Angular Interview Questions

Angular Interview Questions

What is Angular Framework?

Angular is a TypeScript-based open-source front-end platform that makes it easy to build web, mobile and desktop applications. The major features of this framework include declarative templates, dependency injection, end to end tooling which ease application development.

What are the key features of Angular?

Angular is a popular open-source web application framework developed by Google. Its key features are:

  • Two-way data binding: Syncs model and view changes.
  • MVVM architecture: Organizes code efficiently via Model-View-ViewModel pattern.
  • Dependency Injection (DI): Manages component dependencies for modularity.
  • Directives: Extend HTML for custom components and behavior.
  • Component-based architecture: Uses reusable, self-contained code pieces.
  • Services: Singletons for app-wide functionality like data sharing.
  • Routing: Creates SPAs with seamless navigation.
  • Forms: Supports template-driven and reactive forms with validation.
  • HTTP client: Simplifies server communication and error handling.
  • Testing support: Provides tools for unit, end-to-end, and integration testing.
  • CLI (Command Line Interface): Facilitates app setup, testing, and deployment.

What is the difference between AngularJS and Angular?

Some key difference between AngularJS and Angular:

Feature AngularJS Angular
Architecture Follows MVC (Model-View-Controller) architecture. Follows MVVM (Model-View-ViewModel) architecture.
Language Written in JavaScript. Written in TypeScript, a superset of JavaScript.
Performance Generally slower due to digest cycle and scope. Generally faster with optimized rendering and change detection.
Dependency Injection Uses AngularJS's own DI system. Utilizes a more advanced and standardized DI system.
Mobile Development Lacks native support for mobile development. Supports mobile development through frameworks like Ionic.
Tooling Limited tooling compared to Angular. Has a comprehensive CLI (Command Line Interface) for scaffolding, testing, and deployment.

Explain Angular Modules.

Angular Modules, also known as NgModules, are containers for different parts of an Angular application. They help in organizing the application into cohesive blocks of functionality. Every Angular app has at least one module, the root module.

What is Data Binding in Angular?

Data binding is the automatic synchronization of data between the model and the view components. Angular supports both one-way and two-way data binding, enabling seamless interaction between the application logic and the UI.

Explain Dependency Injection in Angular.

Dependency Injection (DI) is a design pattern used in Angular to create and manage dependencies between different components or services. It helps in making components more modular, reusable, and easier to test.

What is Angular Routing?

Angular Routing is a mechanism for navigating between different views or pages in a single-page application. It allows developers to define routes and associate them with specific components, enabling the creation of a rich and dynamic user experience.

With Angular routing, we can:

  • Define routes: You specify routes in the application module's routing configuration, associating each route with a component.
  • Navigate programmatically: You can navigate between routes programmatically using Angular's Router service.
  • Handle route parameters: Routes can have parameters in the URL, which can be accessed and utilized by the corresponding component.
  • Lazy loading: Angular supports lazy loading, allowing you to load modules and their associated routes only when needed, improving performance by reducing initial bundle size.
  • Guard routes: Angular provides guards to control access to routes based on certain conditions, such as authentication or user roles.

What are Angular Directives?

Angular Directives are markers on a DOM element that tell Angular to do something to that element or its children. They can be classified into three types: component directives, structural directives, and attribute directives.

What is ViewChild in Angular?

ViewChild is a decorator in Angular used to query and access child components, directives, or DOM elements from within a parent component. It allows parent components to interact with their children and access their properties or methods.

Explain Angular Forms and Form Validation.

Angular Forms and Form Validation are features provided by the Angular framework to facilitate the creation and validation of HTML forms within web applications.

Angular Forms: Angular supports two types of forms: template-driven forms and reactive forms.

  • Template-driven forms: In template-driven forms, form controls are defined directly within the HTML template using directives such as ngModel to bind input elements to properties in the component class. Template-driven forms are suitable for simpler forms with less complex validation requirements.
  • Reactive forms: Reactive forms are model-driven forms where form controls are created programmatically in the component class using Angular's FormControl, FormGroup, and FormArray classes. Reactive forms offer more flexibility and control, making them suitable for complex forms with dynamic validation requirements.

