coalesce_to_error } from '../../../utils/error.js';
 import { from_fs, posixify, resolve_entry, to_fs } from '../../../utils/filesystem.js';
@@ -17,6 +17,7 @@ import { not_found } from '../utils.js';
 import { SCHEME } from '../../../utils/url.js';
 import { check_feature } from '../../../utils/features.js';
 import { escape_html } from '../../../utils/escape.js';
+import { build_service_worker } from '../build/service_worker.js';
 
 // vite-specifc queries that we should skip handling for css urls
 const vite_css_query_regex = /(?:\?|&)(?:raw|url|inline)(?:&|$)/;
@@ -27,9 +28,10 @@ const vite_css_query_regex = /(?:\?|&)(?:raw|url|inline)(?:&|$)/;
  * @param {import('types').ValidatedConfig} svelte_config
  * @param {() => Array<{ hash: string, file: string }>} get_remotes
  * @param {string} root The project root directory
+ * @param {import('vite').Alias[]} config_aliases
  * @return {Promise<Promise<() => void>>}
  */
-export async function dev(vite, vite_config, svelte_config, get_remotes, root) {
+export async function dev(vite, vite_config, svelte_config, get_remotes, root, config_aliases) {
 	const async_local_storage = new AsyncLocalStorage();
 
 	globalThis.__SVELTEKIT_TRACK__ = (label) => {
@@ -432,6 +434,13 @@ export async function dev(vite, vite_config, svelte_config, get_remotes, root) {
 	const env = loadEnv(vite_config.mode, svelte_config.kit.env.dir, '');
 	const emulator = await svelte_config.kit.adapter?.emulate?.();
 
+	const builder = await createBuilder({
+		build: {
+			write: false,
+			watch: {}
+		}
+	});
+
 	return () => {
 		const serve_static_middleware = vite.middlewares.stack.find(
 			(middleware) =>
@@ -475,11 +484,11 @@ export async function dev(vite, vite_config, svelte_config, get_remotes, root) {
 					const resolved = resolve_entry(svelte_config.kit.files.serviceWorker);
 
 					if (resolved) {
-						const transformed = await vite.environments.serviceWorker.transformRequest(resolved);
+						const service_worker_code = await build_service_worker(builder, config_aliases);
 						res.writeHead(200, {
 							'content-type': 'application/javascript'
 						});
-						res.end(transformed?.code);
+						res.end(service_worker_code);
 					} else {
 						res.writeHead(404);
 						res.end('not found');
diff --git a/packages/kit/src/exports/vite/index.js b/packages/kit/src/exports/vite/index.js
index 5ef35632a6c3..e82e6ef971dc 100644
--- a/packages/kit/src/exports/vite/index.js
+++ b/packages/kit/src/exports/vite/index.js
@@ -4,12 +4,10 @@ import process from 'node:process';
 import { styleText } from 'node:util';
 
 import { exactRegex, prefixRegex } from 'rolldown/filter';
-import { createFetchableDevEnvironment, normalizePath } from 'vite';
 
 import { copy, mkdirp, posixify, read, resolve_entry, rimraf } from '../../utils/filesystem.js';
 import { create_static_module, create_dynamic_module } from '../../core/env.js';
 import * as sync from '../../core/sync/sync.js';
-import { create_assets } from '../../core/sync/create_manifest_data/index.js';
 import { runtime_directory, logger } from '../../core/utils.js';
 import { generate_manifest } from '../../core/generate_manifest/index.js';
 import { build_server_nodes } from './build/build_server.js';
@@ -44,6 +42,7 @@ import { import_peer } from '../../utils/import.js';
 import { compact } from '../../utils/array.js';
 import { should_ignore, has_children } from './static_analysis/utils.js';
 import { load_config } from '../../core/config/index.js';
+import { build_service_worker } from './build/service_worker.js';
 
 const cwd = process.cwd();
 
@@ -277,6 +276,9 @@ function kit({ svelte_config }) {
 	const sourcemapIgnoreList = /** @param {string} relative_path */ (relative_path) =>
 		relative_path.includes('node_modules') || relative_path.includes(kit.outDir);
 
