Top 30 Angular Interview Questions for Experienced Developers

Angular is one of the most popular front-end frameworks for building dynamic, single-page applications (SPAs). Whether you're preparing for a technical interview or just looking to deepen your understanding of Angular, this article covers the top 30 Angular interview questions with detailed explanations and examples. Let's dive in!

1. What is Angular, and what are its key features?

Angular is a TypeScript-based open-source front-end web application framework developed by Google. It is used to build dynamic, single-page applications (SPAs) with a modular architecture.

Key Features:

• Two-Way Data Binding: Automatically synchronizes data between the model and the view.
• Dependency Injection: Simplifies the management of dependencies and promotes modularity.
• Component-Based Architecture: Build applications using reusable components.
• TypeScript Support: Provides strong typing and advanced tooling for better development.

Key Takeaways:

• Angular is a powerful framework for building SPAs.
• Its features like two-way data binding and dependency injection make development efficient and scalable.

2. What is the difference between AngularJS and Angular?

AngularJS: The first version of Angular, based on JavaScript. It uses controllers and scope for managing data.

Angular: A complete rewrite of AngularJS, based on TypeScript. It uses components and modules for building applications.

Key Differences:

• Language: AngularJS uses JavaScript, while Angular uses TypeScript.
• Architecture: AngularJS uses MVC, while Angular uses component-based architecture.
• Performance: Angular is faster and more efficient than AngularJS.

Key Takeaways:

• Angular is a modern, TypeScript-based framework, while AngularJS is legacy.
• Angular offers better performance and scalability.

3. What are Angular components?

Components are the building blocks of an Angular application. They consist of a TypeScript class (for logic), an HTML template (for the view), and CSS styles (for styling).

  // Example: Angular Component
  import { Component } from '@angular/core';

  @Component({
      selector: 'app-root',
      template: `<h1>Hello, {{name}}!</h1>`,
      styles: [`h1 { color: blue; }`]
  })
  export class AppComponent {
      name = 'Angular';
  }
  

Key Takeaways:

• Components encapsulate the logic, view, and styles of a part of the UI.
• They are reusable and promote modularity.

4. What is Angular's data binding, and what are its types?

Data binding is a mechanism that synchronizes data between the component and the view. Angular supports four types of data binding:

• Interpolation: Displays component data in the view using `{{ }}`.
• Property Binding: Binds component data to an HTML element property using `[]`.
• Event Binding: Listens for user events and triggers component methods using `()`.
• Two-Way Binding: Combines property and event binding to synchronize data between the component and the view using `[()]`.

  
  <h1>{{title}}</h1>  
  <img [src]="imageUrl">  
  <button (click)="onClick()">Click Me</button>  
  <input [(ngModel)]="name">  
  

Key Takeaways:

• Data binding simplifies the synchronization of data between the component and the view.
• Two-way binding is a powerful feature for real-time updates.

5. What is Angular's dependency injection, and how does it work?

Dependency Injection (DI) is a design pattern used in Angular to provide dependencies (e.g., services) to components or other services. It promotes modularity and testability.

  // Example: Dependency Injection
  import { Injectable } from '@angular/core';

  @Injectable({
      providedIn: 'root'
  })
  export class DataService {
      getData() {
          return 'Hello, Angular!';
      }
  }

  // Injecting the service into a component
  export class AppComponent {
      constructor(private dataService: DataService) {}

      ngOnInit() {
          console.log(this.dataService.getData());
      }
  }
  

Key Takeaways:

• Dependency Injection simplifies the management of dependencies.
• It makes code more modular, reusable, and testable.

6. What are Angular directives, and what are their types?

Directives are instructions in the DOM that tell Angular how to transform or manipulate elements. There are three types of directives:

• Component Directives: Define custom elements with templates and logic.
• Structural Directives: Modify the DOM layout by adding or removing elements (e.g., `*ngIf`, `*ngFor`).
• Attribute Directives: Change the appearance or behavior of elements (e.g., `ngStyle`, `ngClass`).

  
  <div *ngIf="isVisible">Visible Content</div>  
  <div [ngClass]="{'active': isActive}">Styled Content</div>  
  

Key Takeaways:

• Directives are powerful tools for manipulating the DOM.
• They enhance the functionality and flexibility of Angular applications.

7. What is Angular's change detection, and how does it work?

Change detection is the process by which Angular updates the view when the component's data changes. Angular uses a unidirectional data flow and checks for changes in the component tree.

Key Features:

• Zone.js: Monitors asynchronous operations and triggers change detection.
• OnPush Strategy: Optimizes performance by checking only when input properties change.