Form Validation: Angular provides built-in mechanisms for form validation to ensure that user input meets certain criteria before it is submitted. Form validation can be performed both on the client-side (in the browser) and on the server-side.

  • Built-in validators: Angular provides a set of built-in validators such as required, minLength, maxLength, pattern, etc., which can be applied to form controls using directives or programmatically.
  • Custom validators: Angular allows you to define custom validators to implement custom validation logic for form controls based on specific requirements.
  • Validation feedback: Angular provides mechanisms for displaying validation feedback to users, such as displaying error messages next to form controls or applying CSS classes to highlight invalid input.
  • Form status and validity: Angular forms have properties to track their overall status and validity, which can be used to enable/disable form submission buttons or perform other actions based on the form's validity.

What is Angular Interpolation?

Angular Interpolation is a way to bind expressions in Angular templates. It uses double curly braces to evaluate expressions and display their results in the HTML template.

What is Angular HttpClient?

HttpClient is a built-in Angular module that provides a simplified API for making HTTP requests to web servers. It supports features like request and response interception, error handling, and progress events.

What is Angular Service and why is it used?

An Angular Service is a TypeScript class that encapsulates reusable functionality and provides it to other parts of the application. Services are used to share data, perform common tasks, and maintain state across different components.

Explain Angular Pipes.

Angular Pipes are a feature that allows you to transform data in your templates before displaying it to the user. They are used to format data, apply filters, and perform other transformations such as currency conversion or date formatting.

What is Angular Testing and why is it important?

Angular Testing involves writing and executing tests to ensure that Angular applications behave as expected. It helps in identifying and fixing bugs, improving code quality, and maintaining application reliability over time.

What are Angular Guards and why are they used?

Angular Guards are interfaces that allow developers to implement logic to control navigation in an Angular application. They are used to protect routes, perform authentication, and enforce access control based on certain conditions.

What is the difference between AngularJS and Angular?

Here are some of the major difference between AngularJS and Angular:

AngularJs Angular
It is based on MVC architecture This is based on the Service/Controller
It uses JavaScript to build the application Uses TypeScript to build the application
Based on the controller concept This is a component-based UI approach
Difficult to build SEO-friendly application Fully supports mobile platforms
Difficult to build SEO-friendly application Ease to build SEO friendly applications

What are the key components of Angular?

Angular has the key components below,

  • Component: These are the basic building blocks of an Angular application to control HTML views.
  • Modules: An Angular module is a set of angular basic building blocks like components, directives, services etc. An application is divided into logical pieces and each piece of code is called as "module" which perform a single task.
  • Templates: These represent the views of an Angular application.
  • Services: Are used to create components which can be shared across the entire application.
  • Metadata: This can be used to add more data to an Angular class.

What are directives?

Directives add behaviour to an existing DOM element or an existing component instance.

import { Directive, ElementRef, Input } from '@angular/core';

@Directive({ selector: '[myHighlight]' })
export class HighlightDirective {
    constructor(el: ElementRef) { = 'yellow';

Now this directive extends HTML element behavior with a yellow background as below

<p myHighlight>Highlight me!</p>

What are components?

Components are the most basic UI building block of an Angular app, which form a tree of Angular components. These components are a subset of directives. Unlike directives, components always have a template, and only one component can be instantiated per element in a template. Let's see a simple example of Angular component.

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

@Component ({
   selector: 'my-app',
   template: ` <div>
      <div>Learn Angular6 with examples</div>
   </div> `,

export class AppComponent {
   title: string = 'Welcome to Angular world';

What is a template?

Modules are logical boundaries in your application, and the application is divided into separate modules to separate the functionality of your application. Let's take an example of app.module.ts root module declared with @NgModule decorator as below,

import { NgModule }      from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent }  from './app.component';

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

The NgModule decorator has five important (among all) options:

  • The imports option is used to import other dependent modules. The BrowserModule is required by default for any web-based angular application.
  • The declarations option is used to define components in the respective module.
  • The bootstrap option tells Angular which Component to bootstrap in the application.
  • The provider's option is used to configure a set of injectable objects that are available in the injector of this module.
  • The entryComponents option is a set of components dynamically loaded into the view.

What are lifecycle hooks available?