+	/** @type {import('vite').Alias[]} The user's aliases set in svelte.config.js */
+	let config_aliases;
+
 	/** @type {import('vite').Plugin} */
 	const plugin_setup = {
 		name: 'vite-plugin-sveltekit-setup',
@@ -320,6 +322,8 @@ function kit({ svelte_config }) {
 
 			const generated = path.posix.join(kit.outDir, 'generated');
 
+			config_aliases = get_config_aliases(kit, root);
+
 			// dev and preview config can be shared
 			/** @type {import('vite').UserConfig} */
 			const new_config = {
@@ -327,7 +331,7 @@ function kit({ svelte_config }) {
 					alias: [
 						{ find: '__SERVER__', replacement: `${generated}/server` },
 						{ find: '$app', replacement: `${runtime_directory}/app` },
-						...get_config_aliases(kit, root)
+						...config_aliases
 					]
 				},
 				server: {
@@ -464,11 +468,11 @@ function kit({ svelte_config }) {
 
 		resolveId: {
 			filter: {
-				id: [prefixRegex('$env/'), prefixRegex('__sveltekit/')]
+				id: [prefixRegex('$env/'), prefixRegex('__sveltekit/'), exactRegex(service_worker)]
 			},
 			handler(id) {
 				// treat $env/static/[public|private] as virtual
-				if (id.startsWith('$env/')) {
+				if (id.startsWith('$env/') || id === service_worker) {
 					// ids with :$ don't work with reverse proxies like nginx
 					return `\0virtual:${id.substring(1)}`;
 				}
@@ -528,7 +532,7 @@ function kit({ svelte_config }) {
 					}
 
 					case service_worker:
-						return create_service_worker_module(svelte_config);
+						throw new Error('$service-worker can only be imported inside a service worker');
 
 					case sveltekit_environment: {
 						const { version } = svelte_config.kit;
@@ -874,8 +878,8 @@ function kit({ svelte_config }) {
 		}
 	};
 
-	/** @type {import('vite').Manifest} */
-	let client_manifest;
+	/** @type {import('vite').Manifest} Only available when the client build begins */
+	let vite_client_manifest;
 	/** @type {import('types').Prerendered} */
 	let prerendered;
 	/** @type {string | null} */
@@ -904,40 +908,13 @@ function kit({ svelte_config }) {
 				environments: {
 					serviceWorker: {
 						consumer: 'client',
-						resolve: {
-							conditions
-							// TODO: bundle the worker in development once noExternal is supported for client environments
-							// noExternal: kit.serviceWorker.type === 'module' ? undefined : true
-						},
-						optimizeDeps: {
-							// Note: ssr pre-bundling is opt-in and we need to enable it by setting `noDiscovery` to false
-							// noDiscovery: false,
-							// Workaround for https://github.com/vitejs/vite/issues/20867
-							// Longer term solution is to use full-bundle mode rather than `optimizeDeps`
-							// ignoreOutdatedRequests: true,
-							entries: normalizePath(kit.files.serviceWorker),
-							rolldownOptions: {
-								platform: 'neutral',
-								resolve: {
-									conditionNames: conditions
-								}
-							}
-						},
-						dev: {
-							createEnvironment(name, config) {
-								return createFetchableDevEnvironment(name, config, {
-									hot: false,
-									handleRequest() {
-										throw new Error(
-											'This should never happen. The service worker environment does not handle requests directly'
-										);
-									}
-								});
-							}
-						},
 						build: {
 							modulePreload: false,
 							rolldownOptions: {
+								platform: 'browser',
+								resolve: {
+									conditionNames: conditions
+								},
 								input: {
 									'service-worker': service_worker_entry_file
 								},
@@ -977,15 +954,15 @@ function kit({ svelte_config }) {
 
 		load: {
 			filter: {
-				id: [/^\0virtual:/, exactRegex(env_static_public), exactRegex(service_worker)]
+				id: [/^\0virtual:/, exactRegex(env_static_public)]
 			},
 			handler(id) {
 				if (id === kit.files.serviceWorker || id === service_worker_entry_file) return;
 
