Benefits of Lazy Loading in Angular Applications

Lazy loading is one of the most powerful optimization techniques available in Angular applications. It allows developers to load feature modules only when they are needed instead of loading the entire application bundle at once. This significantly improves performance, reduces initial loading time, and enhances the user experience — especially in large, enterprise-level applications.

This post explores the concept, advantages, and implementation of lazy loading in Angular in detail. We’ll also cover how it impacts performance, how to structure your application for modularity, and best practices for efficient usage.

1. Understanding Lazy Loading

In Angular, lazy loading refers to the practice of loading feature modules asynchronously when a user navigates to a specific route that requires them. Instead of downloading all code upfront (as in eager loading), Angular loads only the essential parts of the application initially.

When a user navigates to a lazy-loaded module, Angular fetches that module dynamically from the server.

This improves load performance and optimizes bandwidth usage, especially for applications with many features that are not required during the initial load.

2. How Lazy Loading Works

Angular uses the loadChildren property in the router configuration to enable lazy loading. Instead of directly importing the module, the module path is provided as a string, which Angular resolves when needed.

Example:

const routes: Routes = [
  {
path: 'dashboard',
loadChildren: () =&gt;
  import('./dashboard/dashboard.module').then(m =&gt; m.DashboardModule)  },
  {
path: 'settings',
loadChildren: () =&gt;
  import('./settings/settings.module').then(m =&gt; m.SettingsModule)  }
];

In this setup:

DashboardModule and SettingsModule are lazy-loaded.
They will only be loaded when the user navigates to /dashboard or /settings.

3. Eager Loading vs Lazy Loading

Eager Loading

Loads all feature modules at the start.
Increases initial load time.
Suitable for small applications or core modules used across the app.

Lazy Loading

Loads modules on demand.
Reduces initial bundle size.
Ideal for large, modular applications with multiple independent features.

Example comparison:

// Eager loading
import { DashboardModule } from './dashboard/dashboard.module';

@NgModule({
  imports: [BrowserModule, DashboardModule]
})
export class AppModule {}

// Lazy loading
const routes: Routes = [
  { path: 'dashboard', loadChildren: () => import('./dashboard/dashboard.module').then(m => m.DashboardModule) }
];

4. Why Use Lazy Loading?

Lazy loading provides several performance and structural benefits. Let’s look at the major ones in depth.

4.1 Faster Initial Load Time

By loading only the essential parts of your application at startup, Angular minimizes the size of the main bundle. This results in:

Faster loading of the homepage.
Quicker interaction readiness for users.
Lower Time to Interactive (TTI) metrics.

Users accessing your site for the first time won’t have to wait for unnecessary code to download.

4.2 Better Performance in Large Applications

For large-scale Angular applications with multiple modules (e.g., admin, user, settings, reports, etc.), loading everything at once can drastically slow down performance.

Lazy loading ensures that only the current route’s module is loaded, keeping memory usage and processing time optimized.

4.3 Separation of Features into Smaller Chunks

Lazy loading enforces modular architecture by splitting the application into smaller, self-contained modules. Each module:

Can be developed and tested independently.
Is responsible for a specific feature or functionality.
Is only loaded when required.

This structure leads to better code organization and maintainability.

4.4 Efficient Use of Bandwidth

Lazy loading ensures that users download only what they need. This is especially beneficial for:

Mobile users with limited data plans.
Users in regions with slow internet connections.

By reducing the total amount of downloaded data upfront, the application becomes more bandwidth-efficient.

4.5 Scalability

Lazy loading allows an app to scale easily. As new features are added, they can be encapsulated into new modules without impacting the main application bundle size.

Each feature can be independently lazy-loaded, ensuring consistent performance even as the application grows.

4.6 Improved User Experience

Users experience faster load times and smoother navigation. Since only necessary modules load per route, transitions feel more responsive, and UI rendering becomes faster.

5. Setting Up Lazy Loading Step-by-Step

Let’s go through how to configure lazy loading in an Angular project.

Step 1: Create a Feature Module

ng generate module dashboard --route dashboard --module app.module

This automatically creates a DashboardModule and configures lazy loading in the router.

