Angular Test Questions

Question 1

What is Angular, and how does it differ from AngularJS?

Answer 1

Angular is a popular open-source web application framework for building dynamic, single-page applications. It is developed and maintained by Google and a community of developers. Angular is often used for building modern, interactive web applications with a rich user interface.

Angular differs significantly from AngularJS, its predecessor, in several key aspects:

Language - TypesScript instead of JavaScript

Architecture - Angular JS follows an MVC architecture, whereas Angular uses a component-based architecture.

Mobile Development - Angular is designed with mobile development in mind, offering features for building responsive and mobile-friendly web applications.

Change Detection -
Dependency Injection - Angular JS relies on a two-way data binding mechanism, which can be less efficient for applications with a large number of data bindings.

Performance - Angular offers improved performance and loading times due to its optimized rendering engine, lazy loading, and AOT compilation.

Directives - In Angular, directives are move powerful and flexible, and they allow you to manipulate the DOM and create custom structural directives.

Tooling - Angular provides a command-line interface (CLI) that simplifies project setup, development, and deployment. AngularJS doesn’t have a similar toolset.

Community and Ecosystem - Angular has a larger and more active community, with extensive third-party libraries, components, and tools.

Long-term Support - Angular follows a regular release and offers long-term support (LTS) versions, ensuring ongoing updates and security patches. AngularJS is no longer actively developed or supported.

Question 2

Explain the key features and benefits of Angular

Answer 2

• Component-Based Architecture
• TypeScript
• Two-Way Data Binding
• Dependency Injection
• Directives
• Routing
• HTTP Client
• Forms and Validation
• Observables
• Ahead-of-Time (AOT) Compilation
• Command-Line Interface (CLI)
• Cross-Platform Development
• Community and Ecosystem
• Long-Term Support (LTS)
• Testing
• Security
• Internationalization (i18n)

Question 3

What is TypeScript, and why is it used in Angular?

Answer 3

TypeScript is a statically typed superset of JavaScript that compiles to plain JavaScript. It’s used in Angular for:

• Static Typing
• Code Maintainability
• Enhanced Tooling
• Type Safety
• Interfaces
• Class-Based Programming
• ES6+ Features
• Integration with Existing JavaScript
• Excellent Angular Integration
• Community and Adoption

Question 4

Describe the components in Angular and how to create one.

Answer 4

In Angular, a component is one of the core building blocks of the application’s user interface. Components are responsible for defining the structure, behavior, and appearance of a part of the application’s UI. Components are based on the concept of a Shadow DOM, which means they have their own encapsulated view and styles, making it easier to build and maintain complex web applications.

You can generate a component in Angular by using the Angular CLI. ng generate component my-component-name.

To use the component in your application, include it in the template of another component or add it to the routing configuration if it’s a part of a specific route. For example, if you want to use ‘my-component’ in another component’s template, you can simply include it using the component selector, like this:

<app-my-component></app-my-component>

Question 5

What is the Angular CLI, and how is it used in Angular development?

Answer 5

The Angular CLI (Command Line Interface) is a powerful tool that helps developers create, manage, and build Angular applications more efficiently. It provides a set of commands to streamline common development tasks and ensure best practices are followed. Here are some key aspects of the Angular CLI and how it is used in Angular development:

Project generation - ng new my-angular-app

Project Structure - the CLI generates a predefined project structure, including components, services, modules, and other files, following Angular best practices. This structure helps maintain consistency across projects.

Development server - ng serve

Code generation - ng generate

Testing - ng test

Build - ng build

Linting - ng lint

Configuration

Multiple Environment Support

Third-Party LIbrary Integration - ng add @angular/material

Update Angular Versions - ng update @angular/core@latest

Question 6

Explain the Angular module and its purpose

Answer 6

An Angular module is a mechanism for organizing an application into cohesive blocks of functionality. It consists of a TypeScript class annotated with the @NgModule decorator. Modules encapsulate components, services, directives, and other code related to a specific feature or functionality. The main purposes of Angular modules include:

Code Organization: Modules help organize code into manageable and reusable units.
Dependency Management: Modules define the dependencies of the application, making it clear which components and services are available.
Encapsulation: Modules encapsulate related functionality, preventing naming conflicts and promoting code separation.
Lazy Loading: Modules support lazy loading, allowing parts of the application to be loaded on-demand for better performance.

Question 7

Differentiate between declarations, providers, and imports in an Angular module.

Answer 7

Declarations: Lists the components, directives, and pipes that belong to the module. Angular uses this information to understand which components are part of the module.

@NgModule({
declarations: [MyComponent, MyDirective, MyPipe],
})

Providers: Specifies the services that the module contributes to the global collection of services. Services listed here are available for injection across the entire application.

@NgModule({
providers: [MyService],
})

Imports: Lists other modules whose exported components, directives, or pipes should be available to templates in this module.

@NgModule({
imports: [CommonModule, FormsModule],
})

Question 8

What is data binding in Angular, and what are the different types of data binding?

