10 Angular 8+ Interview Questions and Answers

Angular 8+ is a powerful and widely-used framework for building dynamic web applications. Known for its robust features, such as two-way data binding, dependency injection, and a modular architecture, Angular simplifies the development process and enhances performance. Its strong community support and comprehensive documentation make it a go-to choice for developers aiming to create scalable and maintainable applications.

This article offers a curated selection of interview questions designed to test your knowledge and proficiency in Angular 8+. By working through these questions, you will gain a deeper understanding of key concepts and be better prepared to demonstrate your expertise in a technical interview setting.

Angular 8+ Interview Questions and Answers

1. Explain the purpose and usage of Angular’s component lifecycle hooks.

Angular’s component lifecycle hooks allow developers to execute custom logic during specific phases of a component’s lifecycle, from creation to destruction. Common hooks include:

• ngOnInit: Used for initializing data and setting up the component.
• ngOnChanges: Reacts to changes in input properties.
• ngDoCheck: Allows for custom change detection logic.
• ngAfterViewInit: Useful for DOM manipulation or initializing third-party libraries.
• ngOnDestroy: Used for cleanup tasks like unsubscribing from observables.

Example:

import { Component, OnInit, OnChanges, DoCheck, AfterViewInit, OnDestroy, Input } from '@angular/core';

@Component({
  selector: 'app-lifecycle-demo',
  template: '<p>{{data}}</p>'
})
export class LifecycleDemoComponent implements OnInit, OnChanges, DoCheck, AfterViewInit, OnDestroy {
  @Input() data: string;

  ngOnInit() {
    console.log('ngOnInit called');
  }

  ngOnChanges() {
    console.log('ngOnChanges called');
  }

  ngDoCheck() {
    console.log('ngDoCheck called');
  }

  ngAfterViewInit() {
    console.log('ngAfterViewInit called');
  }

  ngOnDestroy() {
    console.log('ngOnDestroy called');
  }
}

2. How does dependency injection work in Angular, and why is it important?

Dependency injection in Angular supplies a class with its dependencies from an external source via Angular’s injector, which maintains a container of dependency instances. You define providers for dependencies in the module, component, or service metadata. The injector uses these providers to create instances and inject them where needed.

Example:

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

@Injectable({
  providedIn: 'root',
})
export class DataService {
  getData() {
    return 'Data from service';
  }
}

import { Component } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-root',
  template: '<h1>{{ data }}</h1>',
})
export class AppComponent {
  data: string;

  constructor(private dataService: DataService) {
    this.data = this.dataService.getData();
  }
}

3. Explain how state management is handled using NgRx in Angular applications.

NgRx is a state management library for Angular applications based on the Redux pattern, providing a predictable way to manage application state. Core concepts include actions, reducers, selectors, and effects.

Actions send data from the application to the store. Reducers specify how the state changes in response to actions. Selectors obtain slices of the state. Effects handle side effects, such as asynchronous operations.

Example:

// actions.ts
import { createAction, props } from '@ngrx/store';

export const loadItems = createAction('[Item List] Load Items');
export const loadItemsSuccess = createAction(
  '[Item List] Load Items Success',
  props<{ items: any[] }>()
);

// reducer.ts
import { createReducer, on } from '@ngrx/store';
import { loadItems, loadItemsSuccess } from './actions';

export const initialState = {
  items: [],
  loading: false
};

const _itemReducer = createReducer(
  initialState,
  on(loadItems, state => ({ ...state, loading: true })),
  on(loadItemsSuccess, (state, { items }) => ({ ...state, items, loading: false }))
);

export function itemReducer(state, action) {
  return _itemReducer(state, action);
}

// selectors.ts
import { createSelector } from '@ngrx/store';

export const selectItems = state => state.items;
export const selectLoading = state => state.loading;

4. Describe how to implement an HTTP interceptor in Angular and provide a use case.

An HTTP interceptor in Angular is a service that implements the HttpInterceptor interface, allowing interception of HTTP requests and responses for operations like adding headers or handling errors. Interceptors are useful for adding authentication tokens to requests or for global error handling.

