Angular Interview Questions for Mid-Level Developers – 2024

Angular Interview Questions for Mid-Level Developers – 2024

Core Concepts

1. Explain the key components of the Angular architecture (Components, Templates, Services, NgModules, etc.) and how they interact.
2. Describe the purpose of data binding in Angular and its different types (one-way, two-way).
3. Explain the concept of dependency injection in Angular and its benefits.
4. Differentiate between routing and navigation in Angular and provide examples.
5. Describe the various lifecycle hooks available in Angular components and their functionalities.

Explain the key components of the Angular architecture (Components, Templates, Services, NgModules, etc.) and how they interact.

Components:

Angular applications are built using components, which are the fundamental building blocks. A component consists of a TypeScript class that encapsulates the component’s behavior and properties, an HTML template that defines the component’s view, and a CSS stylesheet for styling.

// app.component.ts
import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  title = 'My Angular App';
}

Templates:

Templates define the view of a component and are written in HTML with Angular-specific syntax. They provide the structure for the user interface and can include data binding expressions to dynamically display component properties.

<!-- app.component.html -->
<h1>{{ title }}</h1>

Services:

Services are reusable components that encapsulate business logic and can be injected into components or other services. They promote code modularity and maintainability.

// data.service.ts
import { Injectable } from '@angular/core';

@Injectable({
  providedIn: 'root'
})
export class DataService {
  getData(): string {
    return 'Hello from DataService';
  }
}

NgModules:

NgModules are containers for organizing and managing related components, directives, pipes, and services in Angular applications. They define a compilation context for components.

// app.module.ts
import { NgModule } from '@angular/core';
import { AppComponent } from './app.component';
import { DataService } from './data.service';

@NgModule({
  declarations: [
    AppComponent
  ],
  providers: [DataService],
  bootstrap: [AppComponent]
})
export class AppModule { }

2. Describe the purpose of data binding in Angular and its different types (one-way, two-way).

Data binding is the automatic synchronization of data between the model and the view. There are two types:

One-Way Data Binding:

• Interpolation: Embedding expressions in double curly braces {{}} within templates.

<!-- app.component.html -->
<p>{{ title }}</p>

Two-Way Data Binding:

• [(ngModel)]: Enables bidirectional data binding for form controls.

<!-- app.component.html -->
<input [(ngModel)]="userInput" />

3. Explain the concept of dependency injection in Angular and its benefits.

Dependency injection is a design pattern where a class receives its dependencies from external sources rather than creating them itself. Angular’s DI system provides dependencies to a class when it’s requested.

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  constructor(private dataService: DataService) {
    console.log(dataService.getData());
  }
}

4. Differentiate between routing and navigation in Angular and provide examples.

Routing:

Routing is the process of navigating between different components in an Angular application. It involves defining routes and associating them with components.

// app-routing.module.ts
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { HomeComponent } from './home.component';
import { AboutComponent } from './about.component';

const routes: Routes = [
  { path: 'home', component: HomeComponent },
  { path: 'about', component: AboutComponent },
];

@NgModule({
  imports: [RouterModule.forRoot(routes)],
  exports: [RouterModule]
})
export class AppRoutingModule { }

Navigation:

Navigation is the act of moving between different views in an Angular application. It involves using the routerLink directive or programmatically navigating in the component code.

<!-- app.component.html -->
<a routerLink="/home">Home</a>
<a routerLink="/about">About</a>

5. Describe the various lifecycle hooks available in Angular components and their functionalities

Angular components have a lifecycle that goes through various phases. Some notable hooks are:

• ngOnInit: Called once the component is initialized.
• ngOnChanges: Called

when the component’s input properties change.

import { Component, Input, OnChanges, SimpleChanges } from '@angular/core';

@Component({
  selector: 'app-child',
  template: '<p>{{ message }}</p>'
})
export class ChildComponent implements OnChanges {
  @Input() message: string;

  ngOnChanges(changes: SimpleChanges): void {
    console.log('Input properties changed:', changes);
  }
}

• ngOnDestroy: Called just before the component is destroyed. Useful for cleanup.

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

@Component({
  selector: 'app-cleanup',
  template: '<p>Cleanup Component</p>'
})
export class CleanupComponent implements OnDestroy {
  ngOnDestroy(): void {
    console.log('Cleanup Component destroyed');
  }
}

These lifecycle hooks provide developers with control over the behavior of components at different stages, allowing them to execute code at the right moment in the component’s lifecycle.

Advanced Topics

1. Explain the difference between Ahead-of-Time (AOT) and Just-in-Time (JIT) compilation in Angular and their advantages/disadvantages.

Ahead-of-Time (AOT) Compilation:

• Compilation Time:
  • AOT: Occurs during the build process, before deploying the application.
• Advantages:
  • Faster Rendering: AOT compiles templates before runtime, resulting in faster rendering.
  • Smaller Bundle Size: Templates and styles are precompiled, reducing the bundle size.
  • Detect Template Errors: Template errors are caught during the build, not at runtime.
• Disadvantages:
  • Longer Build Times: AOT compilation adds time to the build process.
  • Limited Dynamic Features: Some dynamic features may be limited due to precompilation.

ng build --aot

Just-in-Time (JIT) Compilation:

• Compilation Time:
  • JIT: Occurs at runtime in the user’s browser.
• Advantages:
  • Faster Development: No need to wait for AOT compilation during development.
  • More Dynamic Features: Supports more dynamic template features.
• Disadvantages:
  • Slower Initial Load: Larger bundle size and slower initial rendering.
  • Runtime Template Errors: Template errors may only appear at runtime.

