Angular Quiz ( Advance ) - All Questions

This advanced Angular quiz is designed for senior frontend developers and engineers preparing for high-level interviews. It focuses on Angular internals, change detection mechanics, performance optimization, RxJS patterns, architecture decisions, and real-world production scenarios.

Question 1: Why does Angular use Zone.js?

For routing
For HTTP interception
To trigger change detection on async tasks
To manage dependency injection

Explanation: Zone.js tracks async operations to trigger change detection.

Question 2: What is the main drawback of Default change detection strategy?

Hard to debug
Excessive change detection cycles
No async support
Poor routing

Explanation: Default strategy checks all components frequently.

Question 3: When does OnPush change detection run?

On every async event
Only on route change
When input references change or events occur
Only manually

Explanation: OnPush runs on reference changes or explicit triggers.

Question 4: Which scenario can break OnPush change detection?

Immutable data
Async pipes
Mutating object properties
Using Observables

Explanation: Mutating objects does not change references.

Question 5: What does ChangeDetectorRef.markForCheck() do?

Destroys component
Forces full app check
Marks component for next check cycle
Detaches change detector

Explanation: It schedules the component for checking.

Question 6: What is the purpose of ChangeDetectorRef.detach()?

Disable routing
Stop change detection for component subtree
Destroy component
Pause Zone.js

Explanation: Detached components are skipped in change detection.

Question 7: Which RxJS operator cancels previous HTTP requests?

mergeMap
concatMap
switchMap
exhaustMap

Explanation: switchMap cancels previous inner subscriptions.

Question 8: Which RxJS operator ensures sequential execution?

mergeMap
switchMap
exhaustMap
concatMap

Explanation: concatMap waits for previous completion.

Question 9: Which operator ignores new emissions while one is active?

switchMap
mergeMap
exhaustMap
concatMap

Explanation: exhaustMap ignores new values until completion.

Question 10: Why is unsubscribe important in Angular?

Avoid syntax errors
Prevent memory leaks
Improve routing speed
Reduce bundle size

Explanation: Unsubscribed observables prevent memory leaks.

Question 11: Which Angular feature handles automatic unsubscription?

Subject
takeUntil
Async pipe
BehaviorSubject

Explanation: Async pipe manages subscriptions automatically.

Question 12: What problem does takeUntil solve?

Error handling
Memory leaks
Race conditions
Routing conflicts

Explanation: takeUntil completes streams on destroy.

Question 13: Which Angular concept enforces singleton services?

Modules
Components
Dependency Injection
Pipes

Explanation: DI ensures controlled service instances.

Question 14: Why is providedIn: 'root' preferred?

Lazy loading
Tree-shakable services
Faster routing
Scoped providers

Explanation: It enables tree-shaking for unused services.

Question 15: What causes multiple instances of a service?

Providing service in root
Providing service in component providers
Using lazy loading
Using HttpClient

Explanation: Component-level providers create new instances.

Question 16: What is the risk of subscribing inside subscribe?

Syntax errors
Callback hell and leaks
Broken change detection
Routing issues

Explanation: Nested subscriptions are hard to manage.

Question 17: Which Angular feature supports state management?

Services with Observables
Templates
Directives
Pipes

Explanation: Services + Observables manage shared state.

Question 18: Which library is commonly used for large-scale state management?

Zone.js
NgRx
RxDOM
Lodash

Explanation: NgRx provides Redux-style state management.

Question 19: What is the main drawback of NgRx?

Performance
Boilerplate code
Learning TypeScript
Routing issues

Explanation: NgRx introduces significant boilerplate.

Question 20: What is a selector in NgRx?

Action creator
Reducer function
Derived state reader
Effect handler

Explanation: Selectors compute derived state.

Question 21: Why are Effects used in NgRx?

Sync state updates
Handle side effects
Render components
Validate forms

Explanation: Effects manage async side effects.

Question 22: Which Angular feature improves initial load time?

Change detection
Lazy loading modules
Two-way binding
Zone.js

Explanation: Lazy loading reduces initial bundle size.

Question 23: What is preloading strategy used for?

