Understanding Eager Loading vs Lazy Loading in Angular

In Angular development, the strategy you choose for module loading—whether eager loading or lazy loading—can significantly impact both the performance and user experience of your application. This article explores the benefits of both approaches using practical examples from Angular's routing configuration.

Eager Loading in Angular

Eager loading involves loading all necessary modules and components at application startup, regardless of whether they are immediately needed or not. This approach ensures that all resources are available upfront, simplifying navigation but potentially increasing initial load times. Let's examine the benefits and implementation of eager loading:

Benefits of Eager Loading

1. Immediate Availability: All modules and components are loaded upfront, ensuring that they are available immediately when navigating to their respective routes. This can provide a seamless user experience without delay.
2. Simplified Routing Setup: Eager loading simplifies the routing configuration by loading all modules at application startup. This approach is straightforward and ensures that all dependencies are available from the beginning.

Implementation of Eager Loading

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { HomeComponent } from './home/home.component';
import { CustomersModule } from './customers/customers.module';
import { OrdersModule } from './orders/orders.module';
const routes: Routes = [
  {
    path: 'customers',
    loadChildren: () => CustomersModule,
  },
  {
    path: 'orders',
    loadChildren: () => OrdersModule,
  },
  {
    path: '',
    component: HomeComponent,
  },
];
@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule],
})
export class AppRoutingModule {}

Lazy Loading in Angular

Lazy loading is a technique where modules are loaded asynchronously only when the user navigates to their respective routes. This approach helps in reducing the initial bundle size of the application by loading only the necessary modules when they are required. Let's explore the benefits and implementation of lazy loading:

Benefits of Lazy Loading

1. Optimized Initial Load Time: Lazy loading improves application startup performance by loading modules on-demand as users navigate through the application. This reduces the initial load time and enhances the overall responsiveness of the application.
2. Efficient Resource Management: By loading modules dynamically, lazy loading optimizes resource usage and memory footprint. It ensures that only the required modules and components are loaded, which is beneficial for larger applications with complex routing and extensive feature modules.

Implementation of Lazy Loading

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { HomeComponent } from './home/home.component';
const routes: Routes = [
  {
    path: 'customers',
    loadChildren: () =>
      import('./customers/customers.module').then((m) => m.CustomersModule),
  },
  {
    path: 'orders',
    loadChildren: () =>
      import('./orders/orders.module').then((m) => m.OrdersModule),
  },
  {
    path: '',
    component: HomeComponent,
  },
];
@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule],
})
export class AppRoutingModule {}

Comparing Eager Loading vs Lazy Loading
 

Performance Impact

• Eager Loading: Increases initial load time due to loading all modules upfront. Provides immediate availability but may result in longer startup times.
• Lazy Loading: Optimizes initial load time by loading modules only when required. Enhances performance and resource management, especially in larger applications.

Implementation Considerations

• Eager Loading: Suitable for smaller applications or scenarios where immediate availability of modules is preferred. Simplifies routing setup and ensures predictable behavior.
• Lazy Loading: Recommended for large-scale applications with complex routing and extensive feature modules. Provides granular control over module loading and optimizes initial load times.

Conclusion

Understanding the benefits and implementation of eager loading and lazy loading in Angular is essential for designing scalable, performant applications. By leveraging eager loading, you ensure immediate availability of modules and simplify initial setup. On the other hand, lazy loading optimizes performance by loading modules on-demand, enhancing resource management and responsiveness. Choose the loading strategy based on your application's size, complexity, and performance requirements to achieve an optimal balance between functionality and user experience.