60+ Angular Interview Questions in 2025: Prepare Like a Pro

Angular Interview Questions For Advanced Level 

26. What is the difference between AOT and JIT? 

Ahead of Time (AOT) compilation converts your code during the build time before the browser downloads and runs that code. This ensures faster rendering to the browser. To specify AOT compilation, include the --aot option with the ng build or ng serve command. 

The Just-in-Time (JIT) compilation process is a way of compiling computer code to machine code during execution or run time. It is also known as dynamic compilation. JIT compilation is the default when you run the ng build or ng serve CLI commands. 

27. Explain the @Component Decorator.

TypeScript class is one that is used to create components. This genre of class is then decorated with the "@Component" decorator. The decorato’s purpose is to accept a metadata object that provides relevant information about the component.  

The image above shows an App component - a pure TypeScript class decorated with the “@Component” decorator. The metadata object that gets accepted by the decorator provides properties like templateUrl, selector, and others, where the templateUrL property points to an HTML file defining what you see on the application. 

28. What are Services in Angular? 

Angular Services perform tasks that are used by multiple components. These tasks could be data and image fetching, network connections, and database management among others. They perform all the operational tasks for the components and avoid rewriting of code. A service can be written once and injected into all the components that use that service. 

29. What are Promises and Observables in Angular? 

While both the concepts deal with Asynchronous events in Angular, Promises handle one such event at a time while observables handle a sequence of events over some time. 

Promises - They emit a single value at a time. They execute immediately after creation and are not cancellable. They are Push errors to the child promises. 

Observables - They are only executed when subscribed to them using the subscribe() method. They emit multiple values over a period of time. They help perform operations like forEach, filter, and retry, among others. They deliver errors to the subscribers. When the unsubscribe() method is called, the listener stops receiving further values.

30. What is ngOnInit? How is it defined? 

ngOnInit is a lifecycle hook and a callback method that is run by Angular to indicate that a component has been created. It takes no parameters and returns a void type.

export class MyComponent implements OnInit {

  constructor() { }

  ngOnInit(): void {

    //....

  }

}

31. How to use ngFor in a tag? 

The ngFor directive is used to build lists and tables in the HTML templates. In simple terms, this directive is used to iterate over an array or an object and create a template for each element. 

<ul> 

      <li *ngFor = "let items in itemlist"> {{ item }} </li>

    </ul>

1. “Let item” creates a local variable that will be available in the template
2. “Of items” indicates that we are iterating over the items iterable. 
3. The * before ngFor creates a parent template. 

32. What are Template and Reactive forms?

Template-driven approach

• In this method, the conventional form tag is used to create forms. Angular automatically interprets and creates a form object representation for the tag. 
• Controls can be added to the form using the NGModel tag. Multiple controls can be grouped using the NGControlGroup module. 
• A form value can be generated using the “form.value” object. Form data is exported as JSON values when the submit method is called. 
• Basic HTML validations can be used to validate the form fields. In the case of custom validations, directives can be used. 
• Arguably, this method is the simplest way to create an Angular App. 

Reactive Form Approach

• This approach is the programming paradigm oriented around data flows and propagation of change. 
• With Reactive forms, the component directly manages the data flows between the form controls and the data models. 
• Reactive forms are code-driven, unlike the template-driven approach. 
• Reactive forms break from the traditional declarative approach. 
• Reactive forms eliminate the anti-pattern of updating the data model via two-way data binding.
• Typically, Reactive form control creation is synchronous and can be unit tested with synchronous programming techniques. 

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

Bootstrap is a powerful toolkit. It is a collection of HTML, CSS, and JavaScript tools for creating and building responsive web pages and web applications.

There are two ways to embed the bootstrap library into your application. 

1. Angular Bootstrap via CDN - Bootstrap CDN is a public Content Delivery Network. It enables you to load the CSS and JavaScript files remotely from its servers. 
2. Angular Bootstrap via NPM - Another way to add Bootstrap to your Angular project is to install it into your project folder by using NPM (Node Package Manager). 

npm install bootstrap 

npm install jquery

34. What is Eager and Lazy loading? 

Eager loading is the default module-loading strategy. Feature modules under Eager loading are loaded before the application starts. This is typically used for small size applications.

Lazy loading dynamically loads the feature modules when there's a demand. This makes the application faster. It is used for bigger applications where all the modules are not required at the start of the application. 

