49 Angular Interview Questions and Answers [2023]

Are you planning to sit for an interview for the post of Angular Developer? Well, preparing yourself with these Angular interview questions is best.

If you are a JavaScript developer, you might know the Angular framework for front-end development. It has become one of the most in-demand skills for developers in the present world.

However, it can be a bit difficult to have a good understanding of the Angular framework. In such a case, being prepared for anything an interviewer can throw at you is essential. From directives to frameworks, it will help you ace an interview and get the job that can take your career to a new level.

We have sorted some of the most popular Angular interview questions for which you should be prepared to get your dream job.

What is Angular, and Why was it introduced? 

Angular is an open-source JavaScript framework for creating single-page applications. Angular is built using TypeScript and is designed to extend the syntax of HTML. 

Angular was created in 2009 by Miško Hevery, an engineer at Google. He created this framework as a pet project and named it AngularJS, but Google later picked it up. After Google took over the development and maintenance of this framework, it was renamed Angular 2.0, or simply Angular. 

Mention the advantages of Angular. 

• Modular architecture: Code in Angular is grouped into components, making it easy to reuse and rewrite code without changing the entire source code. You can thus build a complex application divided into components with easy-to-read and organized code. 
• Built on TypeScript: TypeScript is a superscript of JavaScript. TypeScript is known for its code quality, making it easy to detect code problems early. 
• Supported by Google: Google is one of the tech world’s big names and has some of the best engineers. 
• Declarative UI: Angular extends the functionality of HTML, which is an easy-to-use language. 
• Supports Progressive Web Apps (PWAs): Angular developers can create Progressive Web Apps that function like mobile apps, lowering costs associated with development. 

Discuss the differences between Angular vs. Angular JS 

Most people use AngularJS and Angular interchangeably. However, the two are different frameworks. 

AngularJS was the first one to be created, and it was built using JavaScript. Miško Hevery created AngularJS, but Google eventually took over its maintenance. Google stopped maintaining AngularJS in January 2022. 

After Google took over AngularJS, it recreated everything from scratch and used TypeScript to create a new framework named Angular 2.0 or just Angular. The new framework introduced a component-based architecture and other enhanced features. 

What is Angular Expression? How are they different than JavaScript Expression?

Angular Expression is a code snippet that coders place in {{ expression }} binding. The significant difference between Angular and JavaScript Expressions are:

• It is easy to use filters before displaying format data.
• Evaluation is forgiving to undefined and null instead of JavaScript undefined that generates ReferenceError and TypeError.
• Evaluated against a scope object.
• Angular Expressions include exceptions, conditionals, and loops.

Give a glimpse into different lifecycle hooks of Angular.

The hooks of the Angular lifecycle are popular when checking triggers and phase changes during the entire duration of a specific phase. The lifecycle component includes the Constructor, which is divided into four major parts: ngOchanges, ngOnInit, ngDoCheck, and ngOnDestroy. ngOchanges are also dining into ngAfterViewInit, ngAfterContentInit, ngAfterViewChecked, and ngAfterContentChecked.

• ngOnchanges( ) – When one (or more) input properties are changed in the components, this method is called. The previous and current values of the properties are received in the hook – SimpleChanges.
• ngOnInit( ) – It comes after ngOchanges to initialize sets input properties and components.
• ngDoCheck( ) – It comes at the third stage to act and detect changes that are impossible with Angular. One can quickly implement a change detection algorithm using this hook.
• ngAfterContentInit( ) – Another hook is to responded after one get content projects in component.
• ngAfterContentChecked( ) – Next is ngAfterContentChecked that is called after every subsequent ngDoCheck and ngAftercontentInit responding after the content projected.
• ngAfterViewInit( ) – The next hook to call is ngAfterViewInit to respond to the child component’s view after the component’s view is checked.
• ngOnDestroy( ) – It helps detach event handlers and clean up the code before Angular destroys the component.

What is the difference between AOT and JIT in Angular?

Many may get confused between AOT and JIT compiler in Angular, and hence it is essential to know the basics:

• Ahead-of-Time (AOT) compiler compiles the code on the server at the build time. At the same time, the Just-in-Time (JIT) compiler is at the run-time in the browser for the application.
• AOT is ideal for production mode, whereas JIT is for development mode that can compile code in Angular project.
• AOT compilation includes ng serve and ng build commands, whereas JIT compilation includes ng serve and ng build CLI commands.
• AOT can reduce bundle size for faster rendering, whereas JIT comes with debugging and implementing major features to map files.

Deep dive into distinct types of Angular filters.

Angular uses a filter to show the users formatting of the expression value that can be added to templates, directives, services, and controllers. One can create personalized filters based on the requirements allowing users to organize data based on criteria. After the pipe symbol ( | ), filters are placed in the expression. The primary filters used in Angular are:

• number – To convert the value into a string
• currency – Converting numbers to currency format
• json – Converting any object to JSON string
• date – Converting it in any date format
• limitTo – Limit the array or string to particular strings or elements
• orderBy – Arranges array in the expression
• uppercase – Converting a string into uppercase
• lowercase – Converting a string into the lowercase
• filter – Select subset from given array

What is view encapsulation in Angular? 

