60+ Top Angular Interview Questions and Answers

Angular has become one of the most popular frameworks for building front-end web applications . As such, it is usually a hot topic in web development job interviews. This set of Angular interview questions will certainly be helpful to clear your interview. But before we get into that, let us quickly recap about Angular .

What is Angular?

You would think, Ah… yet another web framework to learn, but Angular is not like other web frameworks; it is genuinely different. You will enjoy learning this TypeScript-based open-source front-end web application framework.

Before we tell you more, let us clear that Angular is different from AngularJS but has been put together by the same Google team behind AngularJS.

Initially developed as a Single Page Application (SPA), better tools for JavaScript like React and Vue were released, so Angular had to be made into something more – if it was to be what it is today!

This frontend framework has loads of reusable and robust components, and you can write clean, maintainable code with that. In 2018, Angular was ranked as the second most used technology, the first one being Node.js . The real power of Angular came with its version 4, which offered a galore of features, including:

• Backward compatibility,
• Faster compilation,
• More reusability leads to writing less code,
• Better libraries for HTTP requests, and
• Conditional disabling of animations.

Angular is based on HTML , CSS , and TypeScript and is a great platform for building both desktop and mobile applications. Wait… what?

But I recently read somewhere that browsers do not support TypeScript! Yes, TypeScript is converted into another language ( JavaScript ). This process is called transpilation (and not compilation). Angular is also called Angular 2+. Since Angular is based on TypeScript, it accommodates all the features of JavaScript as well as TypeScript.

Angular interview questions help aspirants crack a web development job interview and get their dream job.

Why Angular?

Now comes the critical question; Why Angular? Because Angular comes with a range of benefits and features that are apt for enterprise applications and websites that have a lot of dynamic content or multiple workflows.

Whether it is exhaustive documentation, extensive support by Google, or component-based architecture (from version 2), Angular has all you can expect from a web development framework .

Some best reasons to use Angular are:

• Support from Google, thus, making the platform user-friendly and trustworthy.
• A component-based architecture where the application is divided into functional and logical components that are independent of each other. Parts can be decoupled, replaced, or reused easily. This type of architecture also ensures easier testing at each stage.
• A lot of reusable code and third-party components are available, thus improving productivity.
• Faster code rendering because it gets converted from TypeScript (or HTML) to JavaScript during the build process itself. This is called Ahead-of-Time (AOT) compilation.
• Features a command-line interface (CLI). It facilitates development in the most efficient way. You can create a new project, add your functionalities, and test them quickly. Further, initialization and configuration become easy too.
• Angular 6 allows adding custom elements to web apps built with other environments like React, Vue, and jQuery. It also includes an Ivy renderer that translates components and templates into JavaScript by rendering. During the process, any unused code is removed, thus making web apps load faster.
• Angular Universal for server-side rendering helps increase the number of users on the website and makes webpage loading faster.
• Excellent documentation and community support.

How to Crack an Angular Interview?

Angular is very easy, and if you have hands-on experience, you will be able to answer most of the interview questions based on the popular web framework. As a sigh of relief, there are no tricky questions in Angular.

In the Angular interview, you may expect some questions about TypeScript as well. Additionally, you can share your experience of working with Angular. Sometimes, there may be subjective questions, like what other technologies have you worked with, comparison between two techniques built for the same purpose from your perspective (for example, which one was more comfortable? or which one had a better learning curve?), or even your personal opinion about your favorite technology out of the ones you have worked with so far.

The answer depends on your individual experience, and this is where you can gain that extra edge. The more personalized experience you share, the more interested the interviewer will be in asking you further Angular interview questions. The Angular interview questions and answers below are purely technical, and sometimes your answer will naturally lead to the next question.

These Angular interview questions can also be useful in Angular 5 interview questions, Angular 6 interview questions, Angular 7 interview questions, and Angular 8 interview questions.

Top Angular Interview Questions and Answers

For a better experience, we have divided the list of Angular interview questions into three levels, namely basic, intermediate, and advanced.

Basic-level Angular Interview Questions

1. What is Angular? (or What do you know about Angular?)

Answer: If you have mentioned Angular in your resume, indeed, this will be the first Angular question of every interviewer. Angular is an open-source, front-end web development framework based on TypeScript. It is most suited for developing enterprise web applications because the code is reusable and maintainable.

