Angular Interview Questions: From Beginners to Advance (Part 1)

Welcome to the first part of our series on Angular interview questions! In this section, we’ll cover a range of topics from beginner to advanced levels, providing you with insights and examples to help you prepare for your next Angular interview.

1. What is the significance of View and Encapsulation in Angular?

In Angular, the View represents the user interface (UI) of an application. It consists of HTML templates that are rendered to display data and interact with users. Encapsulation is the process of encapsulating the styles and behavior of a component to prevent them from affecting other parts of the application.

Example:

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
  encapsulation: ViewEncapsulation.None // Disable encapsulation
})
export class AppComponent {
  // Component logic goes here
}

2. How do Pipes work in Angular?

In Angular, Pipes are used to transform data before displaying it in the UI. Angular provides built-in pipes for common transformations like date formatting, currency conversion, and uppercase/lowercase conversions.

Example:

<!-- app.component.html -->
<p>{{ today | date:'shortDate' }}</p>

3. What is the purpose of a Pure Pipe in Angular?

A Pure Pipe in Angular is a pipe that is stateless and only re-evaluates when its input value changes. This improves performance by preventing unnecessary recalculations.

Example:

// custom-pipe.pipe.ts
import { Pipe, PipeTransform } from '@angular/core';

@Pipe({
  name: 'customPipe',
  pure: true
})
export class CustomPipe implements PipeTransform {
  transform(value: any): any {
    // Transformation logic
    return transformedValue;
  }
}

4. What are the different ways to call a REST API in Angular?

Angular provides several methods for calling REST APIs, including the HttpClient module, the Http module (deprecated in newer Angular versions), and third-party libraries like Axios.

Example using HttpClient:

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

@Injectable({
  providedIn: 'root'
})
export class DataService {
  constructor(private http: HttpClient) {}

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

5. How does Lazy Loading work in Angular?

Lazy Loading in Angular allows you to load modules asynchronously when they are needed, improving the initial loading time of the application.

Example:

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

const routes: Routes = [
  { path: 'lazy', loadChildren: () => import('./lazy/lazy.module').then(m => m.LazyModule) }
];

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

6. What is Change Detection in Angular?

Change Detection is a core mechanism in Angular that ensures the application’s UI reflects the current state of data. Angular automatically detects changes to data in the component and its child components, and updates the view accordingly.

Example:

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  counter: number = 0;

  incrementCounter() {
    this.counter++;
  }
}

<!-- app.component.html -->
<p>Counter: {{ counter }}</p>
<button (click)="incrementCounter()">Increment</button>

7. Can you explain the concept of Angular Directives?

Angular Directives are markers on a DOM element that tell Angular to do something with that element or its children. They are a way to extend HTML to create reusable components or add behavior to existing elements.

Example:

<!-- app.component.html -->
<div appHighlight>Highlighted Text</div>

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

@Directive({
  selector: '[appHighlight]'
})
export class HighlightDirective {
  constructor(private el: ElementRef) {
    el.nativeElement.style.backgroundColor = 'yellow';
  }
}

8. How do ngIf and constructors work in Angular?

ngIf is a structural directive in Angular that conditionally includes or excludes a portion of the DOM based on the expression provided to it. Constructors in Angular are special methods used for initializing class instances.

Example:

<!-- app.component.html -->
<div *ngIf="isLoggedIn">
  <p>Welcome, User!</p>
</div>

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  isLoggedIn: boolean = false;

  constructor() {
    // Initialization logic
    this.isLoggedIn = true; // Simulating user login
  }
}

9. What is the purpose of the ng-pristine directive in Angular?

The ng-pristine directive in Angular is used to check if a form field has been interacted with or modified by the user. It indicates whether the field is in its initial state (pristine) or has been touched/modified (dirty).

Example:

<!-- app.component.html -->
<input type="text" ngModel name="username" #username="ngModel" required>
<div *ngIf="username.pristine">
  Please enter a username.
</div>

10. What is the role of the ng-content directive in Angular?

The ng-content directive in Angular is used for Content Projection. It allows you to pass content into a component from its parent component, enabling the creation of flexible and reusable components.

Example:

<!-- parent.component.html -->
<app-child>
  <h1>Child Component Content</h1>
</app-child>

<!-- child.component.html -->
<div>
  <ng-content></ng-content>
</div>

11. What is the significance of the OnPush change detection strategy in Angular?

The OnPush change detection strategy in Angular is a performance optimization technique that tells Angular to only run change detection on a component when its inputs change. It's particularly useful when dealing with immutable data or pure components to reduce unnecessary checks and improve application performance.

Example:

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css'],
  changeDetection: ChangeDetectionStrategy.OnPush // Set OnPush strategy
})
export class AppComponent {
  // Component logic goes here
}

12. Which testing framework have you used in Angular development?

In Angular development, popular testing frameworks include Jasmine and Karma. Jasmine is a behavior-driven development framework for testing JavaScript code, and Karma is a test runner that launches browsers and executes tests.

Example (Jasmine):

// example.spec.ts
import { Calculator } from './calculator';

describe('Calculator', () => {
  let calculator: Calculator;

  beforeEach(() => {
    calculator = new Calculator();
  });

  it('should add two numbers', () => {
    expect(calculator.add(1, 2)).toEqual(3);
  });
});

13. What is a Standalone component?

A Standalone component in Angular is a component that doesn’t depend on other Angular modules or services. It can be easily reused and tested independently, making it a valuable building block for Angular applications.

Example:

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

@Component({
  selector: 'app-standalone',
  template: '<p>This is a standalone component</p>'
})
export class StandaloneComponent {
  // Component logic goes here
}

14. How do template-driven forms work in Angular?

Template-driven forms in Angular use directives like ngModel to create a two-way data binding between form controls in the template and properties in the component class. They are easier to set up and understand but may not be suitable for complex forms.

Example:

<!-- app.component.html -->
<form #form="ngForm" (ngSubmit)="onSubmit(form.value)">
  <input type="text" name="username" ngModel required>
  <button type="submit">Submit</button>
</form>

15. How do reactive forms work in Angular?

Reactive forms in Angular use a model-driven approach, where form controls are created programmatically in the component class. They offer more flexibility and control over form validation and submission, making them suitable for complex forms.

Example:

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

@Component({
  selector: 'app-root',
  templateUrl: './app.component.html',
  styleUrls: ['./app.component.css']
})
export class AppComponent {
  form: FormGroup;

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

  onSubmit() {
    if (this.form.valid) {
      // Form submission logic
    }
  }
}

<!-- app.component.html -->
<form [formGroup]="form" (ngSubmit)="onSubmit()">
  <input type="text" formControlName="username">
  <button type="submit">Submit</button>
</form>

Conclusion:

In this first part of our Angular interview questions series, we’ve covered a range of topics from fundamental concepts to more advanced techniques. By understanding these concepts and examples, you’ll be better prepared to tackle Angular-related questions in your next interview.

Stay tuned for more Angular interview questions and answers in our upcoming parts!

Next Parts:

• Angular Interview Questions: From Beginners to Advance (Part 2)
• Angular Interview Questions: From Beginners to Advance (Part 3)

Happy coding!