35. What type of DOM does Angular implement? 

DOM (Document Object Model) treats an XML or HTML document as a tree structure in which each node is an object representing a part of the document. 

Angular uses the regular DOM. This updates the entire tree structure of HTML tags until it reaches the data to be updated. However, to ensure that the speed and performance are not affected, Angular implements Change Detection.

With this, you have reached the end of the article. We highly recommend brushing up on the core concepts for an interview. It’s always an added advantage to write the code in places necessary. 

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

Client-side frameworks like Angular were introduced to provide a more responsive user experience. By using a framework, developers can create web applications that are more interactive and therefore provide a better user experience.

Frameworks like Angular also make it easier for developers to create single-page applications (SPAs). SPAs are web applications that only need to load a single HTML page. This makes them much faster and more responsive than traditional web applications.

Overall, client-side frameworks like Angular were introduced in order to improve the user experience of web applications. By making web applications more responsive and easier to develop, they provide a better experience for both developers and users.

37. How does an Angular application work?

An Angular application is a Single Page Application, or SPA. This means that the entire application lives within a single page, and all of the resources (HTML, CSS, JavaScript, etc.) are loaded when the page is first loaded. Angular uses the Model-View-Controller, or MVC, architecture pattern to manage its data and views. The Model is the data that the application uses, the View is what the user sees, and the Controller is responsible for managing communication between the Model and the View.

When a user interacts with an Angular application, the Angular framework will automatically update the View to reflect any changes in the data. This means that Angular applications are very responsive and fast, as the user does not need to wait for the page to reload in order to see updated data.

Angular applications are also very scalable, as they can be divided into small modules that can be loaded independently of each other. This means that an Angular application can be easily extended with new functionality without having to rewrite the entire application.

Overall, Angular applications are very fast, responsive, and scalable. They are easy to develop and extend, and provide a great user experience.

The following is is an example of coding from an angular.json file:

 "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. Explain components, modules and services in Angular.

Components, modules and services are the three fundamental building blocks in Angular. Components are the smallest, self-contained units in an Angular application. They are typically used to represent a view or UI element, such as a button or a form input field. 

Code example:

import { Component, OnInit } from '@angular/core';

     @Component({

       selector: 'app-test',

       templateUrl: './test.component.html',

       styleUrls: ['./test.component.css']

     })

     export lass TestComponent implements OnInit {

       constructor() {}

       ngOnInit() {

       }

     }  

Modules are larger units that group together one or more related components. Services are singleton objects that provide specific functionality throughout an Angular application, such as data access or logging.

Code example:

import { BrowserModule } from '@angular/platform-browser';

      import { NgModule } from '@angular/core';

      import { AppComponent } from './app.component';

      import { TestComponent } from './test/text.component';

      @NgModule({

        declarations: [

          AppComponent,

          TestComponent

        ],

        imports: [

          BrowserModule

        ],

        providers: [],

        bootstrap: [AppComponent]

      })

      export class AppModule { }    

Each component in Angular has its own isolated scope. This means that a component's dependencies (services, other components, etc.) are not accessible to any other component outside of its own scope. This isolation is important for ensuring modularity and flexibility in an Angular application.

Services, on the other hand, are not isolated and can be injected into any other unit in an Angular application (component, module, service, etc.). This makes them ideal for sharing data or functionality across the entire app.

Code example:

import { Injectable } from '@angular/core';

      @Injectable({

        providedIn: 'root'

      })

      export class TestServiceService {

        constructor() { }

      }

When designing an Angular application, it is important to keep these three building blocks in mind. Components should be small and self-contained, modules should group together related components, and services should provide shared functionality across the entire app. By following this design principle, you can create an Angular application that is modular, flexible, and easy to maintain.

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39. How are Angular expressions different from JavaScript expressions?

One major difference between Angular expressions and JavaScript expressions is that Angular expressions are compiled while JavaScript expressions are not. This means that Angular expressions are more efficient since they're already pre-processed. Additionally, Angular expressions can access scope properties while JavaScript expressions cannot. Finally, Angular expressions support some additional features such as filters and directives which aren't available in JavaScript expressions.

