Top 40 Angular interview questions and answers

Safalta Expert Published by: Aryan Rana Updated Thu, 15 Sep 2022 12:19 AM IST

Highlights

Angular is a powerful front-end JavaScript framework that is frequently utilised in the creation of apps. There is a huge need for Angular developers as a result of its growing popularity. Some frequently requested questions and solutions are provided in this post on Angular Interview Questions. There are two levels of questions: beginner and advanced.

The popular front-end JavaScript framework Angular is used to build apps. There is a huge need for Angular developers as a result of its rising popularity. In this article on Angular Interview Questions, we'll go through some often requested questions and how to respond to them. The questions are divided into two categories: beginner and advanced. 

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Angular Interview Questions And Answers


1. Describe Angular. How it was introduced?


Single Page Applications were the reason Angular was developed. This framework offers exceptional scalability and maintainability as well as structure and consistency to online applications.

An open-source JavaScript framework called Angular was entirely written in TypeScript.

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It expresses the components of your programme using the syntax of HTML.
 

2. What is TypeScript?


A superset of JavaScript called TypeScript provides outstanding consistency. It comes highly recommended because it adds some syntactic sugar and makes the code base easier to comprehend and manage. Ultimately, TypeScript code is reduced to JavaScript, which can operate effectively in any setting.
 

3. How does data binding work? Angular uses what kind of data binding?


The phenomenon of data binding makes it possible for any internet user to edit elements of a Web page using a web browser. No complicated coding or programming is needed because it uses dynamic HTML. In web pages with interactive elements like tutorials, games, calculators, and forms, data binding is used. Data binding is convenient when pages include a lot of data because of the incremental presentation of a webpage.

In Angular, two-way binding is used. The matching model state reflects any alterations made to the user interface. On the other hand, any modifications to the model state are also reflected in the UI state. This enables the framework to use the controller to link the DOM to the Model data. However, because every DOM modification must be recorded, this strategy has an impact on performance.
 

4. What are Single Page Applications (SPA)?


Web apps known as single-page applications only load once and only add new functionality to the user interface. The content of the new page is produced dynamically rather than loading new HTML pages. JavaScript's ability to work with the DOM elements on the current page itself makes this possible. A SPA method offers a seamless user experience because it is quicker.
 

5. Explain the differences between Angular and AngularJS.


The detailed comparison between Angular and AngularJS is shown in the table below:
 

Feature

AngularJS 

Angular

Language

JavaScript

TypeScript

Architecture

Supports Model-View-Controller design

Uses components and directives

Mobile support

Not supported by mobile browsers

Supports all popular mobile browsers

Dependency Injection

Doesn’t support 

Supports

Routing

@routeProvider is used to provide routing information

@Route configuration is used to define routing information

Management

Difficult to manage with an increase in source code size

Better structured, easy to create and manage bigger applications

 

6. What are Angular decorators?


A design pattern or set of functions called decorators defines how Angular features operate. They are employed to carry out earlier adjustments to a class, service, or filter. There are four categories of decorators that Angular supports:

  • Decorative students
  • Interior Decorators
  • Decorators of both parameters and methods


7. List a few of Angular's advantages.


The following are some of the benefits of using Angular:
  • MVC architecture: Angular is an MVC framework in its entirety. It offers a strong judgement on the best way to organise the application. Additionally, it updates the real DOM and provides bi-directional data flow.
  • Modules: Angular has a variety of design patterns, such as components, directives, pipelines, and services, to aid in the efficient development of applications.
  • Dependency injection: This feature makes it simple to get around components that depend on other components.
  • Other general benefits include unit testing, reusable components, data binding, clean and maintainable code, and outstanding responsiveness.


