50 Best Angular Interview Questions & Answers in 2021

50 Best Angular Interview Questions & Answers in 2021

This article will provide you with a list of the most commonly asked Angular interview questions and answers so that you can give the best answers.

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Let me guess, your JavaScript language knowledge has advanced to the point where you are interested in learning JavaScript frameworks. Well, you are not alone. As technology evolves, developers must learn about different frameworks that are in demand. By understanding the current frameworks, you improve your knowledge of the field and increase your odds of getting hired.

When it comes to JavaScript frameworks, Angular has proven to be an excellent platform for developing mobile and desktop applications. Therefore, the demand for Angular developers is quite high in the technical field. Hence, in the following article, we will look at some of the most frequently asked Angular interview questions you can expect during an Angular interview.

If you are a detail-oriented individual looking for an effective method to learn Angular, then the best angular tutorials can help you out.

Angular Interview Questions and Answers

This post presents some of the top Angular interview questions and answers you might expect during the interview. This list of questions also applies to Angular 6 interview questions and Angular 7 interview questions.

1. What is Angular?

Answer: TypeScript-based Angular is an open-source framework developed and maintained by Google for developing web applications. It offers an easy and powerful way of building front-end web-based applications.

Angular includes a range of features, including declarative templates, dependency injection, and end-to-end tooling that simplifies web application development.

2. What are some of the advantages of Angular over other frameworks?

Answer: Here are some advantages of Angular over other frameworks:

  • Declarative UI: Because HTML is a declarative language, Angular uses HTML to render the user interface of an application, making it easier to use than JavaScript.

  • Out of the box features: Angular comes with several built-in features such as routing, state management, rxjs library, and HTTP services. In other words, one does not need to search separately for the above-stated features.

  • Long-term Google Support: Google intends to continue working with Angular as it has offered long-term support for the framework.

3. Please explain the various features of Angular.

Answer: With its many features, Angular is an ideal framework for front-end JavaScript development. Here is a list of the most important factors:

  • Accessibility Applications: It supports the creation of accessible applications using ARIA-enabled components, an a11y test infrastructure, and developer guides.

  • Angular CLI: Angular supports command-line tools. You can use these tools to add components, test, and deploy instantly.

  • Animation Support: With Angular's intuitive API, you can create high-performance, complex animation timelines without writing extensive code.

  • Code Generation: Modern JavaScript virtual machines can use Angular to convert templates into highly optimized code.

  • Code Splitting: Angular apps load faster with the Component Router. By using the Component Router, the code gets automatically split so that only the code needed to render the view requested by the user is loaded.

  • Cross-Platform App Development: Developers can use Angular to build desktop, native, and progressive web apps. Cordova, Ionic, and NativeScript are all supported by Angular for building native mobile applications. Modern web platforms allow creating high-performance, zero-step installation, and offline progressive web apps using Angular. Additionally, developers can build desktop apps with Angular for Linux, macOS, and Windows.

  • Synergy with Popular Code Editors and IDEs: You can use Angular with most source code editors and IDEs since it offers code completion, instant errors, etc.

  • Templates: It lets you create UI views in a simple and powerful template syntax.

  • Testing: Karma allows you to run frequent unit tests in Angular. Faster scenario tests can be run with the Protractor.

4. Why was Angular introduced as a client-side framework?

Answer: Developers traditionally used VanillaJS and jQuery to create dynamic websites. As websites became more complex with additional features and functionality, developers found it increasingly difficult to maintain the code. Furthermore, jQuery did not provide data handling capabilities across views. Therefore, Angular was built to address these issues, making development easier for developers by dividing code into smaller pieces of information called Components in Angular.

With client-side frameworks, advanced web applications like SPAs are developed more quickly than if developed by VanillaJS.