Angular started as a SPA (single-page application) framework and now supports dynamic content based on different users through dependency injection. YouTube TV is one of the most popular companies that use Angular.

2. What is the purpose of Angular?

Answer: The purpose of using Angular is to create fast, dynamic, and scalable web applications with ease using components and directives.

3. What are the essential building blocks of Angular?

Answer:

1. Components : The concept of Angular is based on Components, which are the basic building blocks. Components follow a tree structure where the App component is the root component. A component encapsulates the logic of the view, data, and HTML markup. Every app must have at least one part. The more the parts of smaller size, the better the code readability is.
2. Modules : The module, the second most crucial building block, is a container that groups related components. The default module in an application is the app module. Blades should be small in size and have related components.

Other essential building blocks of Angular are:

• Templates: Templates are written in HTML and contain Angular elements and attributes. Models provide a dynamic view to the user by combining information from the controller and view and rendering it.
• Directives: Directives allow developers to add new HTML syntax, which is application-specific. The behavior is essentially added to the existing DOM elements.
• Services: Rather than calling the Httpservice, Angular allows for the creation of new service classes. When new Services are created in Angular, they can be used by different components.

4. What is the difference between Angular and AngularJS? (Angular vs AngularJS)

Answer: The following table highlights the differences between Angular and AngularJS:

5. Mention some of the features of Angular.

Answer: The following are the important features of Angular:

• Follows a component-based architecture. Hence, applications are written as a set of independent components.
• Parts can be created, tested, and integrated using the Angular CLI.
• Great support for complex animations without writing much code.
• Because of the component router, Angular supports automatic code-splitting. Hence, only the code required to render a particular view is loaded.
• Cross-platform application development.
• Template syntax for creating UI views.

6. Discuss some advantages of using Angular.

Answer: There are many advantages apart from the fact that Angular gives us a break from the MVC pattern, as it follows a component-based structure. The following are some critical benefits of using Angular:

• Supports two-way data binding.
• Supports validations and template syntax (both angular and static).
• We can add custom animations, directives, and services.
• The event handling process is seamless.
• Hierarchical Dependency Injection structure (Parent-child).
• Provision to facilitate RESTful services and client-server communication.

Note : As a follow-up, the interviewer(s) may ask you more about any of the above advantages. One or two lines should be sufficient. We will answer each as you read further questions.

7. Can you think of any disadvantages of using Angular?

Answer: Not as a disadvantage, but in some scenarios, Angular may not be the right fit. For example, short-term projects or lightweight websites that have more static content do not require the complex Angular framework. Same way, apps that have a microservice design approach will find too many unused features if they use Angular since it is a complete solution. Also, there is less flexibility for the developer to choose additional tools.

8. What is Angular CLI? How do you use it?

Answer: Angular CLI automates the end-to-end development process. The app's initialization, configuration, and development process become straightforward. With a command-line interface, we can create a new project, add new features, and run tests (unit tests and end-to-end tests) by just typing a few simple commands. This way, both development, and testing processes become faster. For example, To create a new application, we should type:

ng new <appname> [options]

For creating a class using CLI (in Angular 7), we have to type:

ng generate class MySampleClass [options]

To generate a component:

ng g c <componentname>

9. What are directives in Angular?

Answer: With directives, developers can write application-specific custom HTML syntax. The new language is written in the DOM, and the Angular compiler executes the directive functions when it finds a new HTML syntax. There are three types of Angular directives – attribute, component, and structural.

10. Mention an example of the structural directive.

Answer: Structural directives change the structure of DOM. Examples, *ngIf and *ngFor. Usage example:

<div *ngIf = “product” class=”name”>{{product.name}}</div>

Same way:

<ul>
<li *ngFor = “Show product list”>{{product.name}}</li>
</ul>

11. How is Dependency Injection (DI) done in Angular?

Answer: In Angular, a class asks for services or objects when it is instantiated. This means if a class is invoked, it doesn’t create any objects. Rather, it depends on an external source to instantiate objects, services, or parameters. In this process, an injectable service is created and registered. You can configure injectors in the following three ways:

1. @Injectable() decorator for the service.
2. @NgModule for NgModule.
3. @Component for the component.