2. Describe how you would implement user authentication and authorization in an Angular application.

• Authentication:
  • Use Angular Router Guards to protect routes based on user authentication status.
  • Implement a service for user authentication with methods like login, logout, and token storage.
• Authorization:
  • Assign roles or permissions to users.
  • Use Angular Router Guards or custom directives to control access based on roles or permissions.

// auth.service.ts
@Injectable({
  providedIn: 'root'
})
export class AuthService {
  isLoggedIn = false;

  login(): void {
    // Perform authentication logic
    this.isLoggedIn = true;
  }

  logout(): void {
    // Perform logout logic
    this.isLoggedIn = false;
  }
}

3. Explain the differences between NgRx and traditional Angular services for state management.

NgRx:

• Centralized State:
  • Manages state in a central store.
• Actions and Reducers:
  • Uses actions and reducers to update the state in a predictable way.
• Advantages:
  • Predictable State Changes: Enforces a unidirectional data flow for predictable state changes.
  • Scalability: Suitable for large, complex applications.

Traditional Angular Services:

• Local Component State:
  • Manages state within individual components or services.
• Event Emitters/Subjects:
  • Uses events or observable subjects to communicate state changes.
• Advantages:
  • Simplicity: Easier to set up and understand for smaller applications.
  • Less Boilerplate: Requires less boilerplate code compared to NgRx.

// actions.ts
export const increment = createAction('[Counter] Increment');

// reducer.ts
export const counterReducer = createReducer(
  initialState,
  on(increment, (state) => ({ ...state, count: state.count + 1 }))
);

4. Discuss strategies for optimizing the performance of an Angular application.

• Lazy Loading:
  • Use Angular’s lazy loading to load modules on demand.
• Minification and Compression:
  • Minify and compress JavaScript, CSS, and HTML files.
• Tree Shaking:
  • Remove unused code during the build process.
• Ahead-of-Time (AOT) Compilation:
  • Compile templates ahead of time for faster rendering.
• Optimized Images:
  • Compress and serve images in appropriate formats.

5. Explain how you would approach testing different aspects of an Angular application (unit, integration, end-to-end).

Unit Testing:

• Tools:
  • Jasmine for writing test cases.
  • Karma as a test runner.

// sample.component.spec.ts
describe('SampleComponent', () => {
  it('should create', () => {
    const component = new SampleComponent();
    expect(component).toBeTruthy();
  });
});

Integration Testing:

• Tools:
  • Use TestBed for testing Angular components with their templates.

// sample.component.spec.ts
describe('SampleComponent', () => {
  beforeEach(async(() => {
    TestBed.configureTestingModule({
      declarations: [SampleComponent],
    }).compileComponents();
  }));

  it('should create', () => {
    const fixture = TestBed.createComponent(SampleComponent);
    const component = fixture.componentInstance;
    expect(component).toBeTruthy();
  });
});

End-to-End Testing:

• Tools:
  • Protractor for end-to-end testing.

// app.e2e-spec.ts
describe('App', () => {
  it('should display welcome message', () => {
    browser.get('/');
    expect(element(by.css('app-root h1')).getText()).toEqual('Welcome to my-app!');
  });
});

Hands-on Scenarios

Write a simple Angular component that displays a list of items from an API using HttpClient.

// item-list.component.ts
import { Component, OnInit } from '@angular/core';
import { HttpClient } from '@angular/common/http';

@Component({
  selector: 'app-item-list',
  template: `
    <h2>Item List</h2>
    <ul>
      <li *ngFor="let item of items">{{ item.name }}</li>
    </ul>
  `
})
export class ItemListComponent implements OnInit {
  items: any[];

  constructor(private http: HttpClient) {}

  ngOnInit(): void {
    this.http.get<any[]>('https://api.example.com/items')
      .subscribe(data => this.items = data);
  }
}

2. Implement a custom directive in Angular that adds specific functionality to an element.

// highlight.directive.ts
import { Directive, ElementRef, Renderer2, Input } from '@angular/core';

@Directive({
  selector: '[appHighlight]'
})
export class HighlightDirective {
  @Input() highlightColor: string = 'yellow';

  constructor(private el: ElementRef, private renderer: Renderer2) {}

  ngOnInit() {
    this.renderer.setStyle(this.el.nativeElement, 'background-color', this.highlightColor);
  }
}

// app.component.ts
import { Component } from '@angular/core';

@Component({
  selector: 'app-root',
  template: `<p appHighlight [highlightColor]="'cyan'">This is highlighted!</p>`
})
export class AppComponent {}

3. Create a reactive form in Angular with validation rules.

// user-form.component.ts
import { Component } from '@angular/core';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';

@Component({
  selector: 'app-user-form',
  template: `
    <form [formGroup]="userForm" (ngSubmit)="onSubmit()">
      <label for="name">Name:</label>
      <input type="text" id="name" formControlName="name" />

      <label for="email">Email:</label>
      <input type="email" id="email" formControlName="email" />

      <button type="submit" [disabled]="userForm.invalid">Submit</button>
    </form>
  `
})
export class UserFormComponent {
  userForm: FormGroup;

  constructor(private fb: FormBuilder) {
    this.userForm = this.fb.group({
      name: ['', Validators.required],
      email: ['', [Validators.required, Validators.email]]
    });
  }

  onSubmit() {
    // Handle form submission
    console.log(this.userForm.value);
  }
}

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Angular Interview Questions for Mid-Level Developers – 2024