5. Define the ng-content Directive?

Answer: Conventional HTML elements contain some content in between the tags. For example:

<p>Put your paragraph here</p>

Take this example of customized text between angular tags as an example:

<app-work>This won’t work like HTML until you use ng-content Directive</app-work>

However, doing so won't work as it did for HTML elements. To make it work as per our HTML example, we will need to use the ng-content directive. Additionally, it facilitates the creation of reusable components.

6. What is an AOT compilation? What are the advantages of AOT?

Answer: Each Angular application contains components and templates that are unreadable by the browser. As a result, all Angular applications should be compiled first before being run in a web browser.

Angular offers two types of compilation:

  • JIT(Just-in-Time) compilation
  • AOT(Ahead-of-Time) compilation

Advantages:

  • By compiling the application before it runs inside the browser, the browser loads the executable code and renders the application immediately, which results in faster rendering.
  • Errors can be detected and handled during the building phase, which minimizes errors.
  • Before JS files run in the browser, the AOT compiler adds HTML and templates to them. As a result, it eliminates the need to read additional HTML files, thus enhancing the application's security.
  • With AOT compilation, the compiler sends the external HTML and CSS files along with the application, eliminating separate AJAX requests for those files, which results in fewer AJAX requests.

7. List out differences between Angular and AngularJS.

Answer: Here are the differences between Angular and AngularJS:

Architecture:

  • MVC or Model-View-Controller architecture is used in AngularJS, where the Model contains the business logic, the Controller processes data, and the View displays the information in the Model.

  • Angular uses components instead of controllers. Components are nothing more than directives with predefined templates.

Language:

  • AngularJS uses JavaScript, a dynamically typed language.
  • Angular uses TypeScript, a statically typed language based on JavaScript. While developing larger applications, Angular provides better performance due to its statically typed language.

Mobile Support:

  • Mobile support is not available in AngularJS.
  • All popular mobile browsers support Angular.

Structure:

  • In the case of AngularJS, maintaining code becomes tedious when developing larger applications.
  • Because Angular provides a better structure, it is easier to maintain code for larger applications.

Expression Syntax:

  • A developer must remember the correct ng-directive for binding an event or a property when creating an AngularJS application.
  • While in Angular, property binding is done using the "[ ]" attribute, and event binding is done using the "( )" attribute.

8. What are some disadvantages of using Angular?

Answer: While Angular offers quite a few benefits, it also has some disadvantages. Here they are:

  • An Angular application can be difficult to optimize for SEO and may require some configuration to get good results.
  • It can be difficult to get to know all the features in Angular and how to use them together effectively.
  • Since Angular can add a significant amount of weight to a JavaScript bundle, using it for small projects is very inefficient and can significantly increase loading time.

9. What do you mean by data binding?

Answer: Data binding is one of the most important and powerful features that help establish communication between DOM and components. It simplifies the creation of interactive applications because you no longer have to worry about data pushing or pulling between the component and the template.

Angular has four different ways of binding data:

  • Event binding
  • Property binding
  • String interpolation
  • Two-way data binding

10. What are some advantages of using Angular?

Answer: There are several advantages to using Angular, which are listed below:

  • Angular is built using TypeScript, which lets developers write strongly-typed code that will get translated into JavaScript. Having strongly-typed code means it is easy to read, maintainable, and less likely to contain errors. Additionally, it offers better code completion and type hints.
  • You can use the modules in Angular to wrap specific functionalities, such as HTTP communication, data validation, routing, etc.
  • Angular has a large ecosystem of tools, libraries, frameworks, plugins that make the development process faster and more enjoyable. Angular CLI, RxJS, NgRx, etc., are among these tools and libraries.

11. What are the technologies used in Angular?

Answer: Google developed Angular, a modern JavaScript framework for front-end development. To accomplish certain tasks easily and to allow developers to have a better experience while developing applications, Angular uses several technologies. TypeScript is a superscript of JavaScript, which Angular uses. Therefore, any valid JavaScript is also a valid TypeScript. In addition to being a tight-typed language, TypeScript lets us define types, making catching bugs much easier. Developers can also deal with asynchronous operations better using RxJS.