Answer 8

Data binding in Angular is a way to establish a connection between the application’s data and the user interface. There are four types of data binding:

Interpolation ({{ expression }}): Binds the expression’s value into HTML text content.

<p>{{ title }}</p>

Property Binding ([property]=”expression”): Sets the property of a target HTML element to the value of the expression.

<img [src]=”imageUrl”>
Event Binding (event)=”expression”: Listens for events on the target element and executes the expression when the event occurs.

<button (click)=”handleClick()”>Click me</button>
Two-Way Binding ([(ngModel)]): Combines property binding and event binding to achieve two-way communication between the component and the view.

<input [(ngModel)]=”username”>

Question 9

How do you create a two-way data binding in Angular?

Answer 9

To create two-way data binding in Angular, you can use the [(ngModel)] directive. This directive combines property binding (to update the view) and event binding (to update the model). Ensure that you have the FormsModule imported in the module where you use two-way binding.

<input [(ngModel)]=”propertyName”>
In the corresponding component, you should have a property named propertyName:

import { Component } from ‘@angular/core’;

@Component({
selector: ‘app-example

Question 10

What are directives in Angular, and how do they differ from components?

Answer 10

Directives in Angular:

Directives are instructions in the DOM (Document Object Model) that Angular uses to manipulate and extend HTML.
They are markers on a DOM element that tell Angular to run or reference some behavior.
Examples include structural directives (e.g., ngIf, ngFor) and attribute directives (e.g., ngStyle, ngClass).
Difference from Components:

Components are directives with a template. A component brings together HTML, CSS, and JavaScript logic in a single file.
While components have a view associated with them, directives are more about behavior and manipulation of the DOM.

Question 11

What is dependency injection in Angular, and why is it important?

Answer 11

Dependency Injection (DI):

Dependency Injection is a design pattern in which components are given their dependencies rather than creating them.
In Angular, the DI system provides services and other dependencies to components as requested.
It enhances modularity, testability, and maintainability by promoting loose coupling between components.
Importance:

Encourages the development of loosely coupled and easily testable components.
Promotes the reuse of services across multiple components.
Simplifies the process of providing mock services during testing.

Question 12

How does Angular handle routing, and what is a router outlet?

Answer 12

Angular Routing:

Angular provides a powerful router module for building single-page applications with navigation.
The router enables navigation between views and allows for loading components on-demand.

Router Outlet:

The <router-outlet> is a directive provided by the Angular Router that acts as a placeholder where the component corresponding to the active route is displayed.
It marks the spot in the template where the component view should be inserted.</router-outlet>

Question 13

Describe Angular services and their role in an Angular application.

Answer 13

Angular Services:

Services in Angular are singleton objects created to perform tasks and provide functionality throughout the application.
They encapsulate reusable and shareable logic such as data fetching, authentication, or business logic.
Services are typically injected into components via Dependency Injection.

Role:

Encapsulate business logic and data manipulation.
Provide a centralized way to manage application state.
Promote code organization and maintainability.
Enable code reusability across components.

Question 14

What is an Angular pipe, and how is it used to transform data?

Answer 14

Angular Pipe:

An Angular Pipe is a way to transform data in a template before it is displayed in the view.
Pipes can be used for tasks like formatting dates, converting text to uppercase, or filtering lists.
Usage:

{{ data | pipeName:param1:param2 }}
15. Explain the concept of observables and how they are used in Angular.
Observables:

Observables are a part of the Reactive Extensions for JavaScript (RxJS) library and are used to handle asynchronous operations.
They represent a stream of data over time, allowing for handling events, asynchronous requests, and more.

Usage in Angular:

Observables are widely used in Angular for managing asynchronous tasks, such as HTTP requests.
They can be subscribed to, and Angular’s HttpClient returns observables for handling HTTP responses.

Question 15

What is lazy loading in Angular, and why is it beneficial?

Answer 15

Lazy Loading:

Lazy Loading is a technique where modules or components are loaded on-demand rather than upfront when the application starts.
It improves initial loading time by deferring the loading of non-essential parts of the application until they are needed.

Benefits:

Faster initial page loads for large applications.
Reduced bandwidth usage as only necessary code is loaded.
Better user experience by focusing on essential functionality first.

Question 16

How does error handling work in Angular applications?

Answer 16

In Angular, error handling involves capturing and responding to errors during the execution of an application.

Angular provides mechanisms for handling errors in components, services, and HTTP requests.

Error Handling Approaches:

Try-Catch: Use standard try-catch blocks for synchronous code.

Observable Error Handling: For asynchronous operations, observables handle errors through the error callback in the subscribe method.

Global Error Handling: Angular provides a global error handler to capture unhandled errors.

Question 17

Describe the Angular change detection mechanism and its types.

Answer 17

Change Detection:

Change Detection is the process of identifying and updating the parts of the application affected by a change in state.
Types:

Default (Zone.js): Angular uses Zone.js by default for change detection. It automatically triggers change detection after browser events and XHR requests.