Step 2: Add Routing in the Feature Module

Inside dashboard-routing.module.ts:

const routes: Routes = [
  { path: '', component: DashboardComponent }
];

@NgModule({
  imports: [RouterModule.forChild(routes)],
  exports: [RouterModule]
})
export class DashboardRoutingModule {}

Step 3: Declare Components in the Feature Module

Inside dashboard.module.ts:

@NgModule({
  declarations: [DashboardComponent],
  imports: [CommonModule, DashboardRoutingModule]
})
export class DashboardModule {}

Step 4: Configure Main Routing

In app-routing.module.ts:

const routes: Routes = [
  {
path: 'dashboard',
loadChildren: () =&gt;
  import('./dashboard/dashboard.module').then(m =&gt; m.DashboardModule)  },
  { path: '', redirectTo: 'dashboard', pathMatch: 'full' }
];

6. Preloading Strategy for Lazy Loading

While lazy loading improves performance, sometimes certain modules are frequently accessed (e.g., dashboard or profile). You can preload them in the background using Angular’s PreloadAllModules strategy.

import { RouterModule, PreloadAllModules } from '@angular/router';

@NgModule({
  imports: [
RouterModule.forRoot(routes, { preloadingStrategy: PreloadAllModules })  ],
  exports: [RouterModule]
})
export class AppRoutingModule {}

This approach preloads all lazy modules after the app is initially loaded, improving navigation speed for subsequent routes.

7. Route-Level Lazy Loading Example

You can lazy-load multiple modules independently:

const routes: Routes = [
  { path: 'users', loadChildren: () => import('./users/users.module').then(m => m.UsersModule) },
  { path: 'orders', loadChildren: () => import('./orders/orders.module').then(m => m.OrdersModule) },
  { path: 'reports', loadChildren: () => import('./reports/reports.module').then(m => m.ReportsModule) }
];

Each module will load separately when its corresponding route is visited.

8. Combining Lazy Loading with Guards

You can use route guards to restrict access to lazy-loaded modules.

{
  path: 'admin',
  loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule),
  canLoad: [AuthGuard]
}

Here, canLoad prevents the module from loading until the guard condition is met.

9. Lazy Loading and Shared Modules

When using shared components, pipes, or directives across multiple lazy-loaded modules, it’s best to create a SharedModule to avoid duplication.

@NgModule({
  declarations: [CustomPipe, SharedComponent],
  exports: [CustomPipe, SharedComponent],
  imports: [CommonModule]
})
export class SharedModule {}

Then import it in each feature module that needs those shared resources.

10. Performance Benefits of Lazy Loading

The impact of lazy loading is clearly measurable:

Reduced initial bundle size.
Faster first contentful paint (FCP).
Better time-to-interactive (TTI) metrics.
Improved Lighthouse performance scores.
Optimized Core Web Vitals.

Lazy loading ensures your Angular application scales well across devices and network conditions.

11. Code Splitting Behind the Scenes

Under the hood, Angular uses Webpack for module bundling. When you define lazy-loaded routes, Webpack automatically splits your application into multiple chunks.

Each chunk (bundle) is fetched dynamically when required, enabling efficient loading and caching.

12. Best Practices for Lazy Loading

Lazy-load all feature modules not required at app startup.
Keep shared modules lightweight to avoid large duplicated bundles.
Avoid circular dependencies between modules.
Use route guards with canLoad to control access.
Implement preloading strategies for frequently accessed modules.
Use custom preloading strategies to control what loads in the background.
Analyze bundle size using Angular CLI’s ng build --stats-json and visualization tools.

13. Example: Custom Preloading Strategy

You can define a custom preloading strategy to selectively preload specific modules.

@Injectable({ providedIn: 'root' })
export class CustomPreloadingStrategy implements PreloadingStrategy {
  preload(route: Route, load: () => Observable<any>): Observable<any> {
return route.data &amp;&amp; route.data&#91;'preload'] ? load() : of(null);  }
}

Usage:

const routes: Routes = [
  { path: 'dashboard', loadChildren: () => import('./dashboard/dashboard.module').then(m => m.DashboardModule), data: { preload: true } },
  { path: 'settings', loadChildren: () => import('./settings/settings.module').then(m => m.SettingsModule) }
];

14. Testing Lazy-Loaded Modules

You can verify lazy-loaded routes using Angular’s testing utilities:

it('should lazy load dashboard module', async () => {
  await router.navigate(['/dashboard']);
  expect(location.path()).toBe('/dashboard');
});

This ensures your lazy-loaded modules load correctly and perform as expected.