Javascript expression example:

<!DOCTYPE html>

      <html lang="en">

      <head>

          <meta charset="UTF-8">

          <meta name="viewport" content="width=device-width, initial-scale=1.0">

          <title>JavaScript Test</title>

      </head>

      <body>

          <div id="foo"><div>

      </body>

      <script>

          'use strict';

          let bar = {};

          document.getElementById('foo').innerHTML = bar.x;

      </script>

      </html>

Angular expression example:

import { Component, OnInit } from '@angular/core';

      @Component({

        selector: 'app-new',

        template: `

            <h4>{{message}}</h4>

        `,

        styleUrls: ['./new.component.css']

      })

      export class NewComponent implements OnInit {

        message:object = {};

        constructor() { }

        ngOnInit() {

        }

      }

40. Angular by default, uses client-side rendering for its applications.

This means that the Angular application is rendered on the client-side — in the user's web browser. Client-side rendering has a number of advantages, including improved performance and better security. However, there are some drawbacks to using client-side rendering, as well. One of the biggest drawbacks is that it can make your application more difficult to debug.

Client-side rendering is typically used for applications that are not heavily data-driven. If your application relies on a lot of data from a server, client-side rendering can be very slow. Additionally, if you're using client-side rendering, it's important to be careful about how you load and cache your data. If you're not careful, you can easily end up with an application that is very slow and difficult to use. When rendered on the server-side, this is called Angular Universal.

41. How do you share data between components in Angular?

Sharing data between components in Angular is simple and easy. To share data, all you need to do is use the Angular CLI to generate a new service. This service can be injected into any component and will allow the components to share data.

To generate a new service, use the following Angular CLI command:

ng generate service my-data-service

This will create a new service file called my-data-service.ts in the src/app folder.

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.myDataService.

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

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

const data = this.myDataService.getData();

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42. Explain the concept of dependency injection.

Dependency injection is a technique used to create loosely coupled code. It allows pieces of code to be reused without the need for hard-coded dependencies. This makes code more maintainable and easier to test. Dependency injection is often used in frameworks like AngularJS, ReactJS, and VueJS. It is also possible to use dependency injection in vanilla JavaScript. To use dependency injection in JavaScript, you need a dependency injection library. There are many different libraries available, but they all work in basically the same way.

The first step is to create a dependency injection container. This is a simple object that will hold all of the dependencies that your code needs. Next, you need to register all of the dependencies that your code will need with the container. The registration process will vary depending on the library you are using, but it is usually just a matter of providing the dependency's name and constructor function.

Once all of the dependencies have been registered, you can then inject them into your code. The injection process will again vary depending on the library you are using, but it is usually just a matter of providing the dependency's name. The library will then take care of instantiating the dependency and passing it to your code.

Dependency injection can be a great way to make your code more modular and easier to maintain. It can also make it easier to unit test your code, as you can inject mock dependencies instead of the real ones. If you are using a framework that supports dependency injection, it is probably already being used in your code. If you are not using a framework, you can still use dependency injection by choosing a library and following the above steps.

import { Injectable } from '@angular/core';

     @Injectable({

       providedIn: 'root'

     })

     export class TestService {

       importantValue:number = 42;

       constructor() { }

       returnImportantValue(){

         return this.importantValue;

       }

     }

The injectable dependencies are created after adding the @Injectable decorator to a class. The dependency above is then injected into the following component:   

import { TestService } from './../test.service';

      import { Component, OnInit } from '@angular/core';

      @Component({

        selector: 'app-test',

        templateUrl: './test.component.html',

        styleUrls: ['./test.component.css']

      })

      export class TestComponent implements OnInit {

        value:number;

        constructor(private testService:TestService) { }

        ngOnInit() {

          this.value = this.testService.returnImportantValue();

        }

      }

43. Explain MVVM architecture.

MVVM architecture is an architectural pattern used mainly in software engineering. It stands for Model-View-ViewModel. MVVM is a variation of the traditional MVC (Model-View-Controller) software design pattern. The main difference between the two is that MVVM separates the user interface logic from the business logic, while MVC separates the data access logic from the business logic. This separation of concerns makes it easier to develop, test, and maintain software applications.

The Model layer in MVVM architecture is responsible for storing and managing data. It can be a database, a web service, or a local data source. The View layer is responsible for displaying data to the user. It can be a graphical user interface (GUI), a command-line interface (CLI), or a web page. The ViewModel layer is responsible for handling user input and updating the View layer accordingly. It contains the business logic of the application.