OnPush: Change detection only occurs when input properties to a component change or when events are triggered. It can be explicitly set using changeDetection: ChangeDetectionStrategy.OnPush in component metadata.

Question 18

What is AOT (Ahead-of-Time) compilation in Angular?

Answer 18

AOT Compilation:

AOT compilation is a build process that compiles Angular applications during the build phase rather than at runtime.
It converts Angular templates and components into highly optimized JavaScript code before deploying the application.

Benefits:

Faster rendering in the browser as there’s no need for template compilation at runtime.
Smaller bundle sizes, reducing the size of the application files sent to the client.

Question 19

Can you explain Angular decorators and provide some examples?

Answer 19

Angular Decorators:

Decorators are functions that modify the behavior of JavaScript classes or properties.
In Angular, decorators are used to mark classes and properties as Angular components, services, modules, etc.
Examples:

@Component: Decorates a class as an Angular component.

@Component({
selector: ‘app-example’,
template: ‘<p>Hello, World!</p>’,
})
export class ExampleComponent { }
@Injectable: Decorates a service class to indicate that it can be injected as a dependency.

@Injectable({
providedIn: ‘root’,
})
export class ExampleService { }

Question 20

How to perform unit testing in Angular using tools like Jasmine and Karma?

Answer 20

Jasmine: A behavior-driven development (BDD) framework for writing unit tests.
Karma:

Question 21

What is a decorator in Angular?

Answer 21

In TypeScript and Angular, decorators are used to annotate and modify classes and their members. The @Component decorator is specifically used to mark a class as an Angular component.

import { Component } from ‘@angular/core’;

@Component({
selector: ‘app-root’,
templateUrl: ‘./app.component.html’,
styleUrls: [’./app.component.css’]
})
export class AppComponent {
// Component logic and properties go here
}

Decorators like @Component play a crucial role in Angular applications by providing metadata and configuration to the Angular framework, allowing it to understand and manage components effectively.

Question 22

What is ngOnInit

Answer 22

A lifecycle hook in Angular that is called after Angular has initialized all data-bound properties of a directive

export class RecipeDetailComponent implements OnInit {
// Other class members…

ngOnInit() {
// Implementation for ngOnInit goes here
}

// Other class members…
}

Question 23

What is an Angular directive?

Answer 23

A directive tells the framework to do something to a DOM element. There are 3 main types of directives:

1. Components
   - controls a part of the user interface and is typically associated with a custom HTML element
   @Component({
   selector: ‘app-my-component’,
   template: ‘<p>This is my custom component!</p>’,
   })
   export class MyComponent {}
2. Structural Directives
   - change the structure of the DOM by adding, removing, or manipulating elements. Identified with an asterisk (*) prefix in the HTML
   <!-- Example of *ngIf -->

<div *ngIf=”isUserLoggedIn”>Welcome, User!</div>
<!-- Example of *ngFor -->

<ul>
<li *ngFor="let item of items">{{ item }}</li>
</ul>

3. Attribute Directives
   - change the appearance or behavior of an element, component, or another directive. They’re applied to elements as attributes
   <!-- Example of ngStyle -->

<div [ngStyle]=”{ ‘color’: textColor, ‘font-size’: fontSize }”>Styled Text</div>
<!-- Example of ngClass -->
<div [ngClass]=”{ ‘highlight’: isHighlighted, ‘italic’: isItalic }”>Stylized Text</div>

Question 24

What is a service in Angular?

Answer 24

A class that encapsulates a specific functionality or feature and can be shared across components.

Services in Angular are used to organize and centralize code that doesn’t belong to a specific component but is needed across the application.

Key characteristics and uses of Angular services:

• Singleton Instances
• Dependency Injection
• Separation of Concerns
• Reusability
• Promoting Code Organization

Question 25

What is a dependency injection?

Answer 25

A dependency injection allows you to inject dependencies, such as services, into components, services, or other objects.

To create a dependency injection, first you create your dependency (in a typescript class):

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

@Injectable({
providedIn: ‘root’,
})
export class DataService {
getData(): string {
return ‘This is data from the DataService’;
}
}

And then you inject the dependency by doing:

// app.component.ts
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) {
// Use the injected DataService to get data
this.data = this.dataService.getData();
}
}

Inside the constructor, we use the injected ‘DataService’ to get some data. This is an example of how Angular injects dependencies into components.

Angular takes care of creating and managing the instances of services and injecting them where they are needed. This makes the application more maintainable in general.

Question 26

What is a singleton service in Angular?

Answer 26

A service that is instantiated only once per application and shared across the entire application. This means that there is only one instance of the service in the entire Angular application, regardless of how many times it is injected into various components, directives, or other services. Here’s an example:

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

@Injectable({
providedIn: ‘root’,
})
export class DataService {
// Service implementation here
}

In this example, the @Injectable decorator is used to indicate that DataService is a service.

And the providedIn: ‘root’ property in the decorator specifies that Angular should provide this service at the root level, making it a singleton.