Angular application goes through an entire set of processes or has a lifecycle right from its initiation to the end of the application. The representation of lifecycle in pictorial representation as follows,

The description of each lifecycle method is as below,

  • ngOnChanges: When the value of a data-bound property changes, then this method is called.
  • ngOnInit: This is called whenever the initialization of the directive/component after Angular first displays the data-bound properties happens.
  • ngDoCheck: This is for the detection and to act on changes that Angular can't or won't detect on its own.
  • ngAfterContentInit: This is called in response after Angular projects external content into the component's view.
  • ngAfterContentChecked: This is called in response after Angular checks the content projected into the component.
  • ngAfterViewInit: This is called in response after Angular initializes the component's views and child views.
  • ngAfterViewChecked: This is called in response after Angular checks the component's views and child views.
  • ngOnDestroy: This is the cleanup phase just before Angular destroys the directive/component.

What is a data binding?

Data binding is a core concept in Angular and allows to define communication between a component and the DOM, making it very easy to define interactive applications without worrying about pushing and pulling data. There are four forms of data binding(divided as 3 categories) which differ in the way the data is flowing.

  • From the Component to the DOM:
    • Interpolation: : Adds the value of a property from the component
      <li>Name: </li>
      <li>Address: </li>
    • Property binding: [property]=”value”: The value is passed from the component to the specified property or simple HTML attribute
      <input type="email" [value]="">
  • From the DOM to the Component: Event binding: (event)=”function”: When a specific DOM event happens (eg.: click, change, keyup), call the specified method in the component
    <button (click)="logout()"></button>
  • Two-way binding: Two-way data binding: [(ngModel)]=”value”: Two-way data binding allows to have the data flow both ways. For example, in the below code snippet, both the email DOM input and component email property are in sync
    <input type="email" [(ngModel)]="">

What is metadata?

Metadata is used to decorate a class so that it can configure the expected behavior of the class. The metadata is represented by decorators.

What is angular CLI?

Angular CLI(Command Line Interface) is a command line interface to scaffold and build angular apps using nodejs style (commonJs) modules. You need to install using below npm command,

npm install @angular/cli@latest

Below are the list of few commands, which will come handy while creating angular projects

  • Creating New Project: ng new
  • Generating Components, Directives & Services: ng generate/g The different types of commands would be,
    • ng generate class my-new-class: add a class to your application
    • ng generate component my-new-component: add a component to your application
    • ng generate directive my-new-directive: add a directive to your application
    • ng generate enum my-new-enum: add an enum to your application
    • ng generate module my-new-module: add a module to your application
    • ng generate pipe my-new-pipe: add a pipe to your application
    • ng generate service my-new-service: add a service to your application
  • Running the Project: ng serve

Explain Angular Dependency Injection Tree.

Angular Dependency Injection Tree is a hierarchical structure that Angular uses to manage the dependencies between different parts of an application. It ensures that each component or service gets the correct instance of its dependencies when it is instantiated.

What is Angular Universal?

Angular Universal is a technology that allows developers to render Angular applications on the server side. It enables better performance, improved SEO, and support for progressive web apps (PWAs) by pre-rendering pages on the server before sending them to the client.

What are Angular Schematics?

Angular Schematics are templates or blueprints used by the Angular CLI to generate code for components, modules, services, and other Angular artifacts. They help in automating repetitive tasks and enforcing consistent project structures and coding standards.

Explain Angular Lazy Loading.

Angular Lazy Loading is a technique used to load parts of an application on-demand, instead of loading everything upfront. It improves application startup time and reduces initial bundle size by loading modules asynchronously when they are needed.

What is Angular Material?

Angular Material is a UI component library for Angular applications that provides a set of pre-built, customizable components following Google's Material Design guidelines. It includes components like buttons, cards, forms, and navigation elements.

What is NgRx and how does it work?

NgRx is a state management library for Angular applications based on the Redux pattern. It helps in managing application state in a predictable and immutable way by centralizing state in a single store and using actions and reducers to modify it.

How does Angular handle Dependency Injection across multiple modules?

Angular uses hierarchical injectors to manage dependencies across multiple modules. Each Angular application has a root injector, and every NgModule has its own injector. Angular creates a tree of injectors based on the module hierarchy, ensuring that components and services get the correct instances of their dependencies.

Explain the Angular Compiler and its role in the application workflow.