View encapsulation describes template and style encapsulation. Angular has three types of view encapsulation; Emulated, None, and Shadow DOM. Emulated is the default style, where Angular adds a unique attribute to the component’s HTML elements. This approach makes the styling only apply to its view. 

Explain Angular CLI

Angular Command Line Interface, or simply Angular CLI, is a command line tool you can use to create, develop and maintain Angular apps. You can also create and manage workspaces with this tool. You can also generate documentation using Angular CLI.

What is Schematics CLI 

Schematics CLI is built on top of Angular CLI and is used to generate and update code and perform other related tasks for an Angular application. Schematics CLI helps reduce repetitive tasks and has predefined blueprints that ensure code consistency and best practices. 

What is Angular Universal? 

This feature allows Angular applications to be rendered on the server. This technology allows an Angular application to be pre-rendered before sending it to the client/ view. 

What are Angular elements? 

This feature allows developers to package Angular components as web or custom elements. When you transform a component into a custom element, you make all the required Angular infrastructure available to the browser. 

Discuss Angular authentication and authorization

Authentication verifies the identity of the user. The user is expected to provide an email/username and a password. If authentication goes through, the user is granted access to the application.

Authorization refers to the process of denying or giving access to the application resources based on the presented credentials. 

Define bootstrapping.

Bootstrapping is a way to start or initialize the application in Angular, whether automatically or manually. Let us help you understand it in a better way:

• Automatic bootstrapping is included when adding ng-app directives on the tag if required. Angular compiles the DOM and is associated with the module finding ng-app directive.
• Manual bootstrapping is to initialize the Angular app and offer control to the developers to perform significant operations and tasks to compile the page.

Throw some light on Angular directives.

When it comes to Angular directives, there are three significant kinds such as:

• Attribute – Using this, one can change the behavior and appearance of elements, another directive, and components. It uses ngStyle and ngClass as the attributes of elements.
• Components – It consists of templates that can define a single user interface using CSS styles, TypeScript code, and HTML template. It is usually decorated with @ symbol giving an angular compiler to replace it with the component templates.
• Structural – It changes the view structure to hide or show some data using different directives such as ngIf directives.

What is TypeScript?

TypeScript is a strongly typed programming language. It is a superscript of JavaScript built on top of JavaScript. Thus, it offers all the functionalities of JavaScript and introduced types, allowing developers to catch bugs before they move to production. 

What are single-page applications? 

Single-page applications are applications that have a single HTML page. SPAs dynamically update the web page’s content as the user interacts with the application without reloading the entire application. Angular is an example of a framework that creates SPAs. 

What are annotations? 

Annotations are blocks of text that can be displayed over a connector or a node. These functions can be attached to methods, properties, or classes to provide additional configuration or modify their behavior. To write an annotation, start with the @ symbol before the target element you are decorating. 

What are components? 

Components are the basic User Interface building blocks of an Angular app. These components have HTML, CSS, and TypeScript that define how a part of the UI should look and behave. 

Explain RxJS.

Reactive Extensions for JavaScript (RxJS) uses observables allowing developers to perform reactive programming. The aim is to compose callback-based code or asynchronous operations using the RxJS framework in Angular.

It can help in streaming data to subscribers emitting values from publishers. If you are not using Angular, other programming languages, such as Python and Java, can use observables using reactive code.

What are dynamic components?

Dynamic components are components that can be created and rendered at run-time. Dynamic components are created dynamically, unlike their static components that are declared in markup or defined in templates. You can use dynamic components to create dynamic menu systems, dynamic chat systems, and so much more. 

Explain data binding.

Data binding is considered one of the most influential and essential features that can establish a connection between components and DOM. It is simple to define the process of interactive applications without worrying about pulling and pushing the templates and components. Several types of data binding are used in Angular, such as

• Property binding,
• Two-way data binding,
• Event binding, and
• String interpolation.

What are pipes? 

Pipes are functions that take an input value and return a transformed value. You can use pipes to transform currency amounts, dates, or strings. 

What are pure pipes and impure pipes? 

Pure pipes are pipes whose output is determined by the inputs. Angular pipes are pure by default and only called when a change is noted in the inputs. 

Impure pipes are called any time there is a change in the cycle. However, that change does not necessarily have to be on the inputs. Impure pipes depend on the external state, such as your location or time. 

What is PipeTransform Interface? 

A PipeTransform Interface is a built-in interface that accepts input value and returns a transformed value. In Angular, the transform method, transform(), is invoked with the value of the binding as the first argument and other parameters as the second argument in a list form. 

What are promises and observables? 

Promises in Angular are unicast, meaning they will be executed only once, even if you call them multiple times.

Observables in Angular are multicast, meaning they will be executed every time you subscribe to an observable. 

What are controllers? 