8. What new features does Angular 10 offer?

  • TypeScript 3.6, 3.7, and even 3.8 were supported by earlier versions of Angular, however, older versions are no longer supported. However, TypeScript was upgraded to TypeScript 3.9 with Angular 10.
  • CommonJS import warnings - Unknown property bindings or element names in templates are now logged at the "error" level instead of just at the "warning" level.
  • When you establish a new workspace with the ng new command in Version 10, a stricter project setup is available as an optional feature.

new —strict ng

NGCC Feature: NGCC features are added with the aid of a program-based entry point finder.
  • New URL routing
  • Deprecated APIs - There are a number of deprecated APIs in Angular 10.
  • Bug corrections - This release of Angular 10 includes a number of bug fixes, the most significant of which prevent the compiler from generating undefined expressions and the core from experiencing a migration error when importing a symbol that doesn't exist.
  • New Default Browser Setting - The default browser configuration has been updated to outperform outdated and infrequently used browsers.


9. What are Angular Templates?


HTML is used to create Angular Templates, and this HTML includes Angular-specific elements and properties. These templates are further generated in conjunction with the data from the model and controller to give the user a dynamic view.
 

10. What are Angular annotations?


In Angular, an annotation array is made using annotations. They are the metadata that has been set on the class to represent the metadata library.
 

11. What are Angular directives?


By using directives, users can create new HTML syntax that is tailored to their applications. When the Angular compiler locates them in the DOM, they are executed. The three sorts of directives that Angular provides.
  • Participant Directives
  • Architectural Instructions
  • Object Directives


12. what is An AOT compilation? What benefits does it offer?


AOT compilations: What are they? Which advantages does it have?

During the build step, or before the browser downloads and runs the code, the Ahead-of-Time (AOT) compiler transforms the Angular HTML and TypeScript code into JavaScript code.

Listed below are a few of its benefits.
  • More rapid rendering
  • Fewer asynchronous requests
  • The download size for the Angular framework is less.
  • Errors in templates are quickly found
  • Improved safety


13. What are Angular components?


An Angular application's user interface is composed primarily of components. Every component has a template assigned to it, and each component is a subset of the directives. The AppComponent acts as the root component in an Angular application and branches out into other components to form a hierarchy.
 

14. What are Angular Pipes?


Pipes are straightforward functions that, in a more technical sense, take an input value, process it, and then return the altered value as an output. Numerous pipelines are supported by Angular. Custom pipes, on the other hand, can be made to your specifications.

Among the essential elements are:
  • The pipe sign, "|," is used to define pipes.
  • It is possible to chain pipes together.
  • The colon (:) symbol can be used to pass parameters to pipes.


15. What does the interface PipeTransform do?


According to its name, the interface uses the transform() method to change an input value into the appropriate format. Custom pipelines are frequently implemented using it.

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

 @Pipe({

  name: 'demopipe'

})

export class DemopipePipe implements PipeTransform {

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

    return null;

  }

 

}
 

16. What are Pure Pipes?


These pipes are those that employ only pure functions. Because of this, a pure pipe doesn't employ any internal state; instead, the output stays constant so long as the parameters given do not change. The pipe is only called by Angular when it notices a change in the arguments being given. The pure pipe is implemented in all components as a single instance.
 

17. How do Impure Pipes work?


Regardless of changes to the input fields, Angular calls an impure pipe for each cycle of change detection. For these pipes, several pipe instances are produced. These pipes can receive changeable inputs.

All pipes are initially pure. However, as illustrated below, you can define impure pipes by utilising pure property.

@Pipe({

  name: 'demopipe',

  pure : true/false 

})

export class DemopipePipe implements PipeTransform {
 

18. Describe a ngModule.


A block of code is reserved for an application domain or a workflow by NgModules, which are containers. To compile a component's template and create an injector at runtime, @NgModule accepts a metadata object that typically explains these processes. Additionally, it uses the export property to identify the module's parts, directives, and pipes, some of which are made public for usage by external components.
 


19. What do filters in Angular mean? List a few of them.


An expression is shown to the user in a formatted form thanks to filters. View templates, controllers, and services can all make use of them. Here are a few built-in filters.

date – Format a date according to a predefined format.
Choose a portion of an array's items with the filter command.
JSON – Convert an object to a JSON string.
limitTo - Reduces an array or string to a predetermined number of components.
lowercase - Lowercase a string's formatting.
 

