Angular Interview Questions
35 questions with detailed answers
Question:
What is Angular and what are its key features?
Answer:
Angular is a TypeScript-based open-source web application framework developed by Google. Key features include: Component-based architecture, Two-way data binding, Dependency injection, Directives and pipes, Routing and navigation, RxJS for reactive programming, CLI for development workflow, Cross-platform development support.
Question:
What are the main differences between Angular and AngularJS?
Answer:
Key differences: Language (Angular uses TypeScript, AngularJS uses JavaScript), Architecture (Angular is component-based, AngularJS is MVC-based), Mobile Support (Angular has better mobile support), Performance (Angular is faster with better change detection), CLI (Angular has powerful CLI tools).
Question:
What are Angular components and how do you create them?
Answer:
Components are the basic building blocks of Angular applications. They control a patch of screen called a view. Create using: @Component({ selector: "app-hello", template: "
{{title}}
" }) export class HelloComponent { title = "Hello World"; }. CLI: ng generate component component-nameQuestion:
Explain the different types of data binding in Angular.
Answer:
Angular supports four types: 1. Interpolation {{value}} - One-way from component to view, 2. Property Binding [property]="value" - One-way from component to view, 3. Event Binding (event)="handler()" - One-way from view to component, 4. Two-way Binding [(ngModel)]="property" - Bidirectional
Question:
What are Angular directives and their types?
Answer:
Directives are classes that add additional behavior to elements. Types: 1. Component Directives (Components with templates), 2. Structural Directives (*ngIf, *ngFor, *ngSwitch), 3. Attribute Directives (ngClass, ngStyle)
Question:
What is Angular CLI and its common commands?
Answer:
Angular CLI is a command-line interface tool. Commands: ng new (create project), ng serve (dev server), ng generate component (create component), ng build (production build), ng test (run tests), ng e2e (end-to-end tests)
Question:
What are Angular services and dependency injection?
Answer:
Services are singleton objects providing functionality across the application. DI is a design pattern where dependencies are provided to a class. Example: @Injectable({ providedIn: "root" }) export class DataService { getData() { return this.http.get("/api/data"); } }
Question:
Explain Angular component lifecycle hooks.
Answer:
Lifecycle hooks: ngOnInit (Initialize after constructor), ngOnChanges (Input changes), ngDoCheck (Custom change detection), ngAfterContentInit (After content projection), ngAfterViewInit (After view init), ngOnDestroy (Cleanup)
Question:
How does routing work in Angular?
Answer:
Angular Router enables navigation between views. Setup: const routes: Routes = [{ path: "home", component: HomeComponent }]; @NgModule({ imports: [RouterModule.forRoot(routes)] }). Template:
Question:
What are Angular pipes and how do you create custom pipes?
Answer:
Pipes transform displayed values without changing original data. Built-in: date, currency, uppercase. Custom: @Pipe({name: "exponential"}) export class ExponentialPipe implements PipeTransform { transform(value: number, exponent = 1): number { return Math.pow(value, exponent); } }
Question:
Explain template-driven vs reactive forms in Angular.
Answer:
Template-driven: Form logic in template, uses ngModel, suitable for simple forms. Reactive: Form logic in component, uses FormControl/FormGroup, better for complex validation. Example: this.userForm = this.fb.group({ name: ["", Validators.required] });
Question:
What are Angular modules and their purpose?
Answer:
NgModules organize related components, directives, pipes, and services. Types: Root Module (AppModule), Feature Modules, Shared Modules, Core Modules. Example: @NgModule({ declarations: [AppComponent], imports: [BrowserModule], providers: [DataService] })
Question:
What are Angular Elements and how to create custom elements?
Answer:
Angular Elements allows you to create custom elements (Web Components) from Angular components. Example: import { createCustomElement } from "@angular/elements"; const PopupElement = createCustomElement(PopupComponent, { injector }); customElements.define("popup-element", PopupElement);
Question:
How do you implement dynamic component loading?
Answer:
Use ViewContainerRef and createComponent to load components dynamically. Example: @ViewChild("container", { read: ViewContainerRef }) container; loadComponent() { this.container.clear(); const componentRef = this.container.createComponent(DynamicComponent); }
Question:
What is Angular Ivy renderer and its benefits?
Answer:
Ivy is Angular rendering engine (default since v9). Benefits: Smaller bundle sizes, Faster builds, Better tree-shaking, Improved debugging, Dynamic imports for lazy loading, Better i18n support.
Question:
How do you optimize Angular application performance?
Answer:
Performance optimization techniques: OnPush change detection strategy, Lazy loading modules, TrackBy functions in *ngFor, Async pipe for observables, Preloading strategies, Bundle analysis and tree shaking, Service workers for caching.
Question:
What are Angular Schematics and how to create them?
Answer:
Schematics are templates that generate or modify code. Create: import { Rule, Tree } from "@angular-devkit/schematics"; export function mySchematic(): Rule { return (tree: Tree) => { tree.create("hello.txt", "Hello World!"); return tree; }; }
Question:
Explain Angular change detection and OnPush strategy.