12. What are templates in Angular?

Answer: The template is simply an HTML view where binding controls can display data to the properties of the Angular component. Templates can be defined inline using the template property as: template:

<div>My sample Template</div>

Or can be called from a different HTML file by using @Component decorator’s URL property:

templateUrl: 'app/app.component.html'

13. How are Angular expressions different from JavaScript expressions?

Answer: Both are similar and can have operators, variables, and literals. However, there are a few differences that the following table highlights:

14. Explain the architecture of Angular.

Answer: As we have seen in the second question on this list of Angular interview questions, components, modules, templates, and so forth are the main building blocks of Angular. All of these are based on modules, which provide compilation context for components. When asked in the interview, you can talk about the essential building blocks and then draw this Angular architecture diagram to depict the relationship between each building block of Angular. You can see that the view is contained in the template, and properties are bound from components to the template. The DI services are injected by the injector into the parts as required. Directives are added to the model. Modules contain the core logic, like services, values, functions, and components.

15. Tell us some differences between components and directives.

Answer: An Angular component is a specific type of directive that has a view. The following table draws the major differences between components and directives in Angular:

16. Which language does Angular use primarily?

Answer: Angular primarily uses TypeScript and HTML. The latter is used for the template, and the former is used for components.

17. What is the latest version of Angular ?

Answer: The latest stable version of Angular is 12.1.4. It was released in July 2021.

18. What is data binding, and what are the different categories of data binding?

Answer: Data binding is used to connect the application data and DOM, i.e., components with the template. They can be categorized based on the direction of the data flow. The following table describes different categories of data binding:

19. Explain the differences between one-way binding and two-way binding.

Answer:

20. Which different filters does Angular support?

Answer: The following table highlights the filters that Angular supports, along with their descriptions:

Note : In the interview, you can mention a few of them and give an example as well:

<p>Amount: {{ amount | currency }}</p>

21. What are NgModules? Differentiate between Javascript modules and NgModules.

Answer: NgModule was introduced after Angular 2 to enable developers to declare all the relationships in one place with metadata. Thus, in short, NgModules are built from metadata that describes components, services, directives, pipes, and so on. Angular then creates a component factory, which is a class that creates components. Differences between JS modules and NgModules are as follows:

22. What are ngIf and ngFor? Can you show a small example to use them?

Answer: ngIf and ngFor are Angular versions of if and for control statements, respectively. Example:

<p *ngIf="display">Show this only if the Boolean "display" is true</p>

Where the display is a Boolean value. ngFor allows looping through and displaying elements of an array. Example:

<tr *ngFor="let student of students; let i = index">
<td>{{student.name}}</td>
<td>{{i}}</td>
</tr>

The second part (i=index) is optional and only needed if you want to display the index.

23. What are the new features in the latest version of Angular?

Answer: The latest version is Angular 11.2.5 , and the following are some of its important features:

• Support for TypeScript 3.4.
• Dynamic import for lazy routes.
• Web workers.
• Differential loading for application code.
• Introduction of Angular Ivy – improved payload size, backward compatibility, faster re-build time, easier debugging, and so on.

24. What is a component?

Answer: The component is a logical piece of code. It consists of a template (that contains the HTML or URL that requires rendering), a class (that defines properties and methods that supports the view), and metadata (defined using a decorator). Example:

@Component ({
selector: 'my-app',
template: ` <div>
<h1>{{appTitle}}</h1>
<div>What is your name?</div>
</div>,
})

25. Is there a way to convert Typescript code into JavaScript code?

Answer: Yes, there is a way to convert TypeScript code into JavaScript code. We call it transpilation.

26. What is the digest cycle?

Answer: The digest cycle is the process of monitoring the watchlist to track the changes in the value of the watch variable. It is implicitly triggered, but we can also trigger it manually using the $apply() function.

27. What is a pipe? Write a simple code to demonstrate.

Answer: Pipe (|) enables us to transform input data into the desired format. For example:

<p>Price is {{ price | currency }}</p>

28. Can you create a parameterized pipe in the above example?

Answer: Yes, we can create a parameterized pipe using the following code:

<p>Price is {{ price | currency : “USD$” : 0.00 }}</p>

29. Explain how you can chain pipes?

Answer: We can add any number of filters using pipes. For example:

<p>Average is {{ average | uppercase | number}}</p>

30. Is it possible to create a custom pipe? How?

Answer: Yes, we can create custom pipes.