20. What does Angular's view encapsulation mean?


If the template and styles defined within the component can impact the entire application or not depends on the view encapsulation. There are three encapsulation methods offered by Angular:
  • Emulated – the component receives styling from the main HTML.
  • Native - the component does not inherit styles from the main HTML.
  • None; all components on the page can see the styles because they propagate from the component back to the main HTML.


21. How do controllers work?


The data in AngularJS apps are managed via AngularJS controllers. Normal JavaScript Objects are what they are. The application controller is specified by the ng-controller directive.
 

22. What does "scope" in the context of Angular mean?


The HTML, or view, and the JavaScript, or controller, are connected by the scope in Angular. It is an object with the available methods and properties, as would be expected. Both the view and the controller have access to the scope. The $scope object is passed as a parameter when creating a controller in Angular.
 

23. Describe the Angular lifecycle hooks.


Every component in Angular has a lifecycle. These components are created, rendered, and destroyed by Angular before being eliminated from the DOM. The use of lifecycle hooks allows for this. The list of them is as follows:
  • When Angular sets or resets data-bound input properties, ngOnChanges() reacts.
  • Initialize the directive or component using ngOnInit() after Angular shows the data-bound attributes and sets the input properties for the directive or component./
  • ngDoCheck() - Find and handle changes that Angular is unable or unwilling to find on its own.
  • After Angular renders external content into the component's view, the ngAfterContentInit() function reacts.
  • Respond using ngAfterContentChecked() after Angular has examined the content that was projected into the component.
  • Respond using ngAfterViewInit() once Angular has initialised the component's views and child views.
  • Respond following Angular's inspection of the component's views and child views with ngAfterViewChecked().
  • Prior to Angular destroying the directive or component, ngOnDestroy allows cleanup.


24. What does Angular's String Interpolation do?


A one-way data-binding method called string interpolation outputs data from TypeScript code to an HTML page. Using two curly braces is indicated. The data from the component is displayed in the view with the aid of this template expression.

{{ data }}
 

25. How do template statements work?


HTML uses template declarations as methods or attributes to react to user events. With the help of these template statements, the application you develop or are working on will be able to engage users by presenting dynamic content and allowing them to submit forms.

For instance,

Button with "deleteHero()" clickable.

Delete button "hero"

This page's template is deleteHero. The user clicking the button causes the method to be invoked.
 

26. What distinguishes AOT and JIT from one another?


Prior to the browser downloading and running your code, AOT compilation converts your code during the development process. This guarantees quicker browser rendering. Include the —aot option with the ng builds or ng serve command to specify AOT compilation.

During execution, or run time, computer code can be converted to machine code using the Just-in-Time (JIT) compilation process. Additionally called dynamic compilation. When you use the CLI commands ng build or ng serve, JIT compilation is used by default.
 

27. Describe the @Component Decorator.


Components can be created using a TypeScript class. The "@Component" decorator is then applied to this class's genre. The decorator's function is to take a metadata object that contains pertinent details about the component and accept it.
 

28. What do the Angular Services mean?


Multiple components use Angular Services to complete tasks. These duties might include database maintenance, network connectivity, and data and picture retrieval. They carry out all of the operational duties for the parts without having to rewrite any code. It is possible to create a service once and inject it into all the components that use it.
 

29. What do Angular's promises and observables mean?


Whereas both concepts in Angular deal with asynchronous events, observables deal with a series of events over a period of time while promises deal with a single event at a time.

Promises: They only ever emit a single value. They don't allow for cancellation and start working right away after creation. To the child's promises, they are Push mistakes.

Observables: Only when the subscribe() method is used to subscribe to them are they actually executed. Over time, they emit a variety of values. They support a variety of activities, including forEach, filter, and retry. They provide subscribers with errors. The listener stops receiving new values when the unsubscribe() method is used.
 