  // Example: OnPush Change Detection Strategy
  import { ChangeDetectionStrategy, Component } from '@angular/core';

  @Component({
      selector: 'app-root',
      template: `<h1>{{title}}</h1>`,
      changeDetection: ChangeDetectionStrategy.OnPush
  })
  export class AppComponent {
      title = 'Angular';
  }
  

Key Takeaways:

• Change detection ensures the view stays in sync with the component's data.
• The OnPush strategy improves performance by reducing unnecessary checks.

8. What is Angular's routing, and how does it work?

Angular's routing allows you to navigate between different views or components in a single-page application. It uses the `RouterModule` to define routes and manage navigation.

  // Example: Angular Routing
  import { RouterModule, Routes } from '@angular/router';
  import { HomeComponent } from './home/home.component';
  import { AboutComponent } from './about/about.component';

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

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

Key Takeaways:

• Routing enables navigation between views in a single-page application.
• It is essential for building multi-view applications.

9. What is Angular's HttpClient, and how is it used?

The `HttpClient` module is used to make HTTP requests in Angular. It provides methods for GET, POST, PUT, DELETE, and other HTTP operations.

  // Example: Using HttpClient
  import { HttpClient } from '@angular/common/http';
  import { Injectable } from '@angular/core';

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

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

Key Takeaways:

• `HttpClient` simplifies making HTTP requests in Angular.
• It supports features like interceptors and error handling.

10. What is Angular's reactive forms, and how are they used?

Reactive forms are a model-driven approach to handling form inputs in Angular. They provide more control and flexibility compared to template-driven forms.

  // Example: Reactive Forms
  import { FormBuilder, FormGroup, Validators } from '@angular/forms';

  @Component({
      selector: 'app-root',
      template: `
          <form [formGroup]="form" (ngSubmit)="onSubmit()">
              <input formControlName="name">
              <button type="submit">Submit</button>
          </form>
      `
  })
  export class AppComponent {
      form: FormGroup;

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

      onSubmit() {
          console.log(this.form.value);
      }
  }
  

Key Takeaways:

• Reactive forms provide more control and flexibility for handling form inputs.
• They are ideal for complex forms with dynamic behavior.

11. What is Angular's template-driven forms, and how are they used?

Template-driven forms are a simpler approach to handling form inputs in Angular. They rely on directives like `ngModel` and are ideal for basic forms.

  // Example: Template-Driven Forms
  import { Component } from '@angular/core';

  @Component({
      selector: 'app-root',
      template: `
          <form #form="ngForm" (ngSubmit)="onSubmit(form)">
              <input name="name" ngModel>
              <button type="submit">Submit</button>
          </form>
      `
  })
  export class AppComponent {
      onSubmit(form: NgForm) {
          console.log(form.value);
      }
  }
  

Key Takeaways:

• Template-driven forms are simpler and easier to implement for basic forms.
• They rely on directives like `ngModel` for two-way data binding.

12. What is Angular's ViewChild and ViewChildren, and how are they used?

`ViewChild`: A decorator used to access a single child element or component in the view.

`ViewChildren`: A decorator used to access multiple child elements or components in the view.

  // Example: ViewChild and ViewChildren
  import { Component, ViewChild, ViewChildren, ElementRef, QueryList } from '@angular/core';

  @Component({
      selector: 'app-root',
      template: `
          <div #child>Child Element</div>
          <div #child>Another Child Element</div>
      `
  })
  export class AppComponent {
      @ViewChild('child') child: ElementRef;
      @ViewChildren('child') children: QueryList<ElementRef>;

      ngAfterViewInit() {
          console.log(this.child.nativeElement.textContent);
          this.children.forEach(child => console.log(child.nativeElement.textContent));
      }
  }
  

Key Takeaways:

• `ViewChild` and `ViewChildren` are used to access child elements or components.
• They are essential for interacting with the DOM in Angular.

13. What is Angular's ContentChild and ContentChildren, and how are they used?

`ContentChild`: A decorator used to access a single content-projected element or component.

`ContentChildren`: A decorator used to access multiple content-projected elements or components.

  // Example: ContentChild and ContentChildren
  import { Component, ContentChild, ContentChildren, ElementRef, QueryList } from '@angular/core';

  @Component({
      selector: 'app-parent',
      template: `
          <ng-content></ng-content>
      `
  })
  export class ParentComponent {
      @ContentChild('child') child: ElementRef;
      @ContentChildren('child') children: QueryList<ElementRef>;

      ngAfterContentInit() {
          console.log(this.child.nativeElement.textContent);
          this.children.forEach(child => console.log(child.nativeElement.textContent));
      }
  }
  

Key Takeaways:

• `ContentChild` and `ContentChildren` are used to access content-projected elements.
• They are essential for working with transclusion in Angular.