 				if (id === service_worker) {
 					const build = new Set();
-					for (const key in client_manifest) {
-						const { file, css = [], assets = [] } = client_manifest[key];
+					for (const key in vite_client_manifest) {
+						const { file, css = [], assets = [] } = vite_client_manifest[key];
 						build.add(file);
 						css.forEach((file) => build.add(file));
 						assets.forEach((file) => build.add(file));
@@ -1297,7 +1274,7 @@ function kit({ svelte_config }) {
 		 * @see https://vitejs.dev/guide/api-plugin.html#configureserver
 		 */
 		async configureServer(vite) {
-			return await dev(vite, vite_config, svelte_config, () => remotes, root);
+			return await dev(vite, vite_config, svelte_config, () => remotes, root, config_aliases);
 		},
 
 		/**
@@ -1457,14 +1434,19 @@ function kit({ svelte_config }) {
 			}
 
 			/** @type {import('vite').Manifest} */
-			client_manifest = JSON.parse(read(`${out}/client/.vite/manifest.json`));
+			vite_client_manifest = JSON.parse(read(`${out}/client/.vite/manifest.json`));
 
 			/**
 			 * @param {string} entry
 			 * @param {boolean} [add_dynamic_css]
 			 */
 			const deps_of = (entry, add_dynamic_css = false) =>
-				find_deps(client_manifest, posixify(path.relative(root, entry)), add_dynamic_css, root);
+				find_deps(
+					vite_client_manifest,
+					posixify(path.relative(root, entry)),
+					add_dynamic_css,
+					root
+				);
 
 			if (svelte_config.kit.output.bundleStrategy === 'split') {
 				const start = deps_of(`${runtime_directory}/client/entry.js`);
@@ -1490,7 +1472,7 @@ function kit({ svelte_config }) {
 							const entry = `${kit.outDir}/generated/client-optimized/nodes/${i}.js`;
 							const deps = deps_of(entry, true);
 							const file = resolve_symlinks(
-								client_manifest,
+								vite_client_manifest,
 								`${kit.outDir}/generated/client-optimized/nodes/${i}.js`,
 								root
 							).chunk.file;
@@ -1565,7 +1547,7 @@ function kit({ svelte_config }) {
 				kit,
 				manifest_data,
 				server_manifest,
-				client_manifest,
+				vite_client_manifest,
 				assets_path,
 				client_chunks,
 				svelte_config.kit.output,
@@ -1600,19 +1582,7 @@ function kit({ svelte_config }) {
 			);
 
 			if (service_worker_entry_file) {
-				// mirror client settings that we can't set in the environment config earlier
-				builder.environments.serviceWorker.config.define =
-					builder.environments.client.config.define;
-				builder.environments.serviceWorker.config.resolve.alias = [
-					...get_config_aliases(kit, vite_config.root)
-				];
-				builder.environments.serviceWorker.config.experimental.renderBuiltUrl = (filename) => {
-					return {
-						runtime: `new URL(${JSON.stringify(filename)}, location.href).pathname`
-					};
-				};
-
-				await builder.build(builder.environments.serviceWorker);
+				await build_service_worker(builder, config_aliases);
 			}
 
