Why performance tuning matters in Angular - Test Your Understanding

Practice - 5 Tasks

1fill in blank

easy

Complete the code to create a standalone Angular component.

Angular

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

@Component({
  selector: 'app-performance',
  template: `<p>Performance tuning is important!</p>`,
  standalone: [1]
})
export class PerformanceComponent {}

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

Aundefined

Btrue

Cnull

Dfalse

Attempts:

3 left

💡 Hint

Common Mistakes

Setting standalone to false or omitting it.

The standalone property must be set to true to make the component standalone.

2fill in blank

medium

Complete the code to inject the ChangeDetectorRef service.

Angular

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

@Component({
  selector: 'app-tune',
  template: `<p>Change detection example</p>`,
  standalone: true
})
export class TuneComponent {
  constructor(private [1]: ChangeDetectorRef) {}
}

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

Acdr

BchangeRef

Cdetector

Dref

Attempts:

3 left

💡 Hint

Common Mistakes

Using variable names that don't match the injection.

The common variable name for ChangeDetectorRef is cdr, but any valid name works. Here, 'cdr' is the intended name.

3fill in blank

hard

Fix the error in the code to properly use the OnPush change detection strategy.

Angular

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

@Component({
  selector: 'app-fast',
  template: `<p>Fast change detection</p>`,
  changeDetection: [1]
})
export class FastComponent {}

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

AChangeDetectionStrategy.Default

BChangeDetectionStrategy.None

CChangeDetectionStrategy.OnPush

DChangeDetectionStrategy.Fast

Attempts:

3 left

💡 Hint

Common Mistakes

Using Default or invalid strategy names.

To enable performance tuning, use ChangeDetectionStrategy.OnPush which tells Angular to check only when inputs change.

4fill in blank

hard

Fill both blanks to create a signal and update it in Angular 17+.

Angular

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

@Component({
  selector: 'app-signal',
  template: `<button (click)="increment()">Count: {{ count() }}</button>`,
  standalone: true
})
export class SignalComponent {
  count = [1](0);

  increment() {
    this.count([2] + 1);
  }
}

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

Asignal

Bthis.count()

Ccount

Dsignal()

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'count' instead of 'signal' to create signals.

Not calling the signal as a function to get its value.

Use signal(0) to create a signal. To update, call this.count(this.count() + 1).

5fill in blank

hard

Fill all three blanks to create a memo that doubles the count signal value.

Angular

import { Component, signal, computed } from '@angular/core';

@Component({
  selector: 'app-memo',
  template: `<p>Double count: {{ doubleCount() }}</p>`,
  standalone: true
})
export class MemoComponent {
  count = [1](5);
  doubleCount = [2](() => this.count() [3] 2);
}

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

Asignal

B+

C*

Dcomputed

Attempts:

3 left

💡 Hint

Common Mistakes

Using '+' instead of '*' for doubling.

Using 'signal' instead of 'computed' for memo.

Create a signal with signal(5). Use computed to create a memo that multiplies the count by 2.

Practice

1. Why is performance tuning important in Angular applications?

easy

A. It changes the app's color scheme.

B. It adds more features automatically.

C. It reduces the size of the Angular framework.

D. It makes the app faster and improves user experience.

Solution

1. Step 1: Understand the goal of performance tuning

   Performance tuning aims to make apps run faster and smoother for users.

2. Step 2: Identify the effect on user experience

   A faster app improves how users feel and interact with it, making it more enjoyable.

3. Final Answer:

   It makes the app faster and improves user experience. -> Option D

4. Quick Check:

   Performance tuning = better speed and experience [OK]

Hint: Performance tuning improves speed and user experience [OK]

Common Mistakes:

• Thinking it adds new features automatically
• Believing it changes framework size
• Assuming it affects app colors

2. Which Angular feature helps improve performance by reducing change detection checks?

easy

A. Using inline styles

B. Adding more components

C. Using the OnPush change detection strategy

D. Increasing the number of services

Solution

1. Step 1: Identify Angular features for performance

   OnPush strategy tells Angular to check components only when inputs change, reducing work.

2. Step 2: Compare other options

   Adding components or services does not reduce checks; inline styles affect appearance only.

3. Final Answer:

   Using the OnPush change detection strategy -> Option C

4. Quick Check:

   OnPush reduces checks = better performance [OK]

Hint: OnPush reduces unnecessary checks in Angular [OK]

Common Mistakes:

• Confusing inline styles with performance tuning
• Thinking more components improve speed
• Believing more services reduce checks

3. What will be the effect of lazy loading a feature module in Angular?

medium

A. The app loads faster initially by loading modules only when needed.

B. The app loads all modules at once, slowing startup.

C. The app disables routing for the lazy loaded module.

D. The app increases bundle size unnecessarily.

Solution

1. Step 1: Understand lazy loading in Angular

   Lazy loading delays loading a module until the user navigates to it, reducing initial load time.

2. Step 2: Analyze other options

   Loading all modules at once slows startup; disabling routing or increasing bundle size are incorrect effects.

3. Final Answer:

   The app loads faster initially by loading modules only when needed. -> Option A

4. Quick Check:

   Lazy loading = faster initial load [OK]

Hint: Lazy loading delays module load until needed [OK]

Common Mistakes:

• Thinking lazy loading loads all modules upfront
• Assuming routing is disabled
• Believing bundle size grows unnecessarily

4. Given this Angular code snippet, what is the main performance issue?

  @Component({
    selector: 'app-list',
    template: `
      

        {{ item.name }}
      
    `,
    changeDetection: ChangeDetectionStrategy.Default
  })
  export class ListComponent {
    @Input() items: any[] = [];
  }

medium

A. Using Default change detection causes unnecessary checks on every change.

B. The *ngFor directive is not allowed in Angular templates.

C. The component is missing a selector.

D. The items input should be a string, not an array.

Solution

1. Step 1: Identify change detection strategy

   The component uses Default strategy, which runs checks on all changes, even if items don't change.

2. Step 2: Understand impact on performance

   This causes Angular to check the component often, slowing performance especially with large lists.

3. Final Answer:

   Using Default change detection causes unnecessary checks on every change. -> Option A

4. Quick Check:

   Default strategy = more checks, slower performance [OK]

Hint: Default change detection runs often, slowing app [OK]

Common Mistakes:

• Thinking *ngFor is invalid syntax
• Missing the selector is not the issue here
• Assuming input type is wrong

5. You want to improve an Angular app's performance by minimizing change detection and loading only needed code. Which combination is best?

hard

A. Use OnPush change detection and load all modules eagerly.

B. Use OnPush change detection and lazy load feature modules.

C. Use Default change detection and load all modules eagerly.

D. Use Default change detection and lazy load feature modules.

Solution

1. Step 1: Choose change detection strategy

   OnPush reduces unnecessary checks by running only when inputs change, improving speed.

2. Step 2: Choose module loading strategy

   Lazy loading delays loading modules until needed, reducing initial load time and memory use.

3. Step 3: Combine strategies for best performance

   Using both OnPush and lazy loading together maximizes performance benefits.

4. Final Answer:

   Use OnPush change detection and lazy load feature modules. -> Option B

5. Quick Check:

   OnPush + lazy loading = best performance [OK]

Hint: Combine OnPush and lazy loading for best speed [OK]

Common Mistakes:

• Using Default detection reduces speed
• Loading all modules eagerly slows startup
• Mixing strategies reduces benefits