Angular Route-based Lazy Loading

Lazy loading is a design pattern that delays the loading of non-essentials resources (modules, components, etc.) until they are actually needed.

In Angular applications certain parts of your application only loads when a user navigates to specific routes.

This results in:

• Faster initial page load
• Reduced bundle size
• Better resource utilization
• Improved performance

Code Splitting

Code splitting is the technical process that enables lazy loading.

Angular’s CLI and webpack handle this by:

1. Breaking the application into multiple bundles
2. Loading these bundles on demand
3. Managing dependencies between bundles

Implementing Route-based Lazy Loading

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

const routes: Routes = [
  { path: '', redirectTo: 'home', pathMatch: 'full' },
  {
    path: 'home',
    loadChildren: () => import('./home/home.module')
      .then(m => m.HomeModule)
  },
  {
    path: 'products',
    loadChildren: () => import('./products/products.module')
      .then(m => m.ProductsModule)
  }
];

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

Feature Module Setup

// products/products.module.ts
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { ProductsRoutingModule } from './products-routing.module';
import { ProductListComponent } from './product-list/product-list.component';
import { ProductDetailComponent } from './product-detail/product-detail.component';

@NgModule({
  declarations: [
    ProductListComponent,
    ProductDetailComponent
  ],
  imports: [
    CommonModule,
    ProductsRoutingModule
  ]
})
export class ProductsModule { }

// products/products-routing.module.ts
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { ProductListComponent } from './product-list/product-list.component';
import { ProductDetailComponent } from './product-detail/product-detail.component';

const routes: Routes = [
  {
    path: '',
    component: ProductListComponent
  },
  {
    path: ':id',
    component: ProductDetailComponent
  }
];

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

Lazy Loading Entire Route Groups

You can lazy load groups of related routes together:

// app-routing.module.ts
const routes: Routes = [
  {
    path: 'admin',
    loadChildren: () => import('./admin/admin.module')
      .then(m => m.AdminModule),
    canActivate: [authGuard]
  }
];

// admin/admin.module.ts
const routes: Routes = [
  {
    path: '',
    component: AdminDashboardComponent,
    children: [
      {
        path: 'users',
        loadChildren: () => import('./users/users.module')
          .then(m => m.UsersModule)
      },
      {
        path: 'settings',
        loadChildren: () => import('./settings/settings.module')
          .then(m => m.SettingsModule)
      }
    ]
  }
];