12. What do you mean by string interpolation?

Answer: String interpolation in Angular, also called the mustache syntax, allows only one-way data binding. To display the component data, it makes use of double curly braces [[]]. The braces contain the JavaScript expressions that Angular needs to execute to retrieve the result, which later gets inserted into HTML. Furthermore, these expressions are regularly updated and stored as part of the digest cycle.

13. What are the components in Angular?

Answer: In Angular, components form the basis of the user interface. Each component of a user interface is composed of HTML, CSS, and JavaScript. You can think of these as HTML elements that only Angular can understand. Due to namespacing, these components are all isolated from each other. The styles and code of one component will not affect the styles and code of another component. By assembling these components, Angular builds the user interface for the browser.

14. What is DOM?

Answer: DOM is a document object model used to represent the content of a web page and changes to an application's architecture. A tree-like object structure organizes all the objects, and the document can be easily modified, manipulated, and accessed only with APIs.

15. What are modules in Angular?

Answer: Modules define logical boundaries within our application. These are used to encapsulate code that deals with a specific aspect of the application, for example, routing, HTTP, validation, etc. Modules are used to make applications more composable. For example, if we wish to implement validation logic using a different library, then for the application we have already implemented, we can create a new validation module and replace the one we currently have with the new one, and our application will still function properly. By using NgModule decorator, we create modules in Angular.

16. What are services in Angular?

Answer: In Angular, services cover a wide range of functionality. Any value, function, or feature that an app requires is a service. Services are typically used for narrow purposes such as HTTP communication, sending data to a cloud service, decoding some text, validating data, etc. Services specialize in one thing and do it well. It is different from a component in that it does not concern itself with HTML or any other type of presentation logic. Multi-tasking is normally accomplished by a component using several services.

17. What are templates?

Answer: An Angular template is written in HTML that includes elements and attributes specific to Angular. Furthermore, the templates are combined with data from the controller and the model, which can be rendered to offer the user a dynamic view.

18. What are pipes in Angular?

Answer: It is sometimes necessary to manipulate or transform data before putting it into our templates to output some dynamic data. While there are several ways to accomplish that in Angular, pipes are the most preferred method. Pipes are just simple functions that we can use with expressions in our templates.

After declaring them once and registering them with the Angular framework, we can use pipes throughout our application. The most common built-in pipes in Angular are UpperCasePipe, LowerCasePipe, CurrencyPipe, etc.

19. What is the difference between jQuery and Angular?

Answer: Angular is a JS front-end framework, whereas jQuery is a JS library. Below are some other differences between the two:

  • In contrast to jQuery, Angular offers two-way data binding.
  • jQuery does not offer support for RESTful APIs like Angular.
  • jQuery does not support deep linking routing while Angular does.
  • Angular supports form validation, but jQuery does not.

Even though Angular and jQuery have their differences, they also have some similarities, such as both jQuery and Angular expressions consist of variables, operators, and literals.

20. What is a two-way data binding?

Answer: Angular uses two-way data binding to ensure that the data model and view are automatically synchronized. For example, if some data is updated in a model and that model is displayed in multiple places in a component, that data update should be reflected in all of those places.

Angular has supported two-way data binding for a long time. It is, however, something that should be used with caution as it could result in poor application performance or performance degradation over time. In two-way data binding, we can change some data in the component model from the HTML view, and that change is propagated to all other places in the HTML view where it is displayed.

21. What are lifecycle hooks in Angular?

Answer: In Angular apps, we may need to execute some code at specific events - such as when a component is being initialized, displayed on the screen, or removed from the screen. Lifecycle hooks are used for this purpose. For example, if we have some event listeners attached to the HTML elements in a component, like a button click or form submission, we can remove these before removing the component from the screen. We can also fetch some data and display it in a component after the component has loaded. We can override some component methods, such as ngOnInit or ngAfterViewInit, to use a lifecycle hook. Angular will call these methods automatically if they are available on a component. That is why they are called lifecycle hooks.