30. Describe ngOnInit. What does it mean?


Angular uses the callback method and lifecycle hook ngOnInit to signal the creation of a component. It returns a void type and accepts no parameters.

export class MyComponent implements OnInit {

  constructor() { }

  ngOnInit(): void {

    //....

  }

}
 

31. How can ngFor be used in a tag?


In the HTML templates, lists and tables are created using the ngFor directive. Simply put, this directive is used to construct a template for each element in an array or object by iterating through them.
 
  •  

         
  • {{ item }}



  •  
  •    
  • A local variable is created by "let item" and is accessible in the template.
  • The phrase "of items" denotes that we are repeating the list of iterable things.
  • A parent template is created by the * before ngFor.


32. What are Reactive forms and Template forms?


Template-driven approach
  • The standard form tag is utilised in this manner to generate forms. The tag is automatically interpreted by Angular, which also generates a form object representation.
  • The NGModel tag can be used to add controls to a form. The NGControlGroup module can be used to group several controls.
  • The "form. value" object can be used to create a form value. When the submit method is called, form data is exported as JSON values.
  • The form fields can be verified using fundamental HTML validations. The usage of directives is possible in the event of unique validations.
  • This technique might be said to be the simplest for developing Angular apps.

Response-Focused Approach
  • This method is the programming paradigm that is focused on data flows and the spread of change.
  • Data flows between form controls and data models are directly managed by the component when using reactive forms.
  • Unlike a template-driven technique, reactive forms are driven by code.
  • Reactive forms depart from the standard declarative methodology.
  • Reactive forms do away with the anti-pattern of using two-way data binding to update the data model.
  • Synchronous programming approaches can be used to unit test Reactive form control creation, which is typically synchronous.


33. Describe Bootstrap. How does Angular integrate it?


A strong toolset is Bootstrap. Developing responsive web pages and online applications is a set of HTML, CSS, and JavaScript tools.

The bootstrap library can be integrated into your programme in two different methods.
  1. CDN-based Angular Bootstrap - Bootstrap Public content delivery networks are known as CDNs. It allows you to remotely access its servers and load the CSS and JavaScript files.
  2. Installing Bootstrap into your project folder using NPM is another option to include it in your Angular project (Node Package Manager).

install bootstrap using npm

install jquery using npm
 

34. What are Eager and Lazy loading refer to?


The standard module-loading approach is eager loading. Before the application launches, feature modules with Eager loading are loaded. This is frequently applied to small-scale projects.

When there is a need, dynamic lazy loading loads the feature modules. This speeds up the application. When using larger programmes, it is employed when not all modules are needed right away.
 

35. What DOM implementation does Angular use?


An XML or HTML document is treated by the document object model (DOM) as a tree structure in which each node is an object that represents a section of the content.

Regular DOM is used by Angular. Up until the updated data is reached, the complete HTML tag tree is updated. But Angular uses Change Detection to make sure that speed and performance remain unaffected.

You have now reached the article's conclusion. For an interview, we strongly advise brushing up on the fundamental ideas. Writing the code where it is required is usually beneficial.
 

36. Why were Angular and other client-side frameworks developed?


A more responsive user experience was made possible with the introduction of client-side frameworks like Angular. A framework allows programmers to make web apps that are more interactive and hence offer a better user experience.

Single-page applications can also be more easily made by developers thanks to frameworks like Angular (SPAs). Web applications known as SPAs only require one HTML page to load. Compared to conventional web apps, they are consequently significantly faster and more responsive.

In order to enhance the user experience of online applications, client-side frameworks like Angular were launched. They improve the experience for both developers and users by making web apps more responsive and simpler to develop.
 

37. What is the operation of Angular applications?


Single Page Applications, or SPAs, are what make up an Angular application. This implies that the entire programme is contained within a single page and that all resources (such as HTML, CSS, JavaScript, etc.) are loaded at page load time. Model-View-Controller or MVC, architecture paradigm is used by Angular to manage its data and views. The data that the application utilises is the Model, the user sees the View, and the Controller is in charge of coordinating communication between the Model and the View.