14. What is Angular's ng-template, and how is it used?

`ng-template` is a directive used to define template fragments that can be conditionally rendered or reused. It is often used with structural directives like `ngIf` and `ngFor`.

  
  <ng-template #templateRef>
      <p>This is a template.</p>
  </ng-template>

  <div *ngIf="isVisible; else templateRef">
      Visible Content
  </div>
  

Key Takeaways:

• `ng-template` is used to define reusable or conditional template fragments.
• It is essential for creating dynamic and reusable UI components.

15. What is Angular's ng-container, and how is it used?

`ng-container` is a logical container that does not render any additional DOM elements. It is used to group elements without introducing extra nodes in the DOM.

  
  <ng-container *ngIf="isVisible">
      <p>This content is conditionally rendered.</p>
  </ng-container>
  

Key Takeaways:

• `ng-container` is used to group elements without adding extra DOM nodes.
• It is ideal for conditional rendering and structural directives.

16. What is Angular's ng-content, and how is it used?

`ng-content` is a directive used for content projection, allowing you to insert external content into a component's template. It is commonly used to create reusable components.

  
  
  <app-card>
      <p>This content is projected into the card.</p>
  </app-card>

  
  <div class="card">
      <ng-content></ng-content>
  </div>
  

Key Takeaways:

• `ng-content` is used for content projection, making components more flexible and reusable.
• It allows you to pass HTML content from a parent component to a child component.

17. What is Angular's ng-template outlet, and how is it used?

`ng-template outlet` is used to render a template dynamically using `ng-template`. It is often used with `ngTemplateOutlet` to create reusable and dynamic templates.

  
  <ng-template #templateRef>
      <p>This is a dynamic template.</p>
  </ng-template>

  <ng-container *ngTemplateOutlet="templateRef"></ng-container>
  

Key Takeaways:

• `ng-template outlet` is used to render templates dynamically.
• It is ideal for creating reusable and dynamic UI components.

18. What is Angular's ngClass, and how is it used?

`ngClass` is a directive used to dynamically add or remove CSS classes based on component data. It supports multiple class bindings and conditional logic.

  
  <div [ngClass]="{'active': isActive, 'disabled': isDisabled}">
      Dynamic Class Binding
  </div>
  

Key Takeaways:

• `ngClass` is used for dynamic class binding based on component data.
• It supports multiple classes and conditional logic.

19. What is Angular's ngStyle, and how is it used?

`ngStyle` is a directive used to dynamically apply inline styles based on component data. It supports multiple style bindings and conditional logic.

  
  <div [ngStyle]="{'color': textColor, 'font-size': fontSize + 'px'}">
      Dynamic Style Binding
  </div>
  

Key Takeaways:

• `ngStyle` is used for dynamic inline style binding based on component data.
• It supports multiple styles and conditional logic.

20. What is Angular's ngSwitch, and how is it used?

`ngSwitch` is a structural directive used to conditionally render content based on a switch expression. It is similar to a switch statement in JavaScript.

  
  <div [ngSwitch]="status">
      <p *ngSwitchCase="'active'">Active</p>
      <p *ngSwitchCase="'inactive'">Inactive</p>
      <p *ngSwitchDefault>Unknown</p>
  </div>
  

Key Takeaways:

• `ngSwitch` is used for conditional rendering based on a switch expression.
• It is ideal for scenarios with multiple conditions.

21. What is Angular's ngFor, and how is it used?

`ngFor` is a structural directive used to iterate over a collection (e.g., an array) and render a template for each item. It is commonly used to display lists or tables.

  
  <ul>
      <li *ngFor="let item of items; let i = index">
          {{i + 1}}. {{item.name}}
      </li>
  </ul>
  

Key Takeaways:

• `ngFor` is used to iterate over collections and render dynamic content.
• It supports additional features like `index`, `first`, `last`, and `trackBy`.

22. What is Angular's trackBy, and how is it used?

`trackBy` is a function used with `ngFor` to improve performance by tracking items in a collection. It helps Angular identify which items have changed, been added, or been removed.

  // Example: trackBy Function
  export class AppComponent {
      items = [
          { id: 1, name: 'Item 1' },
          { id: 2, name: 'Item 2' }
      ];

      trackByFn(index: number, item: any): number {
          return item.id;  // Track items by their unique ID
      }
  }
  

  
  <ul>
      <li *ngFor="let item of items; trackBy: trackByFn">
          {{item.name}}
      </li>
  </ul>
  

Key Takeaways:

• `trackBy` improves performance by minimizing DOM updates.
• It is essential for optimizing large lists or frequently updated collections.

