Angular Typescript Interview Question Answers Part 2
Angular Interview Questions – Part 2 (Advanced)
21. What is Change Detection in Angular?
Answer: Change Detection is the mechanism Angular uses to update the UI when data changes.
How it works:
- Angular checks component data
- Updates DOM if data changed
Strategies:
Default→ checks everythingOnPush→ checks only when input changes (better performance)
22. What is OnPush Change Detection?
Answer:
OnPush improves performance by reducing unnecessary checks.
When Angular updates UI:
- Input reference changes
- Event occurs
- Observable emits value
Used in: Large, high-performance applications.
23. What is Lazy Loading in Angular?
Answer: Lazy Loading loads modules only when required, not at app startup.
Benefits:
- Faster initial load
- Better performance
- Optimized memory usage
Example use case: Admin module loads only after login.
24. What is Eager Loading vs Lazy Loading?
Answer:
| Eager Loading | Lazy Loading |
|---|---|
| Loads at startup | Loads on demand |
| Slower startup | Faster startup |
| Simple apps | Large apps |
25. What is RxJS?
Answer: RxJS is a library for reactive programming using Observables.
Why Angular uses RxJS:
- Handles async operations
- Event-based programming
- Stream of data over time
26. Observable vs Promise
Answer:
| Observable | Promise |
|---|---|
| Multiple values | Single value |
| Can cancel | Cannot cancel |
| Lazy execution | Executes immediately |
Interview tip: Angular prefers Observables.
27. What is Subject in RxJS?
Answer: A Subject is both:
- Observable (can be subscribed)
- Observer (can emit values)
Used for:
- Event broadcasting
- Component communication
28. What is BehaviorSubject?
Answer: BehaviorSubject is a Subject that:
- Requires initial value
- Always emits latest value to new subscribers
Use case: User authentication state.
29. What is Async Pipe?
Answer: Async pipe automatically:
- Subscribes to observables
- Unsubscribes on destroy
Benefits:
- Avoids memory leaks
- Cleaner code
30. What is a Memory Leak in Angular?
Answer: Memory leak happens when subscriptions are not unsubscribed.
Common cause: Manual subscriptions without cleanup.
Prevention:
- Async pipe
ngOnDestroytakeUntil
31. What is ngOnDestroy?
Answer: Lifecycle hook used to clean up resources.
Used for:
- Unsubscribing observables
- Clearing timers
32. What is ViewChild?
Answer:
@ViewChild gives access to DOM elements or child components.
Use case: Focus input, call child methods.
33. What is Content Projection?
Answer:
Allows passing HTML content from parent to child using <ng-content>.
Use case: Reusable components like modals, cards.
34. What are Pipes?
Answer: Pipes transform data in templates.
Examples:
dateuppercasecurrency- Custom pipes
35. What is a Custom Pipe?
Answer: A pipe created by developer for custom transformation.
Example use case: Filter search results.
36. What is Angular Guard?
Answer: Guards control route access.
Types:
CanActivateCanDeactivateCanLoad
Use case: Protect routes after login.
37. What is Interceptor?
Answer: HTTP Interceptors intercept API calls.
Used for:
- Adding auth tokens
- Logging
- Error handling
38. What is State Management?
Answer: State management handles shared application data.
Examples:
- User data
- Cart items
- App settings
Popular tools:
- NgRx
- Akita
- Services + RxJS
39. What is NgRx?
Answer: NgRx is a Redux-based state management library for Angular.
Core concepts:
- Store
- Actions
- Reducers
- Effects
Used in: Large enterprise apps.
40. What is Ahead-of-Time (AOT) Compilation?
Answer: AOT compiles Angular code before browser loads it.
Benefits:
- Faster rendering
- Smaller bundle size
- Better security
🔥 Interview Pro Tips
- Always mention performance + scalability
- Explain real-world use cases
- Use keywords: lazy loading, OnPush, RxJS