Example:

import { Injectable } from '@angular/core';
import { HttpInterceptor, HttpRequest, HttpHandler, HttpEvent } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable()
export class AuthInterceptor implements HttpInterceptor {
  intercept(req: HttpRequest<any>, next: HttpHandler): Observable<HttpEvent<any>> {
    const authToken = 'your-auth-token';
    const authReq = req.clone({
      headers: req.headers.set('Authorization', `Bearer ${authToken}`)
    });
    return next.handle(authReq);
  }
}

To use this interceptor, provide it in your app module:

import { HTTP_INTERCEPTORS } from '@angular/common/http';
import { AuthInterceptor } from './auth.interceptor';

@NgModule({
  providers: [
    { provide: HTTP_INTERCEPTORS, useClass: AuthInterceptor, multi: true }
  ]
})
export class AppModule {}

5. Explain the process of dynamically loading a component in Angular.

Dynamically loading a component in Angular involves using a placeholder in your template, typically with ng-template, and Angular’s ComponentFactoryResolver to create and insert the component into the view.

Example:

import { Component, ComponentFactoryResolver, ViewChild, ViewContainerRef } from '@angular/core';

@Component({
  selector: 'app-dynamic-loader',
  template: `<ng-template #dynamicComponent></ng-template>`
})
export class DynamicLoaderComponent {
  @ViewChild('dynamicComponent', { read: ViewContainerRef, static: true }) container: ViewContainerRef;

  constructor(private resolver: ComponentFactoryResolver) {}

  loadComponent(component: any) {
    const factory = this.resolver.resolveComponentFactory(component);
    this.container.clear();
    this.container.createComponent(factory);
  }
}

6. Discuss various techniques to optimize the performance of an Angular application.

Optimizing Angular application performance involves several techniques:

• Lazy Loading: Load modules only when needed to reduce initial load time.
• Change Detection Strategy: Use the OnPush strategy to reduce checks.
• Ahead-of-Time (AOT) Compilation: Compiles code during the build phase to reduce runtime work.
• Tree Shaking: Removes unused code to reduce bundle size.
• Angular CLI for Production Builds: Ensures optimizations like minification and tree shaking.
• Caching and Service Workers: Reduce network resource fetching.
• Optimizing Template Expressions: Avoid complex logic in templates.
• Using Pure Pipes: Recalculate only when input changes.

7. What is Angular Universal, and what are its benefits?

Angular Universal is a server-side rendering (SSR) solution for Angular applications, improving initial load time and SEO by rendering the application on the server.

Benefits include:

• Improved Performance: Faster perceived load time by rendering the initial view on the server.
• Better SEO: Easier indexing by search engines with server-rendered HTML.
• Enhanced User Experience: Faster load times for users with slower connections.
• Social Media Sharing: Accurate preview content with server-rendered HTML.

8. Describe the role of Observables and RxJS in Angular applications.

In Angular, Observables handle asynchronous data streams, such as HTTP requests and user input events. RxJS provides operators to manipulate these streams, facilitating complex asynchronous operations.

Example:

import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Component({
  selector: 'app-data',
  template: `<div *ngIf="data">{{ data }}</div>`
})
export class DataComponent implements OnInit {
  data: any;

  constructor(private http: HttpClient) {}

  ngOnInit() {
    this.getData().subscribe(response => {
      this.data = response;
    });
  }

  getData(): Observable<any> {
    return this.http.get('https://api.example.com/data');
  }
}

9. What is Angular Ivy, and what are its advantages over the previous rendering engine?

Angular Ivy, introduced in Angular 8, is the new rendering engine that replaces the older View Engine. It offers several improvements:

• Smaller Bundle Sizes: Generates smaller JavaScript bundles for faster load times.
• Faster Compilation: Improves build and rebuild times.
• Better Debugging: Provides more readable error messages.
• Improved Type Checking: Enhances type checking to catch errors at compile time.
• Lazy Loading: Supports more efficient lazy loading.
• Backward Compatibility: Designed to be compatible with existing applications.

10. How can Angular Material be used to enhance the UI of an Angular application?

Angular Material enhances the UI of an Angular application with pre-built components that follow Material Design principles, ensuring a consistent and modern look.

To use Angular Material, install it via npm and import the necessary modules:

// Install Angular Material
// npm install @angular/material @angular/cdk @angular/animations

// Import Angular Material modules in your app.module.ts
import { MatButtonModule } from '@angular/material/button';
import { MatToolbarModule } from '@angular/material/toolbar';
import { BrowserAnimationsModule } from '@angular/platform-browser/animations';

@NgModule({
  declarations: [
    // your components
  ],
  imports: [
    BrowserAnimationsModule,
    MatButtonModule,
    MatToolbarModule,
    // other modules
  ],
  providers: [],
  bootstrap: [AppComponent]
})
export class AppModule { }

// Use Angular Material components in your template
// app.component.html
<mat-toolbar color="primary">
  <span>My Application</span>
</mat-toolbar>

<button mat-raised-button color="accent">Click Me</button>