fix: service worker base path in dev mode (#12577)

Fixes #12039

.changeset/nice-geese-serve.md

@@ -0,0 +1,5 @@
+---
+'@sveltejs/kit': patch
+---
+
+fix: service worker base path in dev mode

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

@@ -462,7 +462,7 @@ export async function dev(vite, vite_config, svelte_config) {
 						res.writeHead(200, {
 							'content-type': 'application/javascript'
 						});
-						res.end(`import '${to_fs(resolved)}';`);
+						res.end(`import '${svelte_config.kit.paths.base}${to_fs(resolved)}';`);
 					} else {
 						res.writeHead(404);
 						res.end('not found');

packages/kit/test/apps/options-2/test/test.js

@@ -1,4 +1,6 @@
+import path from 'node:path';
 import process from 'node:process';
+import { fileURLToPath } from 'node:url';
 import { expect } from '@playwright/test';
 import { test } from '../../../utils.js';
 
@@ -73,7 +75,18 @@ test.describe('trailing slash', () => {
 });
 
 test.describe('Service worker', () => {
-	if (process.env.DEV) return;
+	if (process.env.DEV) {
+		test('import proxy /basepath/service-worker.js', async ({ request }) => {
+			const __dirname = path.dirname(fileURLToPath(import.meta.url));
+			const response = await request.get('/basepath/service-worker.js');
+			const content = await response.text();
+			expect(content).toEqual(
+				`import '${path.join('/basepath', '/@fs', __dirname, '../src/service-worker.js')}';`
+			);
+		});
+
+		return;
+	}
 
 	test('build /basepath/service-worker.js', async ({ baseURL, request }) => {
 		const response = await request.get('/basepath/service-worker.js');