Implement Lazy Loading for Angular Modules

This challenge focuses on implementing lazy loading for Angular modules, a crucial technique for improving application performance. By deferring the loading of certain parts of your application until they are actually needed, you can significantly reduce the initial bundle size and speed up the time to interactive for your users.

Problem Description

Your task is to refactor an existing Angular application to implement lazy loading for a specific feature module. The application currently loads all modules eagerly, leading to a larger initial download. You need to modify the routing configuration to load a designated "Product List" module only when the user navigates to its corresponding route.

Key Requirements:

• Identify a feature module (e.g., ProductModule) that can be lazily loaded.
• Update the main application's routing module (app-routing.module.ts) to configure a lazy-loaded route for this feature module.
• Ensure that when the user navigates to the lazy-loaded route, the module is loaded, and its associated component is rendered.
• When the user navigates away from the lazy-loaded route, the module should ideally be unloaded or its resources freed up (though explicit unloading is often handled by Angular's router and not always a direct implementation step unless specific lifecycle hooks are used for cleanup).
• The rest of the application's functionality should remain unaffected.

Expected Behavior:

1. When the application initially loads, only the core modules should be downloaded.
2. When the user clicks a link or navigates directly to the route associated with the ProductModule, the browser will download the JavaScript chunk for ProductModule.
3. Once downloaded, the ProductModule will be initialized, and its default component (e.g., ProductListComponent) will be displayed.
4. Navigating away from this route will not trigger the immediate reloading of the ProductModule until it's needed again.

Edge Cases:

• What happens if the lazy-loaded module fails to load? The application should gracefully handle this, perhaps by showing an error message.
• Ensure the path for the lazy-loaded module is correctly specified.

Examples

Let's assume a simplified Angular project structure:

src/
├── app/
│   ├── app-routing.module.ts
│   ├── app.component.html
│   ├── app.component.ts
│   ├── core/        // Core module (eagerly loaded)
│   │   ├── core.module.ts
│   │   └── ...
│   └── products/    // Feature module to be lazily loaded
│       ├── product-list/
│       │   ├── product-list.component.html
│       │   ├── product-list.component.ts
│       │   └── ...
│       ├── products.module.ts
│       └── products-routing.module.ts
└── ...

Example 1: Initial Load

• Input: User opens the application in their browser and lands on the default route.
• Output: The app.component and core.module are loaded. The JavaScript chunk for products.module.ts is not downloaded yet.
• Explanation: The application starts with its essential components and modules.

Example 2: Navigating to Lazy-Loaded Route

• Input: User clicks on a link in app.component.html that points to /products.
• Output:
  • The browser initiates a network request to download the products.module.js (or similar chunk name generated by the build process).
  • Once downloaded, the ProductsModule is initialized.
  • The ProductListComponent (defined in products-routing.module.ts for the /products route) is rendered within the router-outlet.
• Explanation: The router detects a route that requires a lazily loaded module, fetches it, and then renders the corresponding component.

Example 3: Navigating Away and Back

• Input:
  1. User navigates to /products. ProductsModule is loaded and ProductListComponent is displayed.
  2. User navigates to another route (e.g., /dashboard which is part of the core).
  3. User navigates back to /products.
• Output:
  • After step 2, the ProductsModule's JavaScript might be cached by the browser, or in some configurations, the router might manage its lifecycle.
  • In step 3, if the module is cached and the router is configured to reuse modules, the ProductListComponent is rendered quickly without a new download. If not cached, it will be downloaded again.
• Explanation: Demonstrates how Angular's router handles subsequent navigations to lazily loaded modules, leveraging browser caching or module management.

Constraints

• The Angular version used is Angular 12 or later.
• The solution must be implemented using TypeScript.
• The build process should generate separate JavaScript chunks for the lazily loaded module.
• The AppModule and its routing should be modified; however, the core functionality of other modules should remain intact.

Notes

• Lazy loading in Angular is primarily configured within the app-routing.module.ts file using the loadChildren property of Route objects.
• The loadChildren property typically points to the module path and the module class using a specific syntax (e.g., './products/products.module#ProductsModule' in older Angular versions, or using an import function in newer versions like () => import('./products/products.module').then(m => m.ProductsModule)). You should aim for the modern import function syntax.
• Consider how you will represent the "Products" feature. You'll likely need a ProductsModule, a ProductsRoutingModule, and a component within that module (e.g., ProductListComponent).
• Think about how the main application will link to this lazy-loaded feature. You'll need a navigation element (e.g., an <a> tag with routerLink) in your AppComponent's template.
• The build tool (Angular CLI) is responsible for creating the separate bundles for lazy-loaded modules. Your task is to configure the router correctly to trigger this behavior.
• For error handling during module loading, you can explore the paramsInheritanceStrategy, onSameUrlNavigation, and custom UrlMatcher configurations, though a basic implementation of loadChildren is the primary goal.