Top 20 Angular Interview Questions and Answers

Angular is an open-source JavaScript framework, used to build web applications, single-page applications, web apps and mobile apps. Angular provided a component-based architecture and utilised TypeScript superset to develop applications. Angular provides a structured and efficient development process for creating complex applications and is optimised for performance, suitable to function large-scale applications. As it is maintained by Google, it is in constant maintenance and upgradation by the tech giant to stay relevant.

Here is a list of the top 20 angular interview questions and answers, which will help you to brush up on your basics, and consolidate your foundation.

1. What is TypeScript?

TypeScript is a strongly typed programming language on JavaScript. A superscript of JavaScript, this type of system is easy for Java developers to learn. The type system of TypeScript helps in catching errors during development time, and prevents type-related errors, rather than in running time, thereby, increasing code reliability. Type annotations make code self-documenting rather than requiring separate documentation. Developed by Microsoft, TypeScript is well-suited for large code bases, as it provides better support for code editors.

2. What is Data Binding?

When any internet user can manipulate web page elements using a web browser, this phenomenon is called data binding. This can be done using HTML without using complex scripting or programming. Data binding is usually carried out in web pages with interactive components like calculators, forms, games etc.

3. What is the difference between Angular and AngularJS?

Angular, a JavaScript framework used to develop web applications, is a rewrite of AngularJS. Angular uses component-based architecture, using a statically typed language, TypeScript; whereas AngularJS uses a directive-based framework, using JavaScript. As Angular has a faster change detection mechanism, it is more efficient compared to AngularJS. Angular has a better performance on mobile phones as compared to AngularJS. Angular is regarded as a more updated version of AngularJS, with a more modular architecture and reusing code.

4. Mention some advantages of Angular.

Angular has an improved performance over AngularJS with a more modular architecture, also known as Angular 2+. Certain features to highlight are:
Angular uses component-based architecture, which helps to reuse components and manage the architecture of the application.
The two-way data binding helps in synchronizing the data between the model and the view.
The different components of Angular like pipes, directives, and services help in the smooth creation of applications.
Angular has a large community of developers who contribute regularly to the vast resources.
Angular uses TypeScript which enables class-based object-oriented programming and type inference that facilitates maintaining and debugging.

5. What are directives in Angular?

Directives enable users to write a new HTML syntax in particular for their applications. They are the building blocks of Angular, used to extend HTML vocabulary. They are used to manipulate the DOM elements and add or remove elements. There are three types of directives:

Component Directive
Structural Directives
Attribute Directives

6. What is the PipeTransform interface?

The PipeTransofrm is used to create custom pipes on Angular, to transform data from one form to another. Pipes are responsible to convert data into a more readable format, and numbers into a currency format. The transform method transform() takes in an input value, and yields transformed data. Here is an example of a transformation of string to uppercase format:

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({
name: 'uppercase'
})
export class UppercasePipe implements PipeTransform {
transform(value: string): string {
return value.toUpperCase();
}
}

7. What is an ngModule?

NgModules are containers reserving a block of code to an application domain, taking in metadata objects, and generating an injector at runtime. This class is decorated using @NgModule decorator. Each Angular file must have at least one NgModule, and this class provides a way to structure and manage the code in Angular applications.

8. What are controllers?

A fundamental concept in AngularJS, they are used to control the data and behaviour, of a view, and acted as the intermediary between the view and the model. They are regular JavaScript objects.

9. What is Bootstrap? How is it embedded into Angular?

This is a popular open-source front-end framework, building responsive and mobile-first websites and web applications, providing a collection of CSS and JavaScript components like a navigation menu, buttons, forms and models. If you want to install Bootstrap into the HTML file, then use the following code in the head section.

10. Why were client-side frameworks like Angular introduced?

In order to have a more user-responsive experience, a client-side framework was introduced, and with the use of this framework, web developers can create web applications that are more interactive, and provide a better user response.

11. Explain the concept of dependency injection.

Dependency Injection is a design pattern, and software architecture principle, to manage dependencies between components in an application, and they provide components with services and resources, to perform functions. It becomes easier to test components in isolation, replacing real dependencies, with mock implementations for trial purposes. The main idea is that components should not generate their own dependencies, but should have injected by a third party.

12. What is MVVM architecture?

Model-View-View-Model is used in the development of user interfaces, especially for applications having Windows Protection Foundation. The model represents the logic and business model of the application and acts as an intermediary between the View and the Model.

13. Explain components, modules and services in Angular.

Components, Modules and Services in Angular are three building blocks.
1. Components are the smallest, self-contained units, used to represent UI elements or to view.
import { Component } from '@angular/core';
@Component({
selector: 'app-example-component',
template: `

This is an example component.

`
})
export class ExampleComponent {
constructor() { }
}
2. Modules group together one or more related components, used to provide specific functionality in the Angular application.
import { NgModule } from '@angular/core';
import { CommonModule } from '@angular/common';
import { ExampleComponent } from './example.component';
@NgModule({
declarations: [ExampleComponent],
imports: [CommonModule],
exports: [ExampleComponent]
})
export class ExampleModule { }
3. Services can be injected into any other unit in an Angular application
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root'
})
export class ExampleService {
constructor() { }
getData(): string {
return 'This is some example data.';
}
}

14. What is Eager and Lazy Loading?

Eager loading is the default module-loading strategy, typically used for small-size applications, whereas Lazy loading loads the feature modules when there is a demand.

15. What are template and reactive forms?

In Angular, template-driven forms and reactive forms are two approaches for building and managing forms in a web application.

Template-driven forms are built using the template syntax in Angular, which allows developers to bind form elements to component properties using directives such as ngModel and ngSubmit. This approach is simpler to set up and requires less code than reactive forms, but it is less flexible and harder to unit test.

Reactive forms, on the other hand, are built using a programmatic approach that is based on reactive programming principles. In reactive forms, form controls and validations are defined in the component class, allowing developers to have full control over the behavior of the form. Reactive forms are more flexible, easier to test, and provide a better separation of concerns compared to template-driven forms.

16. How to use ngFor in a tag?

The ngFor directive is used to build lists and tables in the HTML templates, used to iterate over an array or an object, creating a template for each component.

17. What are services in Angular?

They perform tasks used by multiple components, like data and image fetching, database management, and network connections, thus performing all operational tasks of the components, and avoiding rewriting code.

18. Explain the component decorator.

The genre of the class created by TypeScript is decorated using this component decorator, which provides a metadata object, which determines and provides information about the component. Component decorator defines a component and its functions. For example in the following example, @component decorator applied to ‘examplecomponent’ class defines it as ‘app-example’:

@Component({
selector: 'app-example',
template: '

Example Component

',
styles: [`p { font-size: 20px; }`]
})
export class ExampleComponent {
// component logic here
}

19. What is string interpolation in Angular?

This feature allows you to include expressions in a string and is done using double curly braces in the template ( {{ }} ). The expression within these curly braces is evaluated as the value of that expression’s property. It is a convenient way to display dynamic data in the template. This outputs the data from the TypeScript component to the HTML view.

20. What are pure pipes?

A pure pipe is a pipe, called by Angular for reevaluating when it receives a new input value or when the property of an input changes, so if the input value of the pipe remains the same, it will yield the previously calculated risk, and the output doesn’t change as long as the parameters are the same. Angular creates pure pipes by default unless coded otherwise.