Lazy loading standalone components in Angular - Mini Project: Build & Apply

Lazy Loading Standalone Components in Angular

📖 Scenario: You are building a simple Angular app that shows different messages on demand. To keep the app fast, you want to load the message components only when the user asks for them.

🎯 Goal: Build an Angular app that lazy loads two standalone components: WelcomeComponent and GoodbyeComponent. The app should load these components only when the user clicks their buttons.

📋 What You'll Learn

Create two standalone components: WelcomeComponent and GoodbyeComponent

Create a main AppComponent with buttons to load each component

Use Angular's loadComponent method to lazy load the components on button click

Display the loaded component inside a container in AppComponent

💡 Why This Matters

🌍 Real World

Lazy loading standalone components helps keep Angular apps fast by loading only what the user needs when they need it.

💼 Career

Understanding lazy loading is important for building scalable Angular applications that perform well and provide a good user experience.

1

Create the standalone components

Create two standalone components named WelcomeComponent and GoodbyeComponent. Each should have a simple template: WelcomeComponent displays "Welcome to the app!" and GoodbyeComponent displays "Goodbye! See you soon."

Angular

# Create WelcomeComponent and GoodbyeComponent as standalone components
# Your code here

Hint

Use @Component decorator with standalone: true and simple templates for each component.

2

Set up the AppComponent with buttons and container

Create a standalone AppComponent with two buttons labeled "Show Welcome" and "Show Goodbye". Add a container element with a template reference variable #container where the lazy loaded components will appear.

Angular

import { Component } from '@angular/core';

@Component({
  selector: 'app-welcome',
  standalone: true,
  template: `Welcome to the app!`
})
export class WelcomeComponent {}

@Component({
  selector: 'app-goodbye',
  standalone: true,
  template: `Goodbye! See you soon.`
})
export class GoodbyeComponent {}

@Component({
  selector: 'app-root',
  standalone: true,
  template: `
    Show Welcome
    Show Goodbye
    
  `
})
export class AppComponent {}

# Add buttons and container with #container reference
# Your code here

Hint

Use @ViewChild to get the container reference and add buttons with click handlers.

3

Implement lazy loading logic for components

In AppComponent, implement the methods showWelcome() and showGoodbye(). Use this.container.clear() to clear the container, then use this.container.loadComponent() with dynamic imports to lazy load WelcomeComponent and GoodbyeComponent respectively.

Angular

  showWelcome() {
    this.container.clear();
    this.container.loadComponent(() => import('./welcome.component').then(m => m.WelcomeComponent));
  }
  showGoodbye() {
    this.container.clear();
    this.container.loadComponent(() => import('./goodbye.component').then(m => m.GoodbyeComponent));
  }
# Add main.ts bootstrap code with BrowserModule and AppComponent

Hint

Use dynamic import() inside loadComponent() to lazy load each component.

4

Complete the app with bootstrap and imports

Add the necessary imports and bootstrap code to run the Angular app with AppComponent as the root. Import BrowserModule and bootstrap AppComponent in main.ts.

Angular

Hint

Use bootstrapApplication(AppComponent) to start the app and import BrowserModule in AppComponent.

Practice

1. What is the main benefit of lazy loading standalone components in Angular?

easy

A. It bundles all components into a single file

B. It automatically updates components without user action

C. It disables component rendering on mobile devices

D. It improves app speed by loading components only when needed

Solution

1. Step 1: Understand lazy loading purpose

   Lazy loading delays loading parts of the app until they are needed, reducing initial load time.

2. Step 2: Connect lazy loading to standalone components

   Standalone components can be lazy loaded to improve app speed by not loading them upfront.