Controllers are only available in AngularJS. However, Angular uses components. Controllers are one of the parts of the MVC architecture of AngularJS. Controllers in AngularJS define specific UI parts’ behavior and logic. 

What is string interpolation? 

String interpolation allows users to display dynamic data to the end user (on the HTML template). This one-way binding technique transfers data from TypeScript code to an HTML template or view. String interpolation uses double curly braces ({{}}) to display data from the component to the view. 

What is lazy loading? 

This feature allows you to load JavaScript components when a specific route is activated. This approach can improve your app’s performance as it does not load everything at a go. 

What is a FormBuilder? 

FormBuilder is a utility class that offers various ways to create FormControl, FormGroup, or FormArray. This utility class reduces the amount of Angular boilerplate needed to create complex forms. 

What are reactive forms? 

Reactive forms are forms whose state is managed programmatically. These forms offer access to information about a given control through methods and properties provided by each instance. Reactive forms are flexible, powerful, and easy to test. 

What are decorators? 

Decorators are functions or features that allow adding metadata to a method, class, parameter or property. Decorators can modify or enhance the behavior of a method, class, parameter or property at design time. We use @ symbol before the decorator. 

What are property decorators? 

Property decorators are applied to class properties to modify their behavior or metadata. A perfect example of a property decorator is @Input decorator, which allows the property to get/ receive values from the parent. 

What are class and method decorators? 

Class decorators are applied to classes in Angular. Examples of class decorators are @Component, @NgModule, and @Directive. 

Method decorators are applied to methods within a class. Examples of method decorators are @HostListener and @ViewChild. 

What is property binding? 

It is a one-way mechanism that allows users to set the property view of an element. Property binding allows you to control the behavior and appearance of the components dynamically. 

What is 2-way binding? 

This mechanism allows users to bind a component property and an HTML element property. 2-way binding allows your components to listen for events and update values dynamically between child and parent components. 

What are template expressions? 

These are expressions that are evaluated and displayed in the template. Template expressions are used to display dynamic content, such as the result of a calculation or the value of a property. 

What are template statements? 

Template statements are properties/ methods you can use in your HTML code to respond to user events. Such events include mouse movement, form submission, or button clicks. 

What are modules? 

In Angular, a module is a container that groups together related components, services, pipes, and directives that work together in an application. The modularity system in Angular is known as the NgModule. 

What is the state function? 

You can use the state() function to define different states you can call at the end of each transition. A state() function takes two arguments; a unique name, that is; closed or open, and a style() function.

What is the style function? 

A style function declares a value/ key object containing CSS styles/ properties that can be used for an animation state within an animation sequence. 

What is multicasting? 

It is the practice of using a single execution to broadcast to a list to multiple subscribers. To achieve this, you use a multicasting observable, meaning you don’t have to register multiple listeners on your document, as you can re-use the first listener and send values to all subscribers. 

What are the different types of events that can be triggered in the Angular router? 

There are different events, but we will mention a few.

NavigationStart: Triggered when the router starts navigating a new route. 

NavigationEnd: Triggered when the Angular router finishes navigation of a new route. 

NavigationError: Triggered when the router encounters an error during navigation. 

What are router links? 

Router links in Angular are used to navigate between different components or views in an application using the Angular Router module. 

You can have a route that navigates to the “home” route as follows;

<a routerLink="/home">Home</a>

Explain dependency injection 

Dependency injection is a concept in Angular that allows classes with Angular decorators like Injectables, Directives, Components, and Pipes to configure the dependencies they need. This concept facilitates interaction between dependency providers and dependency consumers through the Injector abstraction. 

Explain MVVM architecture 

MVVM is the short form for Model-View-ViewModel. 

• Model: This represents the data and business logic of the Angular application.
• View: This represents the user interface. 
• ViewModel: This acts as the intermediary between the model and the view. Components in an Angular application correspond with the ViewModel. 

Discuss differences between structural directives and attribute directives 

Structural directives are used to add elements or remove elements from the DOM. structural directives have a * symbol before their names. Examples are *ngFor, *ngIf, and *NgSwitch. 

Attribute directives are used to modify the appearance or behavior of DOM elements. To use these directives, you must add square brackets [] before them. 

Explain how custom elements work

The custom elements feature allows you to create a reusable Angular component and reuse it in other frameworks supporting web components. For instance, you can create a custom element named home-button that renders a button with Angular functionality. Later, you can reuse this home-button in your HTML code like regular HTML. 

 How do components share data in Angular? 

• Parent-to-child: Use the @Input() decorator to share data from parent to child. 
• Child-to-parent: Use the @output() decorator to share data from child-to-parent components. 
• Shared service: You can inject a service to both parent and child components and then use it to share data. 
• ViewChild: You can access a child component from the parent component using the ViewChild decorator. 

Conclusion

These are the essential questions and answers usually asked in Angular interviews. It will help you prepare for the interview, ace it, and get your dream job.

If you are done with this, know more about AngularJS.