feat(@angular/ssr): add isMainModule function

goldens/public-api/angular/ssr/node/index.api.md

@@ -46,6 +46,9 @@ export interface CommonEngineRenderOptions {
 // @public
 export function createWebRequestFromNodeRequest(nodeRequest: IncomingMessage): Request;
 
+// @public
+export function isMainModule(url: string): boolean;
+
 // @public
 export function writeResponseToNodeResponse(source: Response, destination: ServerResponse): Promise<void>;
 

packages/angular/ssr/node/public_api.ts

@@ -16,3 +16,4 @@ export { AngularNodeAppEngine } from './src/app-engine';
 
 export { writeResponseToNodeResponse } from './src/response';
 export { createWebRequestFromNodeRequest } from './src/request';
+export { isMainModule } from './src/module';

packages/angular/ssr/node/src/module.ts

@@ -0,0 +1,30 @@
+/**
+ * @license
+ * Copyright Google LLC All Rights Reserved.
+ *
+ * Use of this source code is governed by an MIT-style license that can be
+ * found in the LICENSE file at https://angular.dev/license
+ */
+
+import { argv } from 'node:process';
+import { fileURLToPath } from 'node:url';
+
+/**
+ * Determines whether the provided URL represents the main entry point module.
+ *
+ * This function checks if the provided URL corresponds to the main ESM module being executed directly.
+ * It's useful for conditionally executing code that should only run when a module is the entry point,
+ * such as starting a server or initializing an application.
+ *
+ * It performs two key checks:
+ * 1. Verifies if the URL starts with 'file:', ensuring it is a local file.
+ * 2. Compares the URL's resolved file path with the first command-line argument (`process.argv[1]`),
+ *    which points to the file being executed.
+ *
+ * @param url The URL of the module to check. This should typically be `import.meta.url`.
+ * @returns `true` if the provided URL represents the main entry point, otherwise `false`.
+ * @developerPreview
+ */
+export function isMainModule(url: string): boolean {
+  return url.startsWith('file:') && argv[1] === fileURLToPath(url);
+}