22. What does Angular Material mean?

Answer: A UI component library, Angular Material enables professionals to build web applications and websites that are consistent, attractive, and fully functional. To do this, it must follow modern principles of web design, such as graceful degradation and browser probability.

23. How are observables different from promises?

Answer: Both promises and observables are used to handle asynchronous requests in JavaScript, but they operate differently. While promises can handle only one event at a time, observables can handle a sequence of asynchronous events over time. Furthermore, observables provide us with a variety of operators that allow us to transform data flowing through them with ease.

A promise just wraps asynchronous operations so that they can be easily reused, while an observable's purpose is to construct a stream of data for delivery to a subscriber via a well-defined path, where multiple operations transform the data along the way.

24. What is RxJS?

Answer: RxJS is a library that stands for Reactive Extensions for JavaScript. The intent is to allow us to use observables in our JavaScript projects, which enables reactive programming. In many popular frameworks such as Angular, RxJS is used to combine asynchronous operations or callback-based code into a series of operations that emit values from a publisher to a subscriber. Additionally, other languages such as Java, Python, etc. have libraries that allow them to write reactive code by using observables.

25. What do you mean by dependency injection?

Answer: Dependency injection (DI) in Angular is a software design pattern that allows objects to be passed as dependencies rather than having to hard-code them in the respective components. This concept is extremely useful when it comes to separating the creation of object logic from its consumption.

The "config" function uses DI that must be configured to enable the module to retrieve the application elements. Furthermore, this feature allows professionals to change dependencies according to their needs.

26. What is bootstrapping?

Answer: In simple terms, Angular bootstrapping allows professionals to start the Angular application. Both manual and automatic bootstrapping are supported by Angular. Let's briefly compare the two.

  • Automatic Bootstrapping: In the case of professionals who need Angular to automatically bootstrap their application, automatic bootstrapping can be used to add the ng-app directive to the application's root, often on the tag. Once Angular finds the ng-app directive, it loads the associated module and compiles the DOM.

  • Manual Bootstrapping: By using manual bootstrapping, professionals have more control over how and when to initialize the Angular app. The tool is very useful in places where professionals wish to perform other tasks and operations before the Angular compiles the page.

27. What is the digest cycle process in Angular?

Answer: The digest cycle in Angular tracks changes in the watch variable value by monitoring the watchlist. Each digest cycle compares the current and previous versions of the scope model values.

28. What are the distinct types of Angular filters?

Answer: Filters in Angular provide formatting for expression values to be displayed to the user. A directive, template, or controller can contain them. Additionally, you can create customized filters according to your needs. You can use these filters to organize the data so that only the data that match your criteria will be displayed. When used in expressions, filters are placed after the pipe symbol ( | ).

Below are some types of filters in Angular:

  • currency: It converts numbers to the currency format
  • filter: It selects a subset containing items from the given array
  • date: It converts a date into a necessary format
  • lowercase: It converts the given string into lowercase
  • uppercase: It converts the given string into uppercase
  • orderBy: It arranges an array by the given expression
  • json: It formats any object into a JSON string
  • number: It converts a number value into a string
  • limitTo: It limits the number of characters that can be in an array or string.

29. How can one create a service in Angular?

Answer: In Angular, a service is an object that can be substituted. With the help of dependency injection, it is wired and combined. To develop services, they need to be registered in the module that will execute them. Angular provides three ways to create a service:

  • Factory
  • Provider
  • Service

30. Describe Angular authentication and authorization.

Answer: On a server, an authentication API receives the login details of a user. The server validates the credentials and returns a JSON web token (JWT), which includes attributes and the data of the current user. Furthermore, the user is easily identified by using JWT, and this is known as authentication.

