Preloading strategies in Angular - Interactive Code Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to enable preloading of all lazy-loaded modules in Angular.

Angular

RouterModule.forRoot(routes, { preloadingStrategy: [1] })

Drag options to blanks, or click blank then click option'

AEagerLoading

BNoPreloading

CLazyLoadModules

DPreloadAllModules

Attempts:

3 left

💡 Hint

Common Mistakes

Using NoPreloading disables preloading.

LazyLoadModules is not a valid Angular preloading strategy.

The PreloadAllModules strategy tells Angular to preload all lazy-loaded modules after the app loads.

2fill in blank

medium

Complete the code to import the Angular preloading strategies module.

Angular

import { [1] } from '@angular/router';

Drag options to blanks, or click blank then click option'

APreloadAllModules

BNoPreloading

CRouterModule

DPreloadingStrategy

Attempts:

3 left

💡 Hint

Common Mistakes

Importing RouterModule instead of PreloadAllModules.

Using NoPreloading when you want to preload.

You import PreloadAllModules from @angular/router to use it as a preloading strategy.

3fill in blank

hard

Fix the error in the code to correctly set the preloading strategy to no preloading.

Angular

RouterModule.forRoot(routes, { preloadingStrategy: [1] })

Drag options to blanks, or click blank then click option'

APreloadAllModules

BNoPreloading

CLazyLoadStrategy

DEagerLoad

Attempts:

3 left

💡 Hint

Common Mistakes

Using PreloadAllModules when you want no preloading.

Using invalid strategy names.

NoPreloading disables preloading of lazy-loaded modules.

4fill in blank

hard

Fill both blanks to create a custom preloading strategy class that implements Angular's PreloadingStrategy interface.

Angular

export class CustomPreloadingStrategy implements [1] {
  preload(route: Route, load: () => Observable<any>): Observable<any> {
    if (route.data && route.data.[2]) {
      return load();
    } else {
      return of(null);
    }
  }
}

Drag options to blanks, or click blank then click option'

APreloadingStrategy

BRouterModule

Cpreload

DpreloadRoute

Attempts:

3 left

💡 Hint

Common Mistakes

Using RouterModule instead of PreloadingStrategy.

Using wrong method names like preloadRoute.

The class must implement PreloadingStrategy and define the preload method.

5fill in blank

hard

Fill all three blanks to configure the router with a custom preloading strategy and enable preloading for routes with data property 'preload: true'.

Angular

RouterModule.forRoot(routes, { preloadingStrategy: [1] })

const routes: Routes = [
  {
    path: 'feature',
    loadChildren: () => import('./feature/feature.module').then(m => m.FeatureModule),
    data: { [2]: true }
  },
  {
    path: 'other',
    loadChildren: () => import('./other/other.module').then(m => m.OtherModule),
    data: { [3]: false }
  }
];

Drag options to blanks, or click blank then click option'

ACustomPreloadingStrategy

Bpreload

DNoPreloading

Attempts:

3 left

💡 Hint

Common Mistakes

Using NoPreloading disables all preloading.

Using different data property names than 'preload'.

Use CustomPreloadingStrategy as the preloading strategy. The routes use the preload data property to control preloading.

Practice

1. What is the main purpose of preloading strategies in Angular?

easy

A. To load lazy modules in the background to improve navigation speed

B. To prevent any modules from loading until explicitly requested

C. To compile all modules at build time for faster startup

D. To automatically update Angular to the latest version

Solution

1. Step 1: Understand lazy loading in Angular

   Lazy loading delays loading modules until needed, which can slow navigation initially.

2. Step 2: Role of preloading strategies

   Preloading strategies load lazy modules in the background after app startup to speed up future navigation.

3. Final Answer:

   To load lazy modules in the background to improve navigation speed -> Option A

4. Quick Check:

   Preloading = background loading for faster navigation [OK]

Hint: Preloading means loading modules quietly before needed [OK]

Common Mistakes:

• Confusing preloading with eager loading
• Thinking preloading disables lazy loading
• Assuming preloading updates Angular versions

2. Which of the following is the correct way to enable preloading of all lazy modules in Angular routing?

easy

A. RouterModule.forRoot(routes, { preloadingStrategy: PreloadAllModules })

B. RouterModule.forRoot(routes, { preload: true })

C. RouterModule.forRoot(routes, { lazyLoad: true })

D. RouterModule.forRoot(routes, { preloadingStrategy: NoPreloading })

Solution

1. Step 1: Identify Angular's preloading strategy option

   Angular uses the preloadingStrategy property in router config to set preloading behavior.