An Angular application's view will be updated automatically by the Angular framework whenever a user interacts with it. As a result, Angular applications are extremely responsive and quick because users don't have to wait for the page to reload in order to see new information.

Due to their ability to be broken up into individual modules that can be loaded independently of one another, Angular apps can be scaled up relatively easily. This implies that Angular applications can simply be expanded with additional functionality without needing to be completely rewritten.

Applications built with Angular are often quick, responsive, and scalable. They offer a fantastic user experience and are simple to design and expand.

An example of code from an angular.json file is as follows:

 "build": {

        "builder": "@angular-devkit/build-angular:browser",

        "options": {

          "outputPath": "dist/angular-starter",

          "index": "src/index.html",

          "main": "src/main.ts",

          "polyfills": "src/polyfills.ts",

          "tsConfig": "tsconfig.app.json",

          "aot": false,

          "assets": [

            "src/favicon.ico",

            "src/assets"

          ],

          "styles": [

            "./node_modules/@angular/material/prebuilt-themes/deeppurple-amber.css",

            "src/style.css"

          ]

        }

      }
 

 

38. For its apps, Angular by default use client-side rendering.


This indicates that the user's web browser is where the Angular application is rendered on the client side. The performance and security of client-side rendering are two of its many benefits. However, using client-side rendering has significant disadvantages as well. One of the greatest disadvantages is that it could make it harder to debug your programme.

Client-side rendering is generally employed in less data-driven applications. Client-side rendering might be exceedingly slow if your application uses a lot of data from a server. Additionally, it's crucial to be careful with how you load and cache your data if you're using client-side rendering. If you're not careful, you may wind up with an extremely sluggish and challenging application. This is referred to as Angular Universal when rendered on the server side.
 

39. How does Angular handle data sharing between components?


In Angular, data sharing between components is basic and straightforward. All you have to do to share data is create a new service using the Angular CLI. Any component can have this service injected into it, enabling data sharing between components.

Use the Angular CLI command below to create a new service:

service generated by ng my-data-service

The src/app folder will now have a new service file with the name my-data-service.ts.

Inject the service into any component that needs to share data:

import { MyDataService } from './my-data.service';

constructor(private myDataService: MyDataService) { }

Once injected, the service will be available in the component as this.my data service.

To share data between components, simply use the setData() and getData() methods:

this.myDataService.setData('some data');

const data = this.myDataService.getData();
 

40. Describe the MVVM architecture.


A common architectural pattern in software engineering is called MVVM architecture. Model-View-ViewModel is what it stands for. A variant of the common MVC (Model-View-Controller) software design paradigm is called MVVM. The primary distinction between the two is that MVC distinguishes between data access logic and business logic, whereas MVVM distinguishes between user interface logic and business logic. The development, testing, and maintenance of software programmes are made simpler by the separation of concerns.

The MVVM architecture's Model layer is in charge of handling and storing data. It could be a local data source, a database, or a web service. The user's view of the data is handled by the View layer. It may take the form of a web page, command-line interface, or graphical user interface (GUI). User input is handled by the ViewModel layer, which is in charge of updating the View layer appropriately. The application's business logic is contained in it.

In conjunction with other software design patterns like Model-View-Presenter (MVP) and Model-View-Controller (MVC), the MVVM architecture is frequently employed (MVC). A whole software application can be made by combining these patterns.

For contemporary software applications, the MVVM design is a common option. It enables programmers to make apps that are easier to maintain and more responsive. MVVM design can also be utilised to build apps that are simple to convert to many platforms.












 

In Angular interview questions, what is a module?

The "Bootstrapping Module" in Angular is the root module used to launch or bootstrap the application. Every Angular project contains a Bootstrapping Module, which is kept in the AppModule class. In actuality, the AppModule is another name for the Bootstrapping module.

What does Angular's lazy loading mean?

When a specific route is active, Angular's lazy loading approach enables you to load JavaScript components asynchronously. By dividing the application into many bundles, it accelerates the application's load time. The bundles are loaded as needed when the user moves across the programme.

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