Angular Build Optimization Challenge: Lazy Loading and Feature Modules

Angular applications can grow large, leading to slow initial load times and a degraded user experience. This challenge focuses on implementing build optimization techniques, specifically lazy loading and feature modules, to improve the performance of an Angular application. You'll be tasked with refactoring an existing application to split it into feature modules and lazily load them, reducing the initial bundle size and improving startup time.

Problem Description

You are given a basic Angular application with several components and services representing a simple e-commerce site. The application currently has all components and modules loaded eagerly during the initial build. Your task is to refactor this application by:

1. Identifying Feature Modules: Divide the application into logical feature modules (e.g., Products, Cart, Checkout, User).
2. Creating Feature Modules: Create separate Angular modules for each identified feature. Each module should contain its own components, services, and routing.
3. Implementing Lazy Loading: Configure the root module's routing to lazily load the feature modules. This means the feature modules will only be loaded when the user navigates to a route within that module.
4. Updating Routing: Adjust the root app-routing.module.ts to reflect the new lazy-loaded routes.
5. Maintaining Functionality: Ensure that the application's core functionality remains intact after the refactoring. All existing routes and features should still work as expected.

Expected Behavior:

• The initial bundle size should be significantly smaller after implementing lazy loading.
• Navigation to routes within a lazily loaded feature module should trigger the loading of that module's code.
• The application should function identically to its original state, with all features accessible.
• The application should load only the necessary modules for the initial view, improving startup time.

Edge Cases to Consider:

• Shared services or components that are used by multiple feature modules. Consider how to share these efficiently without increasing the initial bundle size. (Using a shared module is a good approach).
• Routes that require data to be loaded before rendering. Ensure that lazy-loaded modules handle data loading correctly.
• The impact of lazy loading on Angular's change detection.

Examples

Example 1:

Input: A basic Angular application with all components and modules loaded eagerly.  Assume a route `/products` exists and displays a list of products.

Output: The `/products` route is now part of a `ProductsModule` that is lazily loaded. When the user navigates to `/products`, the `ProductsModule` is downloaded and executed.

Explanation: The `app-routing.module.ts` now contains a route for `/products` that points to the `ProductsModule`.  The `ProductsModule` contains the component responsible for displaying the product list.

Example 2:

Input: An Angular application with a `CartModule` and a `CheckoutModule`.

Output: The `CartModule` and `CheckoutModule` are lazily loaded.  Navigation to `/cart` loads the `CartModule`, and navigation to `/checkout` loads the `CheckoutModule`.

Explanation: The `app-routing.module.ts` defines routes for `/cart` and `/checkout` that load the respective modules.

Constraints

• Angular Version: Assume Angular 16 or later.
• Bundle Size Reduction: Aim for a minimum 20% reduction in the initial bundle size. (This can be verified using Angular CLI's build stats).
• Code Quality: Maintain clean, readable, and well-documented code.
• Performance: Lazy loading should not introduce noticeable delays in route navigation.
• Input Application: You will be provided with a starter Angular application (see "Starter Application" below).

Notes

• Consider using Angular's RouterModule.forChild() method within your feature modules to define their routes.
• Think about how to structure your feature modules to promote reusability and maintainability.
• Use the Angular CLI to generate modules and routes.
• Utilize Angular's build stats to measure the impact of your optimizations. Run ng build --stats-json and analyze the generated stats.json file.
• A shared module can be used to hold services and components that are used by multiple feature modules.

Starter Application:

A simplified starter application will be provided separately. It contains a basic layout with a few components (e.g., AppComponent, HomeComponent, ProductListComponent) and a single AppRoutingModule. The goal is to refactor this application to incorporate lazy loading and feature modules as described above. The starter application will include a products.service.ts that fetches product data.