Implementing Differential Loading in an Angular Application

Differential loading, also known as selective loading, is a technique to load only the necessary modules or components of an Angular application based on the target environment (e.g., browser vs. server). This significantly improves initial load times and Time to Interactive (TTI), especially for server-side rendering (SSR) scenarios. This challenge asks you to implement differential loading for a simple Angular application to demonstrate the concept.

Problem Description

You are tasked with creating an Angular application that utilizes differential loading to optimize the initial bundle size for browser and server environments. The application will have a core module and an optional feature module (FeatureModule) containing a component (FeatureComponent) that displays a simple message.

What needs to be achieved:

1. Create a core Angular application with a basic component (AppComponent) that displays a welcome message.
2. Create a separate FeatureModule with a FeatureComponent that displays a specific message.
3. Configure Angular to only include FeatureModule in the browser build. The server build should not include FeatureModule.
4. Ensure that the FeatureComponent is accessible in the browser build after the initial load (e.g., through a button click or route).

Key Requirements:

• Use Angular's build configuration to achieve differential loading. Avoid manual code modifications to conditionally load modules at runtime.
• The server build should be smaller than the browser build.
• The application should function correctly in both browser and server environments.
• The FeatureComponent should be available in the browser build after the initial load.

Expected Behavior:

• Server Build: The server build should only contain the core application logic. The FeatureModule and FeatureComponent should be absent. The application should still function correctly, displaying the welcome message from AppComponent.
• Browser Build: The browser build should include both the core application and the FeatureModule. The application should initially display the welcome message from AppComponent. A mechanism (e.g., a button) should be present to trigger the display of the FeatureComponent's message.

Edge Cases to Consider:

• Ensure that the server-side rendering (SSR) process doesn't attempt to load the FeatureModule, preventing errors.
• Verify that the browser build correctly loads and renders the FeatureComponent after the initial load.
• Consider the impact of lazy loading routes within the FeatureModule on the differential loading strategy.

Examples

Example 1:

Input:  Angular CLI build for server (ng build --configuration=production)
Output: A smaller bundle containing only the core application. No FeatureModule is present.
Explanation: The server build configuration excludes the FeatureModule, resulting in a smaller initial payload.

Example 2:

Input: Angular CLI build for browser (ng build --configuration=production)
Output: A larger bundle containing both the core application and the FeatureModule.
Explanation: The browser build configuration includes the FeatureModule, providing access to its components.

Example 3: (Complex Scenario - Button Click)

Input: Browser build, initial load displays AppComponent's message. User clicks a "Show Feature" button.
Output: The FeatureComponent's message is displayed on the page.
Explanation: The browser build includes the FeatureModule, allowing it to be dynamically rendered after the initial load.

Constraints

• The application must be built using Angular CLI.
• The FeatureModule should be a separate module, not part of the core application.
• The solution should be relatively simple and easy to understand, focusing on the core concept of differential loading.
• The application should be deployable and runnable without significant modifications.
• The difference in bundle size between the server and browser builds should be noticeable (at least a 10% reduction in the server build).

Notes

• Angular's build configuration (angular.json) is the primary tool for achieving differential loading. Pay close attention to the configurations section and how it affects module inclusion.
• Consider using the buildTransferState feature if you are implementing SSR. This allows you to transfer data from the server to the client, which can be useful for lazy-loaded modules.
• Focus on configuring the build process correctly rather than writing complex runtime logic to conditionally load modules. The goal is to let Angular handle the differential loading during the build phase.
• Start with a basic Angular project and incrementally add the FeatureModule to understand the impact of the build configuration.