The Angular Compiler is responsible for translating Angular components and templates into JavaScript code that can be executed by the browser. It performs Ahead-of-Time (AOT) compilation, which compiles components and templates during the build process rather than at runtime, resulting in faster startup times and improved performance.

What are Angular Elements and when would you use them?

Angular Elements allow you to package Angular components as custom elements (web components) that can be used in non-Angular applications or frameworks. They provide a way to share Angular components across different projects or integrate them into existing applications without requiring a full Angular environment.

What is Angular CLI and how do you create a new Angular project using it?

Angular CLI (Command Line Interface) is a command-line tool for initializing, developing, and maintaining Angular applications. To create a new Angular project using Angular CLI, you can use the command:

ng new my-project

This command creates a new Angular project named "my-project" with the default project structure and configuration.

Explain Angular directives and give examples of each type.  

Angular directives are instructions in the DOM that Angular uses to manipulate the behavior of elements. There are three types of Angular directives:   Angular directives are instructions in the DOM that Angular uses to manipulate the behavior of elements.

There are three types of Angular directives:

  • Component Directives: These are directives that represent reusable UI components in Angular. 
  • Structural Directives: These are directives that change the structure of the DOM by adding, removing, or manipulating elements. 
  • Attribute Directives: These are directives that change the appearance or behavior of an element by modifying its attributes. 

What is Angular TestBed and how is it used in testing?   

Angular TestBed is a utility provided by Angular for configuring and creating instances of Angular testing modules. It provides methods for configuring modules, components, services, and other dependencies in a test environment. TestBed is used in Angular testing to set up the testing environment, inject dependencies, and create component instances for testing.

Explain Angular Dependency Injection and its benefits.

Angular Dependency Injection is a design pattern used to manage the dependencies between different parts of an Angular application. It allows components and services to request dependencies from a container rather than creating them directly. The benefits of Angular Dependency Injection include:

  • Promotes modularity and reusability of code.
  • Simplifies unit testing by allowing dependencies to be easily replaced with mocks or stubs.
  • Encourages separation of concerns and loose coupling between components.

What is Angular NgZone and why is it used?

Angular NgZone is a service provided by Angular for managing the execution context of asynchronous operations in Angular applications. It is used to explicitly run code outside or inside Angular's zone, which determines when change detection is triggered. NgZone is used to optimize performance and ensure that certain operations are executed within Angular's change detection cycle.

Explain Angular ViewEncapsulation and its modes.

Angular ViewEncapsulation is a mechanism for encapsulating the styles of Angular components to prevent them from affecting other parts of the application. There are three modes of ViewEncapsulation in Angular:

  • Emulated (default): Styles are encapsulated within the component and are scoped to that component's view using unique attributes.
  • Native: Styles are encapsulated using Shadow DOM, a browser technology that provides native encapsulation of styles.
  • None: Styles are not encapsulated and are global to the application, allowing them to affect other components.

What are Angular Services and how are they different from components?

Angular Services are TypeScript classes that encapsulate reusable functionality and provide it to other parts of the application. They are used for implementing business logic, data access, and other common tasks. Services are different from components in that they are not associated with a specific view or UI element. They are singleton instances that are shared across the application and can be injected into components or other services.

Explain Angular Route Guards and give examples of their types.

Angular Route Guards are interfaces that allow developers to control navigation to and from Angular routes. There are several types of Angular Route Guards:

  • CanActivate: Determines whether a route can be activated.
  • CanActivateChild: Determines whether child routes of a route can be activated.
  • CanDeactivate: Determines whether a route can be deactivated.
  • Resolve: Performs route data retrieval before route activation.

What is Angular ng-content and how is it used?

Angular ng-content is a directive used to project content into a component's template. It allows developers to create reusable components with customizable content slots. ng-content is used within a component's template to define where the projected content should be inserted. It supports various projection modes, such as selecting content based on CSS selectors or providing default content.

Explain Angular Observables and their role in asynchronous programming.

Angular Observables are a powerful tool for handling asynchronous operations in Angular applications. They represent streams of data that can be observed over time. Observables are used for handling asynchronous tasks such as HTTP requests, event handling, and data streaming. They support a wide range of operators for transforming, filtering, and combining data streams.

What is Angular ElementRef and how is it used?

