From 8e4bb0e4cd477f42519ebb0fcc9236fd4d90c270 Mon Sep 17 00:00:00 2001
From: Alan Agius <17563226+alan-agius4@users.noreply.github.com>
Date: Fri, 4 Sep 2026 07:19:55 +0000
Subject: [PATCH] fix(@angular/build): default preloadInitial to false when
 serviceWorker is enabled

When a service worker is enabled, application assets are prefetched and served from
Cache Storage. Emitting `<link rel="modulepreload">` hints for initial shared chunks
causes Chromium to discard them with a "cross-world service worker resource mismatch"
warning on repeat visits, as well as triggering redundant network fetches.

This change sets the default of `preloadInitial` to `false` when the `serviceWorker`
option is enabled, while still allowing developers to explicitly override it if desired.

Fixes #34022
---
 .../build/src/builders/application/options.ts |  9 +++--
 .../src/builders/application/schema.json      |  1 -
 .../tests/options/service-worker_spec.ts      | 36 +++++++++++++++++++
 3 files changed, 43 insertions(+), 3 deletions(-)

diff --git a/packages/angular/build/src/builders/application/options.ts b/packages/angular/build/src/builders/application/options.ts
index abe3298aa093..dc53d55b61f0 100644
--- a/packages/angular/build/src/builders/application/options.ts
+++ b/packages/angular/build/src/builders/application/options.ts
@@ -384,6 +384,8 @@ export async function normalizeOptions(
         ? INDEX_HTML_CSR
         : indexBaseName;
 
+    const preloadInitialDefault = !options.serviceWorker;
+
     indexHtmlOptions = {
       input: indexInput,
       output: indexOutput,
@@ -395,8 +397,11 @@ export async function normalizeOptions(
         // [name, esm]
       ] as [string, boolean][],
       transformer: extensions?.indexHtmlTransformer,
-      // Preload initial defaults to true
-      preloadInitial: typeof options.index !== 'object' || (options.index.preloadInitial ?? true),
+      // Preload initial defaults to false when using a service worker, true otherwise
+      preloadInitial:
+        typeof options.index === 'object'
+          ? (options.index?.preloadInitial ?? preloadInitialDefault)
+          : preloadInitialDefault,
     };
   }
 
diff --git a/packages/angular/build/src/builders/application/schema.json b/packages/angular/build/src/builders/application/schema.json
index 8bf30aec8298..4e20cdd0da07 100644
--- a/packages/angular/build/src/builders/application/schema.json
+++ b/packages/angular/build/src/builders/application/schema.json
@@ -520,7 +520,6 @@
             },
             "preloadInitial": {
               "type": "boolean",
-              "default": true,
               "description": "Generates 'preload', 'modulepreload', and 'preconnect' link elements for initial application files and resources."
             }
           },
diff --git a/packages/angular/build/src/builders/application/tests/options/service-worker_spec.ts b/packages/angular/build/src/builders/application/tests/options/service-worker_spec.ts
index 444babc37a02..8711f36211ba 100644
--- a/packages/angular/build/src/builders/application/tests/options/service-worker_spec.ts
+++ b/packages/angular/build/src/builders/application/tests/options/service-worker_spec.ts
@@ -89,6 +89,42 @@ describeBuilder(buildApplication, APPLICATION_BUILDER_INFO, (harness) => {
       expect(JSON.parse(config)).toEqual(jasmine.objectContaining({ index: '/index.csr.html' }));
     });
 
+    it('should not generate initial modulepreload hints by default when service worker is enabled', async () => {
+      // Setup an initial chunk usage for JS
+      await harness.writeFile('src/a.ts', 'console.log("TEST");');
+      await harness.writeFile('src/b.ts', 'import "./a";');
+      await harness.writeFile('src/main.ts', 'import "./a";\n(() => import("./b"))();');
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+        serviceWorker: true,
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+      harness.expectFile('dist/browser/index.html').content.not.toContain('modulepreload');
+    });
+
+    it('should generate initial modulepreload hints when preloadInitial is explicitly true and service worker is enabled', async () => {
+      // Setup an initial chunk usage for JS
+      await harness.writeFile('src/a.ts', 'console.log("TEST");');
+      await harness.writeFile('src/b.ts', 'import "./a";');
+      await harness.writeFile('src/main.ts', 'import "./a";\n(() => import("./b"))();');
+
+      harness.useTarget('build', {
+        ...BASE_OPTIONS,
+        serviceWorker: true,
+        index: {
+          input: 'src/index.html',
+          preloadInitial: true,
+        },
+      });
+
+      const { result } = await harness.executeOnce();
+      expect(result?.success).toBeTrue();
+      harness.expectFile('dist/browser/index.html').content.toContain('modulepreload');
+    });
+
     it('should write JS-imported CSS chunk to browser dist when SSR is enabled', async () => {
       await harness.modifyFile('src/tsconfig.app.json', (content) => {
         const tsConfig = JSON.parse(content);