Upon logging in, users have various types and levels of access-some have unlimited access, while others have restrictions. These users' access levels are determined by their authorization.

31. Explain the MVVM architecture.

Answer: MVVM architecture significantly reduces tight coupling between components. There are three parts to this architecture:

  • Model: The data and logic of an application are represented by the model. It consists of an entity structure. The model has the business logic, along with model classes, remote and local data sources, and the repository.
  • View: This is the visual layer of the application that is comprised of the UI code. ViewModel receives the user's action from the view. It does not receive the response directly, however. For the view to receive a response, it must subscribe to the observables exposed by the ViewModel.

ViewModel: The application's abstract layer connects the View and the Model, acting as a bridge between them. Since it doesn't have direct access to the View, it doesn't know which View needs to be used. Data binding connects the two, and the ViewModel records all the changes made to the View and updates the Model accordingly.

32. Could we make an angular application to render on the server-side?

Answer: Angular Universal, a technology provided by Angular, allows applications to be rendered on the server-side. Angular Universal offers the following benefits:

  • Better User Experience: Instantly shows users the view of the application.
  • Better SEO: Universal content is accessible on every search engine, resulting in better SEO.
  • Loads Faster: Because render pages are available to browsers sooner, server-side applications load faster.

33. Demonstrate navigating between different routes in an Angular application.

Answer: The following is a snippet of code that shows how to navigate between different routes in an Angular application named "Some Search App":

import from "@angular/router";
.
.
.
@Component({
  selector: 'app-header',
  template: `
<nav class="navbar navbar-light bg-faded">
  <a class="navbar-brand" (click)="goHome()">Some Search App</a> 
  <ul class="nav navbar-nav">
    <li class="nav-item">
      <a class="nav-link" (click)="goHome()">Home</a> 
    </li>
    <li class="nav-item">
      <a class="nav-link" (click)="goSearch()">Search</a> 
    </li>
  </ul>
</nav>
 `
})
class HeaderComponent {
  constructor(private router: Router) {} 
  goHome() {
    this.router.navigate(['']); 
  }
  goSearch() {
    this.router.navigate(['search']); 
  }
}

34. Enumerate some salient features of Angular 7.

Answer: The 7th major release of Angular has been split into @angular/core, unlike previous versions. The purpose of this is to reduce the size of the file. An Angular developer typically does not need every module. Therefore, each split of @angular/core in Angular 7 will have no more than 418 modules.

Additionally, Angular 7 supports drag-and-drop and virtual scrolling. The latter enables the loading and unloading of DOM elements. Virtual scrolling is available with the latest version of Angular. Furthermore, Angular 7 is integrated with a new and enhanced ng-compiler.

35. What does subscribing mean in RxJS?

Answer: In RxJS, when using observables, we must subscribe to the observable to make use of the data that flows through it. Data is generated by a publisher and consumed by a subscriber. To subscribe to an observable, we pass in a function for the data and another function for errors, so that if there are any errors, we can send some message or process the message.

36. What is the scope?

Answer: Within Angular, scope refers to an application model. The context is used to execute expressions. Similar to the DOM structure of the application, these scopes are organized hierarchically. Scopes help propagate events and watch expressions.

37. What is REST?

Answer: Angular's REST stands for Representational State Transfer. It is an API that works with HTTP requests. In this case, the requested URL points to the data that must be processed, after which an HTTP function is used to determine the operation that should be performed on the data. The APIs that follow this method is known as RESTful APIs.

38. Explain Angular CLI.

Answer: Angular CLI is also known as the Angular command-line interface. Professionals can use these CLI tools to add components, deploy them instantly, and perform testing, and many other functions.

39. What is the role of SPA in Angular?

Answer: SPA stands for Single Page Application. Even when the URL changes constantly, this technology only keeps one page, index.HTML. Compared to traditional web technology, SPA technology is easy to build and extremely fast.