Angular ElementRef is a class that provides access to the underlying native element of a component or directive in Angular. It is used to interact directly with the DOM elements within Angular templates. ElementRef is commonly used in conjunction with ViewChild to access DOM elements from within component classes and perform operations such as styling, manipulation, or event handling.

Explain Angular Template-driven Forms and Reactive Forms, and compare their advantages and disadvantages.

Angular Template-driven Forms and Reactive Forms are two approaches for handling forms in Angular applications:

  • Template-driven Forms: In this approach, form controls and validation logic are defined directly in the HTML template using directives such as ngModel and ngForm. Template-driven forms are easier to set up and require less code but are less flexible and harder to test.
  • Reactive Forms: In this approach, form controls and validation logic are defined programmatically in the component class using TypeScript. Reactive forms offer more control and flexibility, support complex validation scenarios, and are easier to test, but require more boilerplate code.

What are Angular Guards and how are they implemented?

Angular Guards are interfaces that allow developers to implement logic to control navigation to and from Angular routes. They are implemented as classes that implement one of the guard interfaces such as CanActivate, CanActivateChild, CanDeactivate, or Resolve. Angular Guards are then registered in the application's route configuration to control access to specific routes or route components.

import { Injectable } from '@angular/core';
import { CanActivate, Router } from '@angular/router';

  providedIn: 'root'
export class AuthGuard implements CanActivate {

  constructor(private router: Router) {}

  canActivate(): boolean {
    // Check if user is authenticated
    const isAuthenticated = true; // Replace with your authentication logic
    if (!isAuthenticated) {
      this.router.navigate(['/login']); // Redirect to login page if not authenticated
      return false;
    return true; // Allow navigation if authenticated

Explain Angular Pipes and give examples of built-in and custom pipes.

Angular Pipes are a feature that allows you to transform data in your templates before displaying it to the user. Angular provides several built-in pipes for common transformations such as formatting dates, numbers, and currency, as well as for filtering and sorting arrays. Additionally, you can create custom pipes to perform custom transformations specific to your application's requirements.

What is Angular NgRx and how does it work?

NgRx is a state management library for Angular applications based on the Redux pattern. It provides a centralized store for managing application state in a predictable and immutable way. NgRx works by maintaining the application state as a single immutable object, using actions to describe state changes, and using reducers to specify how those actions modify the state. It also provides features such as effects for handling side effects and selectors for querying the store.

Explain Angular Forms and their role in data handling and validation.

Angular Forms provide a way to handle user input and perform form validation in Angular applications. Forms in Angular can be template-driven or reactive, and they support features such as two-way data binding, validation,

What is Angular Animation and how is it implemented?

Angular Animation enables adding dynamic motion and effects to elements in Angular apps. Implemented through Angular's animation library, it allows declarative animation definitions using CSS keyframes and JavaScript, enhancing user experience with smooth transitions and visual feedback.

Explain Angular Content Projection and how it is used in component development.

Angular Content Projection allows components to accept and render dynamic content. Developers define slots in component templates with `<ng-content>`, enabling users to inject content into these slots, promoting reusability and flexibility in component development.

What is Angular Change Detection and how does it work?

Angular Change Detection is the process of detecting changes in the application's data and updating the user interface accordingly. It works by comparing the current state of data to its previous state, triggering updates to the DOM as needed to reflect those changes.

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

  selector: 'app-example',
  template: `
    <button (click)="changeMessage()">Change Message</button>
export class ExampleComponent {
  message: string = "Hello, world!";

  changeMessage() {
    this.message = "Goodbye, world!";

Explain Angular Routing and lazy loading of modules.

Angular Routing facilitates navigation between different parts of a single-page app without full page reloads. Lazy loading of modules defers loading non-essential parts until requested, optimizing app performance by reducing initial load time.

What are Angular Pipes and how are they implemented?

Angular Pipes transform data in templates before display. They're applied with the pipe operator (|). Built-in pipes format dates, numbers, and text, while custom pipes enable custom transformations. Pipes are implemented in templates using the pipe operator and can be built-in or custom-defined.

<!-- Template -->
// Component
import { Component } from '@angular/core';

  selector: 'app-example',
  template: `
export class ExampleComponent {
  today: Date = new Date();