One of the key performance bottlenecks in large-scale web applications is the initial load time. As Angular applications grow in size, the amount of JavaScript required to load upfront can become overwhelming — leading to sluggish load speeds and poor user experience. Fortunately, Angular provides a powerful built-in feature to solve this: Lazy Loading.

Lazy loading is a technique that helps you load feature modules only when they are needed, rather than loading the entire application at once. In this blog, we’ll explore how lazy loading works in Angular, how it helps improve performance, and how to implement it correctly in real-world applications.

What is Lazy Loading?

Lazy loading is a design pattern where modules, components, or routes are loaded on demand, rather than during the initial app bootstrap. It improves performance by:

• Reducing the initial bundle size
• Decreasing load times
• Enhancing the user experience by loading only what is needed
• Saving bandwidth for users on slow or mobile networks

In Angular, lazy loading is typically applied to feature modules configured via the Angular Router.

How Angular Loads Modules

Angular supports two types of module loading:

Type: Eager Loading
Description: Loads all modules at app startup (default)
Type: Lazy Loading

Description: Loads modules asynchronously when needed

By default, all modules in AppModule are loaded eagerly. For larger applications, this can lead to massive JavaScript bundles. Lazy loading helps reduce this burden.

How Lazy Loading Works in Angular

Angular uses route-based lazy loading to dynamically import feature modules using the loadChildren property in the route configuration.

Here's what happens under the hood:

When the app loads, only AppModule is loaded.

When a user navigates to a lazy-loaded route, Angular uses loadChildren to fetch the feature module asynchronously.

The new module is bootstrapped, and its components are rendered.

Real-World Example of Lazy Loading

Imagine an Angular app with three main sections:

/dashboard

/admin

/profile

We want to load admin and profile modules only when the user visits those pages.

**Step 1: Create Feature Modules
**bash code

ng generate module admin --route admin --module app.module
ng generate module profile --route profile --module app.module
Angular CLI automatically configures the routes and sets up loadChildren in AppRoutingModule.

ts code:

const routes: Routes = [
  { path: 'admin', loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule) },
  { path: 'profile', loadChildren: () => import('./profile/profile.module').then(m => m.ProfileModule) }
];

Code Splitting with Angular CLI

Angular CLI uses Webpack under the hood. With lazy loading enabled, Webpack automatically creates separate JavaScript bundles (chunks) for each lazy-loaded module.

Example output:

text

main.js        → AppModule
admin-admin-module.js → AdminModule
profile-profile-module.js → ProfileModule

This means users will only download main.js at startup, and the other modules only when they’re needed — a huge performance boost!

Verifying Lazy Loading Works

You can inspect lazy-loaded chunks using:

Browser DevTools → Network tab (filter by .js and observe lazy-loaded chunks)

Angular CLI build output

Lighthouse audit, which reports large JS payloads or unused code

Benefits of Lazy Loading in Angular

Reduced Initial Load Time
Users get to the app faster, as only essential code loads at startup.

Improved Performance on Mobile
Smaller payloads mean faster performance on slow or limited networks.

Better User Experience
Users perceive the app as more responsive, especially when modules are preloaded intelligently.

Cleaner Architecture
Encourages modular design by logically separating features.

Scalability
As the app grows, lazy loading keeps load time stable and manageable.

Common Mistakes to Avoid

Including lazy modules in AppModule imports
This will defeat lazy loading and load them eagerly.

Using services that aren’t provided in lazy modules
Ensure that services meant for lazy modules use providedIn: 'root' or are registered in the respective module.

Not setting up router paths correctly
Incorrect loadChildren usage or import paths can break lazy loading.

Shared Modules Misuse
Avoid importing feature modules into SharedModule. Keep reusable components only.

Preloading Strategies

Lazy loading can be paired with preloading to improve perceived performance. Angular provides built-in preloading strategies:

Built-In:

• NoPreloading (default)
• PreloadAllModules

Example:

ts code

RouterModule.forRoot(routes, { preloadingStrategy: PreloadAllModules })

You can also create custom preloading strategies to preload modules based on user roles, network speed, or app behavior.

Lazy Loading in Real Projects

In one of our Angular-based e-commerce platforms, we implemented lazy loading for:

• Product catalog
• Admin dashboards
• Cart & checkout
• User profile and order history

By splitting the app into lazy modules:

• The initial load time reduced by 55%
• Mobile bounce rate dropped significantly
• User engagement improved as pages loaded quicker

This has become a standard practice in our Angular development services, especially for large enterprise apps or apps targeting low-bandwidth users.

Best Practices for Lazy Loading in Angular

Modularize your app early – Design feature modules with lazy loading in mind from the beginning.

Leverage route guards – Prevent unauthorized lazy-loaded routes with CanLoad or CanActivate.

Use preloading wisely – Preload only what matters (e.g., frequently visited modules).

Bundle analyzer tools – Use source-map-explorer or Webpack Bundle Analyzer to visualize bundle sizes.

Test lazy loading – Use unit tests to verify that modules are correctly isolated and loaded.

When Not to Use Lazy Loading

While lazy loading is powerful, it's not always necessary. You may skip it when:

• The app is very small
• All routes are required at startup
• You're building a desktop or internal tool where load time isn’t critical

Conclusion

Lazy loading in Angular is one of the most effective strategies to optimize performance, reduce load times, and improve the user experience in large applications. By leveraging Angular’s built-in routing and modular design, developers can implement lazy loading with minimal effort while reaping significant performance benefits.

Whether you're building a multi-feature enterprise application or a content-heavy dashboard, implementing lazy loading the right way will help you scale smoothly and load smartly.

If you're looking for expert assistance in building performant, scalable Angular apps, our Angular development services include architecture planning, modularization, and full CI/CD pipelines with performance tuning.