Angular Interview Questions

Lazy loading in Angular is a design pattern that loads feature modules on demand, rather than at the start of the application. This can significantly improve the application's performance by reducing the initial load time. Lazy loading is typically implemented using Angular's Router and the loadChildren property.

Steps to Lazy Load a Module in Angular:

1. Create a Feature Module:

   • First, create a feature module that you want to lazy load.
   • Example:

     ng generate module feature --route feature --module app.module

   • This command generates a module and configures lazy loading for it automatically.

2. Configure Routes for Lazy Loading:

   • Define a route in the AppRoutingModule that uses the loadChildren property to specify the module to load.
   • Example:

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

3. Update the Feature Module:

   • Ensure the feature module has its own routing module to handle the routes specific to that module.
   • Example:

     import { NgModule } from '@angular/core';
     import { CommonModule } from '@angular/common';
     import { RouterModule, Routes } from '@angular/router';
     import { FeatureComponent } from './feature/feature.component';
     
     const routes: Routes = [
       { path: '', component: FeatureComponent }
     ];
     
     @NgModule({
       declarations: [FeatureComponent],
       imports: [
         CommonModule,
         RouterModule.forChild(routes)
       ]
     })
     export class FeatureModule { }

4. Verify and Test:

   • Navigate to the lazy-loaded route (/feature in this case) to verify that the module is loaded on demand.

Example Walkthrough:

1. Generating a Feature Module:

   • Use Angular CLI to generate a feature module and a component.

     ng generate module admin --route admin --module app.module

   • This command creates AdminModule and configures it for lazy loading with a default route.

2. Setting Up Routing in AppRoutingModule:

   • Update the AppRoutingModule to lazy load the AdminModule.

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

3. Configuring AdminModule:

   • Ensure AdminModule has its own routing setup.

     import { NgModule } from '@angular/core';
     import { CommonModule } from '@angular/common';
     import { RouterModule, Routes } from '@angular/router';
     import { AdminComponent } from './admin/admin.component';
     
     const routes: Routes = [
       { path: '', component: AdminComponent }
     ];
     
     @NgModule({
       declarations: [AdminComponent],
       imports: [
         CommonModule,
         RouterModule.forChild(routes)
       ]
     })
     export class AdminModule { }

4. Lazy Load Verification:

   • Serve the application using ng serve.
   • Navigate to http://localhost:4200/admin.
   • The AdminModule and its components should load only when this route is accessed.

Benefits of Lazy Loading:

1. Improved Performance:

   • Reduces the initial load time by loading only the necessary modules and components initially.
   • Additional modules are loaded on demand, which can improve perceived performance.

2. Optimized Resource Usage:

   • Loads code only when needed, which can save bandwidth and reduce the amount of memory used by the application.

3. Scalability:

   • Makes it easier to manage large applications by breaking them into smaller, more manageable modules.

In Summary:

Lazy loading in Angular is achieved by configuring routes with the loadChildren property, which defers the loading of feature modules until they are needed. This approach enhances application performance and resource efficiency by loading code on demand. The process involves creating a feature module, setting up routing for lazy loading, and ensuring the feature module has its own routing configuration. By implementing lazy loading, Angular applications become more scalable and responsive, providing a better user experience.