Applying Lazy Loading for Angular Modules

Explain and illustrate how to implement lazy loading for Angular modules to improve app loading times.

// app-routing.module.ts
import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';

// Define routes
const routes: Routes = [
  {
    path: 'feature',
    loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule)
  }
];

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

This code sets up lazy loading for a feature module within an Angular application. It defines a route configuration that uses the `loadChildren` syntax to dynamically import the `FeatureModule` when the 'feature' path is accessed for the first time. This delays the loading of the module until it is actually required.

// feature.module.ts
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { FeatureRoutingModule } from './feature-routing.module';

@NgModule({
  declarations: [
    // Your components here
  ],
  imports: [
    CommonModule,
    FeatureRoutingModule
  ]
})
export class FeatureModule {}

This is the code for a typical module in Angular which could be lazily loaded. The `FeatureModule` includes its own routing module `FeatureRoutingModule`, which would define child routes for this module. By separating the module like this and only referring to it in the `AppRoutingModule` via `loadChildren`, the `FeatureModule` will be loaded lazily.

// feature-routing.module.ts
import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { FeatureComponent } from './feature.component';

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

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

This is the routing module for the feature module (`FeatureModule`) which will be loaded lazily. It defines `FeatureComponent` as the default component for this module. The `RouterModule.forChild` method is used to declare child routes, which nest under the parent route as defined in the application's main routing module.