• Pipe metadata @Pipe decorator can be imported from the core Angular library.
• The pipe is a class that is decorated with the above metadata (@Pipe({name: 'myCustomPipe'})).
• The next step is to define the transformation. For this, the pipe class should implement the transform() method of the Pthe ipeTransform class.
• Specify the pipe name in the main code.

Example:

<p>Size: {{number | myCustomPipe: 'Error'}}</p>

Intermediate-Level Angular Interview Questions

31. What is the purpose of an async pipe?

Answer: Async pipe subscribes to a promise or an observable and returns the latest value. If a new value is emitted, the pipe marks the component that needs to be checked for any changes. Example:

<code>observable|async</code>

32. What is the difference between pure and impure pipes?

Answer: The following table outlines the differences between pure and impure pipes:

33. Explain the importance of HttpClient.

Answer: HttpClient is a simplified HTTP API for Angular applications. It gives better observable APIs, better error handling mechanisms, testability, request and response interception, typed request, and response objects. The HttpClientAPI rests on the XMLHttpRequest interface exposed by the browsers.

34. How does the Angular router work?

Answer: Angular router interprets a browser URL as commands to navigate to a client-generated view. Also, the router is bound to the links on a page. This way, Angular knows to navigate the application view to the required page when a user clicks on it.

35. What are the router navigation events?

Answer: Router navigation events help track the lifecycle of a route. These are:

• NavigationStart,
• RouteConfigLoadStart,
• RouteConfigLoadEnd,
• RoutesRecognized,
• GuardsCheckStart,
• ChildActivationStart,
• ActivationStart,
• GuardsCheckEnd,
• ResolveStart,
• ResolveEnd,
• ActivationEnd,
• ChildActivationEnd.
• NavigationEnd,
• NavigationCancel,
• NavigationError, and
• Scroll.

36. Is the routing module mandatory for an application?

Answer: No, the routing module can be totally skipped if there are simple configurations.

37. What is a wildcard route?

Answer: Wildcard route has a path that consists of two asterisks (**) that can match any URL. It is helpful when a URL doesn’t match any of the predefined routes. Instead of throwing errors, we can use a wildcard route and define a component for the same.

38. Explain the lifecycle hooks.

Answer: The set of processes that Angular goes through from initiation to end are collectively called lifecycle hooks. The following table explains the various lifecycle hooks in Angular:

39. How are animations done in Angular?

Answer: To use the animation module, we need to enable it. For this, the BrowserAnimationModule has to be imported. Example:

import { BrowserAnimationsModule } from '@angular/platform-browser/animations';
After this, import the required animation functions into the component files. Example,
import {
state,
animate,
transition,
// ...
} from '@angular/animations';

Next, add the animation metadata property within the @Component() decorator in the component file as shown below:

@Component({
selector: 'app-root',
templateUrl: 'app.component.html',
animations: [
// animation triggers go here
]
})

40. What are the special transition states?

Answer: Special transition states are wildcard (*) and void. Wildcard matches any animation state, while the void state configures transitions for elements entering or leaving a page.

41. How can you disable all the animations in Angular?

Answer: To disable all the animations, place the @.disabled host binding on the topmost Angular component.

42. Explain the steps to create a reusable animation.

Answer: To create an animation that can be reused, use the animation() method and define the animation in a separate .ts file. Declare this animation as a const export variable. This can then be imported and reused in any app components that use the useAnimation() API. Check an example on the Angular website .

43. Mention some of the functions that help control complex animation sequences.

Answer:

44. Explain the features of forms in Angular.

Answer: There are two approaches to handling form data (user inputs):

1. Reactive and
2. Template-driven.

Reactive forms are suitable when you are using reactive patterns in your application, and forms are a key part of your application. These forms are scalable, robust, and testable. We use template-driven forms to add simple forms. For example, a sign-up page. These are not as scalable as reactive forms and should be used only if your form requirements are simple and minimal.

Advanced-Level Angular Interview Questions

45. How will you represent metadata in Angular?

Answer: We can represent metadata using decorators like class decorators, property decorators, method decorators, and property decorators. Examples include @Component and @NgModule.

46. What are class decorators in Angular?

Answer: A class decorator contains the metadata of the suitable class type. It appears just before the class definition and declares the class to be of a certain type. Some class decorators are @Component, @NgModule, @Pipe, @Directive, and @Injectable.