Eager loading
Background loading of lazy modules
Caching templates
Optimizing change detection

Explanation: Preloading loads lazy modules after bootstrap.

Question 24: Which preloading strategy loads all modules?

NoPreloading
SelectivePreload
PreloadAllModules
ImmediateLoad

Explanation: PreloadAllModules loads all lazy modules.

Question 25: What is AOT compilation?

Runtime compilation
Template pre-compilation
Lazy rendering
Dynamic injection

Explanation: AOT compiles templates at build time.

Question 26: Why is AOT preferred in production?

Faster builds
Smaller bundles and faster rendering
Better debugging
Simpler syntax

Explanation: AOT improves performance and security.

Question 27: What security benefit does AOT provide?

XSS prevention
CSRF protection
No runtime template injection
Auth validation

Explanation: Templates are not compiled at runtime.

Question 28: Which Angular feature sanitizes HTML automatically?

Renderer2
DomSanitizer
HttpClient
Zone.js

Explanation: DomSanitizer prevents unsafe HTML execution.

Question 29: Why should bypassSecurityTrustHtml be used cautiously?

Performance cost
Memory leaks
XSS risk
Routing errors

Explanation: It disables Angular security checks.

Question 30: Which lifecycle hook is best for DOM measurements?

ngOnInit
ngAfterViewInit
ngOnChanges
ngDoCheck

Explanation: View is fully initialized at this stage.

Question 31: What is content projection mainly used for?

Routing
Reusable layout components
Lazy loading
State sharing

Explanation: ng-content enables flexible component layouts.

Question 32: Which Angular API allows direct DOM manipulation safely?

ElementRef
Renderer2
document
window

Explanation: Renderer2 abstracts DOM access safely.

Question 33: Why is direct ElementRef usage discouraged?

Syntax errors
Security risks
Performance loss
Change detection issues

Explanation: It may expose the app to XSS.

Question 34: Which technique reduces bundle size most effectively?

Two-way binding
Tree shaking
Change detection
Zone.js

Explanation: Tree shaking removes unused code.

Question 35: What is differential loading?

Multiple builds for browsers
Lazy loading technique
CSS optimization
SSR strategy

Explanation: It serves modern or legacy bundles based on browser.

Question 36: Which Angular feature enables server-side rendering?

Angular Universal
Zone.js
Renderer2
AOT

Explanation: Angular Universal enables SSR.

Question 37: What is the main benefit of SSR?

Smaller bundles
Better SEO and faster first paint
Simpler architecture
Reduced memory usage

Explanation: SSR improves SEO and perceived performance.

Question 38: Which issue commonly appears with SSR?

Routing errors
Browser-only APIs usage
Change detection failure
Form validation

Explanation: window/document are unavailable on server.

Question 39: Why should ChangeDetectionStrategy.OnPush be combined with immutability?

Cleaner syntax
Predictable updates
Smaller bundles
Better routing

Explanation: Immutable data ensures reference changes.

Question 40: What does trackBy primarily reduce?

Security risks
Memory leaks
DOM re-rendering
API calls

Explanation: trackBy minimizes DOM updates.

Question 41: Which Angular practice improves large-scale maintainability?

Global services only
Feature modules with clear boundaries
Inline templates
Two-way binding everywhere

Explanation: Feature modules improve separation of concerns.

Question 42: Why are long-running subscriptions dangerous?

Slow UI
Memory leaks
Routing failures
Template errors

Explanation: They retain memory unnecessarily.

Question 43: Which Angular concept helps build scalable architectures?

Direct DOM access
Reactive programming with RxJS
Two-way binding
Global state

Explanation: Reactive patterns scale well.

Question 44: What is the biggest architectural advantage of Angular?

Minimal setup
Strong structure and tooling
Lightweight runtime
Simple syntax

Explanation: Angular enforces scalable structure.

Question 45: Which mistake most commonly causes Angular performance issues?

Using pipes
Excessive default change detection
Lazy loading modules
Using Observables

Explanation: Default change detection can be expensive.

Question 46: What is the ultimate goal of Angular architecture?

Fast scripting
Scalable enterprise applications
Minimal bundle size
Simple DOM manipulation

Explanation: Angular is designed for large-scale apps.

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