dev time service workers - closes #5479

.changeset/kind-dragons-poke.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+Run service worker during development

documentation/docs/30-advanced/40-service-workers.md

@@ -10,4 +10,12 @@ In SvelteKit, if you have a `src/service-worker.js` file (or `src/service-worker
 
 Inside the service worker you have access to the [`$service-worker` module](/docs/modules#$service-worker). If your Vite config specifies `define`, this will be applied to service workers as well as your server/client builds.
 
-Because it needs to be bundled (since browsers don't yet support `import` in this context), and depends on the client-side app's build manifest, **service workers only work in the production build, not in development**. To test it locally, use `vite preview`.
+The service worker is bundled for production, but not during development. For that reason, only browsers that support [modules in service workers](https://web.dev/es-modules-in-sw) will be able to use them at dev time. If you are manually registering your service worker, you will need to pass the `{ type: 'module' }` option in development:
+
+```js
+import { dev } from '$app/environment';
+
+navigator.serviceWorker.register('/service-worker.js', {
+	type: dev ? 'module' : 'classic'
+});
+```

packages/kit/src/core/sync/create_manifest_data/index.js

@@ -35,7 +35,7 @@ export default function create_manifest_data({
 /**
  * @param {import('types').ValidatedConfig} config
  */
-function create_assets(config) {
+export function create_assets(config) {
 	return list_files(config.kit.files.assets).map((file) => ({
 		file,
 		size: fs.statSync(path.resolve(config.kit.files.assets, file)).size,

packages/kit/src/exports/vite/dev/index.js

@@ -302,6 +302,22 @@ export async function dev(vite, vite_config, svelte_config) {
 					);
 				}
 
+				if (decoded === '/service-worker.js') {
+					const resolved = resolve_entry(svelte_config.kit.files.serviceWorker);
+
+					if (resolved) {
+						res.writeHead(200, {
+							'content-type': 'application/javascript'
+						});
+						res.end(`import '${resolved}';`);
+					} else {
+						res.writeHead(404);
+						res.end('not found');
+					}
+
+					return;
+				}
+
 				const hooks_file = svelte_config.kit.files.hooks.server;
 				/** @type {Partial<import('types').ServerHooks>} */
 				const user_hooks = resolve_entry(hooks_file)
@@ -451,7 +467,9 @@ export async function dev(vite, vite_config, svelte_config) {
 								.replace(/%sveltekit\.status%/g, String(status))
 								.replace(/%sveltekit\.error\.message%/g, message);
 						},
-						service_worker: false,
+						service_worker:
+							svelte_config.kit.serviceWorker.register &&
+							!!resolve_entry(svelte_config.kit.files.serviceWorker),
 						trailing_slash: svelte_config.kit.trailingSlash
 					},
 					{

packages/kit/src/exports/vite/index.js

@@ -18,6 +18,7 @@ import { get_config_aliases, get_app_aliases, get_env } from './utils.js';
 import { fileURLToPath } from 'node:url';
 import { create_static_module, create_dynamic_module } from '../../core/env.js';
 import { is_illegal, module_guard, normalize_id } from './graph_analysis/index.js';
+import { create_assets } from '../../core/sync/create_manifest_data/index.js';
 
 const cwd = process.cwd();
 
@@ -289,7 +290,7 @@ function kit() {
 
 		async resolveId(id) {
 			// treat $env/static/[public|private] as virtual
-			if (id.startsWith('$env/')) return `\0${id}`;
+			if (id.startsWith('$env/') || id === '$service-worker') return `\0${id}`;
 		},
 
 		async load(id, options) {
@@ -323,6 +324,8 @@ function kit() {
 						'public',
 						vite_config_env.command === 'serve' ? env.public : undefined
 					);
+				case '\0$service-worker':
+					return create_service_worker_module(svelte_config);
 			}
 		},
 
@@ -627,3 +630,22 @@ function find_overridden_config(config, resolved_config, enforced_config, path,
 
 	return out;
 }
+
+/**
+ * @param {import('types').ValidatedConfig} config
+ */
+const create_service_worker_module = (config) => `
+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 = [
+	${create_assets(config)
+		.filter((asset) => config.kit.serviceWorker.files(asset.file))
+		.map((asset) => `${JSON.stringify(`${config.kit.paths.base}/${asset.file}`)}`)
+		.join(',\n\t\t\t\t')}
+];
+export const prerendered = [];
+export const version = ${JSON.stringify(config.kit.version.name)};
+`;

packages/kit/src/runtime/server/page/render.js

@@ -288,12 +288,14 @@ export async function render_response({
 	}
 
 	if (options.service_worker) {
+		const opts = options.dev ? `, { type: 'module' }` : '';
+
 		// we use an anonymous function instead of an arrow function to support
 		// older browsers (https://github.com/sveltejs/kit/pull/5417)
 		const init_service_worker = `
 			if ('serviceWorker' in navigator) {
 				addEventListener('load', function () {
-					navigator.serviceWorker.register('${prefixed('service-worker.js')}');
+					navigator.serviceWorker.register('${prefixed('service-worker.js')}'${opts});
 				});
 			}
 		`;

packages/kit/types/ambient.d.ts

@@ -342,6 +342,7 @@ declare module '$app/stores' {
 declare module '$service-worker' {
 	/**
 	 * An array of URL strings representing the files generated by Vite, suitable for caching with `cache.addAll(build)`.
+	 * During development, this is be an empty array.
 	 */
 	export const build: string[];
 	/**
@@ -350,6 +351,7 @@ declare module '$service-worker' {
 	export const files: string[];
 	/**
 	 * An array of pathnames corresponding to prerendered pages and endpoints.
+	 * During development, this is be an empty array.
 	 */
 	export const prerendered: string[];
 	/**