3. Final Answer:

   It improves app speed by loading components only when needed -> Option D

4. Quick Check:

   Lazy loading = improves speed [OK]

Hint: Lazy loading means load only when needed [OK]

Common Mistakes:

• Thinking lazy loading bundles all components together
• Confusing lazy loading with automatic updates
• Believing lazy loading disables components on devices

2. Which syntax correctly lazy loads a standalone component in Angular routing?

easy

A. { path: 'home', loadComponent: () => import('./home.component').then(m => m.HomeComponent) }

B. { path: 'home', component: () => import('./home.component').then(m => m.HomeComponent) }

C. { path: 'home', loadChildren: () => import('./home.component').then(m => m.HomeComponent) }

D. { path: 'home', loadModule: () => import('./home.component').then(m => m.HomeComponent) }

Solution

1. Step 1: Identify correct property for lazy loading standalone components

   Angular uses loadComponent to lazy load standalone components in routes.

2. Step 2: Check syntax correctness

   { path: 'home', loadComponent: () => import('./home.component').then(m => m.HomeComponent) } uses loadComponent with dynamic import and then returns the component class, which is correct.

3. Final Answer:

   { path: 'home', loadComponent: () => import('./home.component').then(m => m.HomeComponent) } -> Option A

4. Quick Check:

   Lazy load standalone = loadComponent [OK]

Hint: Use loadComponent with dynamic import for standalone lazy loading [OK]

Common Mistakes:

• Using component property instead of loadComponent
• Using loadChildren for components instead of modules
• Using non-existent loadModule property

3. Given this route config, what happens when navigating to '/dashboard'?

{ path: 'dashboard', loadComponent: () => import('./dashboard.component').then(m => m.DashboardComponent) }

medium

A. The DashboardComponent is loaded immediately when the app starts

B. The DashboardComponent is loaded only when '/dashboard' is visited

C. The DashboardComponent is never loaded

D. The app throws a runtime error due to missing component

Solution

1. Step 1: Understand loadComponent behavior

   Using loadComponent with dynamic import delays loading the component until the route is accessed.

2. Step 2: Apply to '/dashboard' route

   The DashboardComponent will load only when the user navigates to '/dashboard', not before.

3. Final Answer:

   The DashboardComponent is loaded only when '/dashboard' is visited -> Option B

4. Quick Check:

   loadComponent = lazy load on route visit [OK]

Hint: loadComponent loads component on route visit only [OK]

Common Mistakes:

• Assuming component loads at app start
• Thinking component never loads
• Expecting runtime error without import

4. Identify the error in this route config for lazy loading a standalone component:

{ path: 'profile', loadComponent: import('./profile.component').then(m => m.ProfileComponent) }

medium

A. Missing arrow function wrapping the import call

B. Using loadComponent instead of component property

C. Incorrect path string format

D. Missing import statement at the top of the file

Solution

1. Step 1: Check loadComponent syntax

   The loadComponent property must be a function returning a Promise, so it needs an arrow function wrapping the import.

2. Step 2: Identify missing arrow function

   The code calls import directly without wrapping in a function, causing the component to load eagerly or a runtime error when the router tries to invoke it.

3. Final Answer:

   Missing arrow function wrapping the import call -> Option A

4. Quick Check:

   loadComponent requires () => import(...) [OK]

Hint: Wrap import in arrow function for loadComponent [OK]

Common Mistakes:

• Calling import directly without function
• Confusing loadComponent with component property
• Thinking import must be at file top

5. You want to lazy load two standalone components, AdminComponent and UserComponent, under routes '/admin' and '/user'. Which is the best way to configure the routes to optimize initial load time?

hard

A. Import both components eagerly and assign them to routes directly

B. Use loadChildren to lazy load a module containing both components

C. Use loadComponent with dynamic imports for both routes separately

D. Combine both components into one and lazy load that single component

Solution

1. Step 1: Understand lazy loading standalone components

   Using loadComponent with dynamic imports allows each component to load only when its route is visited, reducing initial load.

2. Step 2: Compare options for multiple components

   Use loadComponent with dynamic imports for both routes separately loads each component lazily and separately, optimizing load time better than eager loading or bundling.

3. Final Answer:

   Use loadComponent with dynamic imports for both routes separately -> Option C

4. Quick Check:

   Separate loadComponent calls = best lazy loading [OK]

Hint: Lazy load each standalone component separately with loadComponent [OK]

Common Mistakes:

• Eagerly importing components defeats lazy loading
• Using loadChildren for standalone components unnecessarily
• Combining components increases initial load size