 			console.log(
@@ -1696,22 +1666,3 @@ function find_overridden_config(config, resolved_config, enforced_config, path,
 	}
 	return out;
 }
-
-/**
- * @param {import('types').ValidatedConfig} config
- */
-const create_service_worker_module = (config) => dedent`
-	if (typeof self === 'undefined' || self instanceof ServiceWorkerGlobalScope === false) {
-		throw new Error('This module can only be imported inside a service worker');
-	}
-
-	export const build = [];
-	export const files = [
-		${create_assets(config)
-			.filter((asset) => config.kit.serviceWorker.files(asset.file))
-			.map((asset) => `${s(`${config.kit.paths.base}/${asset.file}`)}`)
-			.join(',\n')}
-	];
-	export const prerendered = [];
-	export const version = ${s(config.kit.version.name)};
-`;
diff --git a/packages/kit/test/apps/options-2/.gitignore b/packages/kit/test/apps/options-2/.gitignore
new file mode 100644
index 000000000000..78a3ff3dcc6e
--- /dev/null
+++ b/packages/kit/test/apps/options-2/.gitignore
@@ -0,0 +1 @@
+test/temp-service-worker.js
\ No newline at end of file
diff --git a/packages/kit/test/apps/options-2/src/service-worker.js b/packages/kit/test/apps/options-2/src/service-worker.js
index 84bce78f173f..63eb293a5535 100644
--- a/packages/kit/test/apps/options-2/src/service-worker.js
+++ b/packages/kit/test/apps/options-2/src/service-worker.js
@@ -7,9 +7,6 @@
 import { base, build, version } from '$service-worker';
 import src from './image.jpg?url';
 
-// This gives `self` the correct types
-const self = /** @type {ServiceWorkerGlobalScope} */ (/** @type {unknown} */ (globalThis.self));
-
 //@ts-ignore
 self.base = base;
 //@ts-ignore
@@ -20,10 +17,12 @@ self.image_src = src;
 const name = `cache-${version}`;
 
 self.addEventListener('install', (event) => {
+	// @ts-expect-error
 	event.waitUntil(caches.open(name).then((cache) => cache.addAll(build)));
 });
 
 self.addEventListener('activate', (event) => {
+	// @ts-expect-error
 	event.waitUntil(
 		caches.keys().then(async (keys) => {
 			for (const key of keys) {
@@ -34,6 +33,7 @@ self.addEventListener('activate', (event) => {
 });
 
 self.addEventListener('fetch', (event) => {
+	// @ts-expect-error
 	const { request } = event;
 
 	if (request.method !== 'GET' || request.headers.has('range')) return;
diff --git a/packages/kit/test/apps/options-2/test/test.js b/packages/kit/test/apps/options-2/test/test.js
index c89dd18f4adf..61cd794290ba 100644
--- a/packages/kit/test/apps/options-2/test/test.js
+++ b/packages/kit/test/apps/options-2/test/test.js
@@ -1,4 +1,6 @@
 import process from 'node:process';
+import fs from 'node:fs';
+import path from 'node:path';
 import { expect } from '@playwright/test';
 import { test } from '../../../utils.js';
 
@@ -126,24 +128,36 @@ test.describe('Service worker', () => {
 		const response = await request.get('/basepath/service-worker.js');
 		const content = await response.text();
 
-		const fn = new Function('self', 'location', content);
-
-		const self = {
-			addEventListener: () => {},
-			base: null,
-			build: null
-		};
-
 		const pathname = '/basepath/service-worker.js';
 
-		fn(self, {
-			href: baseURL + pathname,
-			pathname
-		});
-
-		expect(self.base).toBe('/basepath');
-		expect(self.build?.[0]).toMatch(/\/basepath\/_app\/immutable\/bundle\.[\w-]+\.js/);
-		expect(self.image_src).toMatch(/\/basepath\/_app\/immutable\/assets\/image\.[\w-]+\.jpg/);
+		const temp = path.join(import.meta.dirname, 'temp-service-worker.js');
+		fs.writeFileSync(
+			temp,
+			`
+const location = {
+	href: ${JSON.stringify(baseURL + pathname)},
+	pathname: ${JSON.stringify(pathname)}
+};
+
+export const self = {
+	addEventListener: () => {},
+	base: null,
+	build: null
+};
+
+${content}
+`
+		);
+
+		const service_worker = await import(temp);
+
+		expect(service_worker.self.base).toBe('/basepath');
+		expect(service_worker.self.build?.[0]).toMatch(
+			/\/basepath\/_app\/immutable\/bundle\.[\w-]+\.js/
+		);
+		expect(service_worker.self.image_src).toMatch(
+			/\/basepath\/_app\/immutable\/assets\/image\.[\w-]+\.jpg/
+		);
 	});
 
 	test('does not register /basepath/service-worker.js', async ({ page }) => {