Answer:
Change detection checks for data changes and updates DOM. Default: Checks all components on every change. OnPush: Only checks when input properties change, events occur, or observables emit. Use @Component({ changeDetection: ChangeDetectionStrategy.OnPush })
Question:
How are RxJS Observables used in Angular?
Answer:
RxJS provides reactive programming with Observables for async data streams. Usage: HTTP requests (this.http.get("/api/data").subscribe()), Form changes (this.form.valueChanges.pipe(debounceTime(300))), Custom observables (const timer$ = interval(1000))
Question:
What are Angular route guards and their types?
Answer:
Route guards control navigation. Types: CanActivate (Can route be activated?), CanDeactivate (Can user leave?), CanLoad (Can module be loaded?), Resolve (Pre-fetch data). Example: @Injectable() export class AuthGuard implements CanActivate { canActivate(): boolean { return this.authService.isAuthenticated(); } }
Question:
Explain content projection in Angular.
Answer:
Content projection allows inserting content from parent into child component template using ng-content. Example: Child template:
Projected content
Question:
What is the difference between ViewChild and ContentChild?
Answer:
ViewChild accesses child components/elements in template, ContentChild accesses projected content. ViewChild works with template elements, ContentChild works with ng-content projected elements.
Question:
How do you create and use HTTP interceptors?
Answer:
Implement HttpInterceptor interface to intercept HTTP requests/responses. Example: @Injectable() export class AuthInterceptor implements HttpInterceptor { intercept(req, next) { const authReq = req.clone({ headers: req.headers.set("Authorization", "Bearer " + token) }); return next.handle(authReq); } }
Question:
What is Angular Universal and Server-Side Rendering?
Answer:
Angular Universal enables server-side rendering for better SEO and initial load performance. Benefits: Faster initial page load, Better SEO, Social media preview support. Setup: ng add @nguniversal/express-engine
Question:
How do you implement custom validators in reactive forms?
Answer:
Create functions returning ValidationErrors or null. Example: function emailValidator(control: AbstractControl): ValidationErrors | null { const email = control.value; if (!email || email.includes("@")) return null; return { invalidEmail: true }; }
Question:
Explain Angular security best practices.
Answer:
Angular security features: XSS prevention via sanitization, CSRF protection with HttpClientXsrfModule, Content Security Policy (CSP) support. Best practices: Use HTTPS, Validate inputs, Avoid innerHTML with user data, Regular security audits.
Question:
What are Angular Standalone Components (v14+)?
Answer:
Standalone components do not need NgModules. Example: @Component({ selector: "app-standalone", standalone: true, imports: [CommonModule, FormsModule], template: "
Standalone component
" }) export class StandaloneComponent {}Question:
How do you implement state management with NgRx?
Answer:
NgRx uses Redux pattern with Actions, Reducers, Effects, and Selectors. Example: export const loadUsers = createAction("[User] Load Users"); const userReducer = createReducer(initialState, on(loadUsers, state => ({ ...state, loading: true })));
Question:
What is Angular Universal and its implementation?
Answer:
Angular Universal enables server-side rendering for better SEO and performance. Setup: ng add @nguniversal/express-engine, npm run build:ssr, npm run serve:ssr. Benefits: Faster initial load, Better SEO, Social media previews.
Question:
How do you implement micro frontends with Angular?
Answer:
Micro frontend approaches: Module Federation (Webpack 5), Angular Elements, Single-SPA framework, Iframe-based solutions. Benefits: Independent deployment, technology diversity, team autonomy.
Question:
Explain Angular Signals (v16+) and their benefits.
Answer:
Signals provide fine-grained reactivity. Example: count = signal(0); doubleCount = computed(() => this.count() * 2); increment() { this.count.update(value => value + 1); } Benefits: Better performance, simpler mental model.
Question:
How do you implement custom decorators in Angular?
Answer:
Create functions that modify class behavior. Example: export function LogMethod(target: any, propertyName: string, descriptor: PropertyDescriptor) { const method = descriptor.value; descriptor.value = function (...args: any[]) { console.log("Calling ${propertyName}"); return method.apply(this, args); }; }
Question:
What is Zone.js and NgZone in Angular?
Answer:
Zone.js patches asynchronous operations to trigger change detection. NgZone methods: runOutsideAngular(() => { /* no change detection */ }), run(() => { /* triggers change detection */ }). Used for performance optimization.
Question:
How do you implement Angular animations?
Answer:
Use @angular/animations with trigger, state, style, animate. Example: @Component({ animations: [trigger("slideIn", [transition(":enter", [style({ transform: "translateX(-100%)" }), animate("300ms ease-in")])])] })
Question:
What are Angular testing strategies and best practices?
Answer:
Testing strategies: Unit tests with TestBed, Component testing with fixtures, Service testing with mocks, HTTP testing with HttpClientTestingModule, E2E testing with Cypress/Protractor. Use spies, async testing, and proper mocking.