From 318c164d1f58b919545bca005df225bc8a55a58d Mon Sep 17 00:00:00 2001
From: Charles Lyding <19598772+clydin@users.noreply.github.com>
Date: Wed, 12 Mar 2025 15:21:36 -0400
Subject: [PATCH] refactor(@angular/build): define an internal ngHmrMode value

An `ngHmrMode` boolean value will now be defined within application bundles.
The value is based on the development server's `hmr` option with `true`
when HMR is enabled and `false` when disabled. For all application builds,
the value will be `false`. `ngHmrMode` is similar in behavior to `ngServeMode`
or `ngDevMode`. It will not be present in the output code unless referenced
and in those cases only the final boolean value will be present if not optimized
out of the final code.
The value is not considered part of the public API and may change in the future.
---
 .../tests/behavior/component-updates_spec.ts  | 34 +++++++++++++++++++
 .../tools/esbuild/application-code-bundle.ts  |  1 +
 2 files changed, 35 insertions(+)

diff --git a/packages/angular/build/src/builders/dev-server/tests/behavior/component-updates_spec.ts b/packages/angular/build/src/builders/dev-server/tests/behavior/component-updates_spec.ts
index d471d487c5..742e07ea3b 100644
--- a/packages/angular/build/src/builders/dev-server/tests/behavior/component-updates_spec.ts
+++ b/packages/angular/build/src/builders/dev-server/tests/behavior/component-updates_spec.ts
@@ -47,5 +47,39 @@ describeServeBuilder(executeDevServer, DEV_SERVER_BUILDER_INFO, (harness, setupT
       expect(response?.headers.get('Cache-Control')).toEqual('no-cache');
       expect(output).toBe('');
     });
+
+    it('sets ngHmrMode define to true when HMR is enabled', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+        hmr: true,
+      });
+
+      await harness.writeFile(
+        'src/main.ts',
+        'declare const ngHmrMode: boolean; console.log(`HMR=${ngHmrMode}`);',
+      );
+
+      const { result, content } = await executeOnceAndFetch(harness, 'main.js');
+
+      expect(result?.success).toBeTrue();
+      expect(content).toContain('HMR=${true}');
+    });
+
+    it('sets ngHmrMode define to false when HMR is disabled', async () => {
+      harness.useTarget('serve', {
+        ...BASE_OPTIONS,
+        hmr: false,
+      });
+
+      await harness.writeFile(
+        'src/main.ts',
+        'declare const ngHmrMode: boolean; console.log(`HMR=${ngHmrMode}`);',
+      );
+
+      const { result, content } = await executeOnceAndFetch(harness, 'main.js');
+
+      expect(result?.success).toBeTrue();
+      expect(content).toContain('HMR=${false}');
+    });
   });
 });
diff --git a/packages/angular/build/src/tools/esbuild/application-code-bundle.ts b/packages/angular/build/src/tools/esbuild/application-code-bundle.ts
index 58bdd78c2d..df7371e3a4 100644
--- a/packages/angular/build/src/tools/esbuild/application-code-bundle.ts
+++ b/packages/angular/build/src/tools/esbuild/application-code-bundle.ts
@@ -600,6 +600,7 @@ function getEsBuildCommonOptions(options: NormalizedApplicationBuildOptions): Bu
       ...(optimizationOptions.scripts ? { 'ngDevMode': 'false' } : undefined),
       'ngJitMode': jit ? 'true' : 'false',
       'ngServerMode': 'false',
+      'ngHmrMode': options.templateUpdates ? 'true' : 'false',
     },
     loader: loaderExtensions,
     footer,