40. What is Angular Router?

Answer: With a single-page frontend application, routing involves responding to changes in URLs that are made by adding and removing content. Since we do not want the browser to reload, we need to intercept a request that changes the browser's URL. Then, we must decide which content should be removed and which should be added, and, finally, the URL of the browser must be changed too to show the user the current page.

We can see that this is very difficult to implement, especially in multiple applications. Because of this, Angular provides a full routing solution. Angular handles route processing using these routes with matching components.

41. What is HttpClient, and what are its benefits?

Answer: The HTTPClient Angular module is used to communicate with a backend service using the HTTP protocol. For sending requests in frontend applications, we usually use the fetch API. The fetch API, however, uses promises. While promises are useful, they are not as flexible as observables. Because of this, HttpClient is used in Angular, since it returns data as an observable, which we can subscribe to, unsubscribe from, and do various operations on. Moreover, you can create an observable from a promise, or you can convert observables to promises.

42. What is the PipeTransform interface?

Answer: Its name implies receiving an input value and transforming it into the desired format using the transform() method. Typically, it is used to implement custom pipes.

import { Pipe, PipeTransform } from '@angular/core';

 @Pipe({

  name: 'demopipe'

})

export class DemopipePipe implements PipeTransform {

  transform(value: unknown, ...args: unknown[]): unknown {

    return null;

  }



}

43. What is multicasting in Angular?

Answer: Angular allows us to broadcast data to multiple subscribers in one execution when we use the HttpClient to communicate with a backend service and retrieve some data. Multicasting is the process of sending data to multiple subscribers. In particular, we can use it when more than one element of our application is waiting on data. We need an RxJS subject to use multicasting. Since observables are unicast, they do not allow multiple subscribers. Subjects, however, allow multiple subscribers and are multicast.

44. How to generate a class in Angular 7 using CLI?

Answer:

ng generate class Dummy [options]

This will create a class named Dummy.

45. What is Eager and Lazy loading?

Answer: The default module loading strategy is eager loading. Applications with Eager loading load feature modules before they launch. It is typically used for small applications.

Dynamically loading feature modules on demand is called lazy loading. The application becomes faster as a result. In large applications, where all the modules are not required at the beginning, this method is used.

46. Explain the difference between an Annotation and a Decorator in Angular?

Answer: In Angular, annotations are used to create an annotation array. There is only one metadata set for each class using the Reflect Metadata library.

Decorators in Angular are used to separate decoration or modification of a class without changing its source code.

47. What is ngOnInit()? How to define it?

Answer: Angular calls ngOnInit() after all the data-bound properties of a directive has been initialized. It can be defined as:

Interface OnInit {
 ngOnInit() : void
 }

48. What are directives in Angular?

Answer: One of the core features of Angular is directives. Angular developers can use them to create application-specific HTML syntax. In reality, directives are functions that are executed by the Angular compiler when it finds them in the DOM. There are three types of directives:

  • Attribute Directives
  • Component Directives
  • Structural Directives

49. Why prioritize TypeScript over JavaScript in Angular?

Answer: As a superset of Javascript, TypeScript includes features like typecasting for variables, annotations, variable scope, and more. Javascript's shortcomings are overcome by using typescript, like typecasting of variables, classes, decorators, variable scope, and others. Furthermore, Typescript is purely object-oriented programming that offers a "Compiler" to produce Javascript-equivalent code.

50. What is the difference between AOT and JIT?

Answer: Ahead of Time: Compiling your code ahead of time (AOT) occurs during the build process before the browser downloads it. In this way, the browser receives faster rendering. If you wish to specify AOT compilation when you run ng build or ng serve, simply add the --aot option to the command.

During runtime or execution, Just-in-Time (JIT) compilation compiles computer code to machine code. It is also called dynamic compilation. When you run the ng build or ng serve CLI commands, JIT compilation is the default.


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