47. Explain the difference between annotations and decorators in Angular.

Answer: Annotations are hardcoded features of Angular and store the array in them. The compiler creates an attribute of the annotated class and instantiates an object of the same name, passing the metadata to the constructor. Decorators, on the other hand, are functions that receive the object to be decorated. After receiving it, they are free to modify the object the way it likes. Moreover, the TypeScript compiler is responsible for implementing decorators.

48. What is the difference between class decorators and class field decorators?

Answer: Class decorators appear just before class definition, whereas class field decorators appear just before a field in the class definition. Examples of class decorators are @Component and @NgModule. @Input and @Output are examples of class field decorators.

49. What is package.json? Explain its purpose.

Answer: With the JSON package, it becomes easy to manage the project dependencies. We can mention details like the version, language, and so on, in package.json. For example, if TypeScript is used in our project, we can mention typescript and its version in package.json. Examples are metadata.json and tsconfig.json.

50. What does {{}} represent, and what is its use? Show an example.

Answer: The double curly braces represent interpolation, which is a special syntax. Angular converts it into property binding. You can think of it as an alternate for property binding. The name of the component is written inside the inner curly braces. During execution, the name is replaced by the actual string value of the property. For example:

<h2>
{{apptitle}}
<img src="{{imgname}}" style="height:30px">
</h2>

In the above code, Angular will evaluate and replace apptitle and imgname with their actual values.

51. What does the representation [()] mean?

Answer: This is a representation for NgModel used for two-way data binding. It is written as [(ngModel)] = “propertyvalue”.

52. What is a bootstrapping module in Angular?

Answer: A bootstrapping module is the root module that you bootstrap to launch the application. Every Angular application has a bootstrapping module. We can also refer to it as AppModule. The bootstrapping module is present in the AppModule class.

Code Example :

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

53. Talk about some differences between Promise and Observable.

Answer: The following table lists the differences between Promise and Observable:

54. What is a Single Page Application? How is it different from traditional web technology?

Answer: A single-page web application is a web page or website that rewrites the current web page dynamically with new content without reloading the entire web page. It is faster and easier to implement when compared with traditional web technology. In traditional technology, every time a user makes a request, the request is passed on to the server. This takes more time.

55. What are the different types of compilations in Angular?

Answer: Angular supports the following two types of compilations :

1. AOT (Ahead-of-Time) and
2. JIT (Just-in-Time).

56. List the differences between Just-in-Time (JIT) compilation and Ahead-of-Time (AOT) compilation.

Answer: With JIT, the compilation happens during the run time in the browser. It is the default option in Angular. The commands used for JIT compilation are:

ng build
ng serve

In AOT compilation , the compiler compiles the code during the build itself. The CLI commands for AOT compilation are:

ng build --aot
ng server –aot

AOT is more suitable for the production environment, whereas JIT is ideal for local development.

57. Which one is better out of AOT and JIT?

Answer: AOT reduces the load and boot time of the application. The pages also load faster. Any errors are also shown during the time of the application build itself. Hence, AOT is a better option.

58. Discuss some differences between Angular and jQuery. Which one is most suitable for a complex website with many workflows?

Answer: Here are the differences between Angular and jQuery :

Note : For a complex website with multiple workflows, Angular is more suitable as well as easier to develop and maintain.

59. What is an Angular library? Can you create your own library in Angular?

Answer: Angular library is a set of generic solutions that other developers have put together to be re-used. We can create our own library using Angular. In addition, we can publish and share these libraries as npm packages. However, we need to import an Angular library into the app.

60. What do you know about the npm package?

Answer: The components, framework, and CLI that the Angular applications use are packaged as npm packages. We can download Npm packages using the npm CLI client.

61. Write a sample code to create a library.

Answer: You can use the Angular CLI for this. The following set of commands generates a new library skeleton:

ng new my-workspace --create-application=false
cd my-workspace
ng generate library my-lib

Conclusion

If you want to learn Angular or AngularJS, check out some nice tutorials on YouTube, like this one: https://www.youtube.com/watch?v=k5E2AVpwsko

There are many other Angular interview questions and AngularJS interview questions, but this list covers all the basics and most frequently asked concepts.

Let us know in the comments if you want us to add more Angular interview questions from your personal experience to this list.

Thanks already.

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