2. Step 2: Recognize the correct strategy for all modules

   PreloadAllModules is the built-in strategy to preload all lazy modules after app loads.

3. Final Answer:

   RouterModule.forRoot(routes, { preloadingStrategy: PreloadAllModules }) -> Option A

4. Quick Check:

   PreloadAllModules = preload all lazy modules [OK]

Hint: Use preloadingStrategy: PreloadAllModules to preload all [OK]

Common Mistakes:

• Using 'preload: true' which is invalid
• Confusing NoPreloading with preloading all
• Using lazyLoad option which doesn't exist

3. Given this Angular routing setup:

const routes = [
  { path: 'home', loadChildren: () => import('./home/home.module').then(m => m.HomeModule) },
  { path: 'admin', loadChildren: () => import('./admin/admin.module').then(m => m.AdminModule) }
];

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

What happens after the app loads?

medium

A. Only 'home' module loads eagerly, 'admin' loads on demand

B. 'admin' module preloads, 'home' module does not

C. Neither module preloads; both load on demand

D. Both 'home' and 'admin' modules preload in the background

Solution

1. Step 1: Analyze the preloading strategy used

   The routing uses PreloadAllModules, which preloads all lazy modules after app startup.

2. Step 2: Identify lazy loaded modules

   Both 'home' and 'admin' modules are lazy loaded via loadChildren.

3. Final Answer:

   Both 'home' and 'admin' modules preload in the background -> Option D

4. Quick Check:

   PreloadAllModules preloads all lazy modules [OK]

Hint: PreloadAllModules preloads every lazy module automatically [OK]

Common Mistakes:

• Assuming only first lazy module preloads
• Thinking modules load only on demand with PreloadAllModules
• Confusing eager loading with preloading

4. Identify the error in this Angular routing configuration:

const routes = [
  { path: 'dashboard', loadChildren: './dashboard/dashboard.module#DashboardModule' }
];

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

medium

A. Missing 'pathMatch' property in route

B. Using string syntax for loadChildren is deprecated; should use dynamic import

C. Preloading strategy must be NoPreloading when using lazy loading

D. RouterModule.forRoot should not have a second argument

Solution

1. Step 1: Check loadChildren syntax

   The string syntax ('./dashboard/dashboard.module#DashboardModule') is deprecated in Angular; dynamic import is required.

2. Step 2: Confirm preloading strategy and other options

   Preloading strategy can be used with lazy loading; no error there. 'pathMatch' is optional here.

3. Final Answer:

   Using string syntax for loadChildren is deprecated; should use dynamic import -> Option B

4. Quick Check:

   Use dynamic import() for loadChildren [OK]

Hint: Use dynamic import() syntax for loadChildren [OK]

Common Mistakes:

• Using old string syntax for loadChildren
• Thinking preloading strategy conflicts with lazy loading
• Assuming pathMatch is mandatory for all routes

5. You want to preload only the 'admin' module but not the 'user' module in your Angular app. Which approach correctly implements this custom preloading strategy?

hard

A. Set preloadingStrategy to NoPreloading and preload 'admin' module eagerly

B. Use PreloadAllModules and then lazy load 'user' module manually

C. Create a class implementing PreloadingStrategy that preloads only routes with data.preload = true

D. Mark 'admin' module as eager loaded and 'user' as lazy loaded without preloading

Solution

1. Step 1: Understand custom preloading strategy

   Angular allows creating a class implementing PreloadingStrategy to control which modules preload.

2. Step 2: Use route data property to select modules

   By checking data.preload flag in routes, the strategy can preload only selected modules like 'admin'.

3. Final Answer:

   Create a class implementing PreloadingStrategy that preloads only routes with data.preload = true -> Option C

4. Quick Check:

   Custom strategy uses data.preload flag [OK]

Hint: Use data.preload flag with custom PreloadingStrategy [OK]

Common Mistakes:

• Using PreloadAllModules when selective preload is needed
• Trying to preload modules eagerly without strategy
• Confusing eager loading with preloading