23. What is Angular's ngIf, and how is it used?

`ngIf` is a structural directive used to conditionally render content based on a boolean expression. It adds or removes elements from the DOM based on the condition.

  
  <div *ngIf="isVisible">
      Visible Content
  </div>
  

Key Takeaways:

• `ngIf` is used for conditional rendering of elements.
• It is ideal for showing or hiding content based on component data.

24. What is Angular's ngIf-else, and how is it used?

`ngIf-else` is an extension of `ngIf` that allows you to specify an alternative template when the condition is false. It uses `ng-template` to define the else block.

  
  <div *ngIf="isVisible; else elseBlock">
      Visible Content
  </div>
  <ng-template #elseBlock>
      <p>Hidden Content</p>
  </ng-template>
  

Key Takeaways:

• `ngIf-else` is used for conditional rendering with an alternative template.
• It is ideal for scenarios where you need to display fallback content.

25. What is Angular's ngPlural, and how is it used?

`ngPlural` is a directive used to conditionally render content based on a numeric value. It is commonly used for pluralization (e.g., "1 item" vs. "2 items").

  
  <div [ngPlural]="itemCount">
      <ng-template ngPluralCase="=0">No items</ng-template>
      <ng-template ngPluralCase="=1">1 item</ng-template>
      <ng-template ngPluralCase="other">{{itemCount}} items</ng-template>
  </div>
  

Key Takeaways:

• `ngPlural` is used for conditional rendering based on numeric values.
• It is ideal for pluralization and handling multiple numeric conditions.

26. What is Angular's ngNonBindable, and how is it used?

`ngNonBindable` is a directive used to prevent Angular from compiling or binding content within an element. It is useful for displaying Angular syntax without interpreting it.

  
  <div ngNonBindable>
      This content will not be compiled: {{name}}
  </div>
  

Key Takeaways:

• `ngNonBindable` is used to display Angular syntax without binding or compilation.
• It is ideal for documentation or displaying code snippets.

27. What is Angular's ngModel, and how is it used?

`ngModel` is a directive used for two-way data binding in Angular. It synchronizes data between the component and the view, making it easy to manage form inputs.

  
  <input [(ngModel)]="name" placeholder="Enter your name">
  <p>Hello, {{name}}!</p>
  

Key Takeaways:

• `ngModel` is used for two-way data binding in forms.
• It simplifies the synchronization of data between the component and the view.

28. What is Angular's ngModelChange, and how is it used?

`ngModelChange` is an event emitted by `ngModel` when the value of a form control changes. It allows you to perform custom logic when the value updates.

  
  <input [ngModel]="name" (ngModelChange)="onNameChange($event)" placeholder="Enter your name">
  

  // Example: Handling ngModelChange
  export class AppComponent {
      name = '';

      onNameChange(newName: string) {
          console.log('Name changed to:', newName);
          this.name = newName;
      }
  }
  

Key Takeaways:

• `ngModelChange` is used to handle value changes in form controls.
• It allows you to perform custom logic when the value updates.

29. What is Angular's ngForm, and how is it used?

`ngForm` is a directive used to create template-driven forms in Angular. It provides a way to track form state, validate inputs, and handle submissions.

  
  <form #form="ngForm" (ngSubmit)="onSubmit(form)">
      <input name="name" ngModel required>
      <button type="submit">Submit</button>
  </form>
  

  // Example: Handling Form Submission
  export class AppComponent {
      onSubmit(form: NgForm) {
          console.log(form.value);  // Form data
          console.log(form.valid);  // Form validity
      }
  }
  

Key Takeaways:

• `ngForm` is used to create and manage template-driven forms.
• It provides features like form state tracking, validation, and submission handling.

30. What is Angular's ngModelGroup, and how is it used?

`ngModelGroup` is a directive used to group form controls in template-driven forms. It allows you to organize and validate related controls together.

  
  <form #form="ngForm" (ngSubmit)="onSubmit(form)">
      <div ngModelGroup="user">
          <input name="firstName" ngModel required>
          <input name="lastName" ngModel required>
      </div>
      <button type="submit">Submit</button>
  </form>
  

  // Example: Handling Grouped Form Data
  export class AppComponent {
      onSubmit(form: NgForm) {
          console.log(form.value.user);  // Grouped form data
      }
  }
  

Key Takeaways:

• `ngModelGroup` is used to group and organize related form controls.
• It simplifies form management and validation for complex forms.

Congratulations! You've now explored the top 30 Angular interview questions. These concepts are essential for mastering Angular and excelling in technical interviews. Keep practicing, and happy coding!