MVVM architecture is often used in conjunction with other software design patterns, such as Model-View-Presenter (MVP) and Model-View-Controller (MVC). These patterns can be used together to create a complete software application.

MVVM architecture is a popular choice for modern software applications. It allows developers to create applications that are more responsive and easier to maintain. Additionally, MVVM architecture can be used to create applications that can be easily ported to different platforms.

Angular Interview Questions for Experienced

44. What are RxJs in Angular?

RxJs is a library that provides reactive programming support for Angular applications. It allows you to work with asynchronous data streams and handle events over time. RxJs is based on Observables, which are data streams that can be subscribed to and processed using operators. It provides a powerful and flexible way to handle complex asynchronous operations in Angular.

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45. What exactly is a parameterized pipe?

A parameterized pipe in Angular is a pipe that accepts one or more arguments, also known as parameters. Pipes transform data in Angular templates, and parameterized pipes allow you to customize the transformation based on specific requirements. By passing parameters to a pipe, you can modify its behavior and apply different transformations to the data.

46. What are class decorators?

Class decorators in Angular are a type of decorator that can be applied to a class declaration. They are used to modify the behavior of the class or add additional functionality. Class decorators are defined using the @ symbol followed by the decorator name and are placed immediately before the class declaration. They can be used for various purposes, such as adding metadata, applying mixins, or extending the functionality of a class.

47. What are Method decorators?

Method decorators in Angular are decorators that can be applied to methods within a class. They are used to modify the behavior of the method or add additional functionality. Method decorators are defined using the @ symbol followed by the decorator name and are placed immediately before the method declaration. They can be used for tasks like logging, caching, or modifying the method's behavior based on specific conditions.

48. What are property decorators?

Property decorators in Angular are decorators that can be applied to class properties. They are used to modify the behavior of the property or add additional functionality. Property decorators are defined using the @ symbol followed by the decorator name and are placed immediately before the property declaration. They can be used for tasks like validation, memoization, or accessing metadata associated with the property.

49. What are router links?

Router links in Angular are used for navigation within an application. They are defined using the routerLink directive and provide a way to navigate to different routes or components. Router links can be used in HTML templates and are typically placed on anchor (<a>) tags or other clickable elements. By specifying the destination route or component, router links allow users to navigate between different parts of an Angular application.

50. What exactly is the router state?

The router state in Angular represents the current state of the Angular router. It contains information about the current route, including the URL, route parameters, query parameters, and other related data. The router state can be accessed and manipulated using the Angular Router service. It provides a way to programmatically navigate, retrieve information about the current route, and handle route changes in Angular applications.

51. What does Angular Material mean?

Angular Material is a UI component library for Angular applications. It provides a set of pre-built and customizable UI components, such as buttons, forms, navigation menus, and dialog boxes, that follow the Material Design guidelines. Angular Material simplifies the process of building consistent and visually appealing user interfaces in Angular. It offers a range of features and styles that can be easily integrated into Angular projects.

52. What is transpiling in Angular?

Transpiling in Angular refers to the process of converting TypeScript code into JavaScript code that web browsers can execute. Angular applications are built using TypeScript, a superset of JavaScript that adds static typing and additional features to the language. Since browsers can only run JavaScript, the TypeScript code needs to be transpiled into JavaScript before it can be executed. This is typically done using the TypeScript compiler (tsc) or build tools like Angular CLI.

53. What are HTTP interceptors?

HTTP interceptors in Angular are a feature that allows you to intercept HTTP requests and responses globally. Interceptors provide a way to modify or handle HTTP requests and responses at a centralized location before they reach the server or client. This can be useful for logging requests, adding authentication headers, handling errors, or modifying request/response data. Interceptors can be registered in the Angular module and are executed in a specific order based on the request/response pipeline.

54. What is Change Detection, and how does the Change Detection Mechanism work?

Change Detection in Angular is a mechanism that determines when and how to update the user interface based on changes in the application's data model. Angular uses a tree of change detectors to track changes in component properties and update the DOM accordingly. When a change occurs, Angular performs a change detection process, which involves checking each component's properties for changes and updating the DOM if necessary. The change detection mechanism keeps the UI in sync with the application's data.

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55. What is a bootstrapping module?

A bootstrapping module in Angular is the main entry point of an Angular application. It is responsible for starting the application and initializing the root component. The bootstrapping module is typically defined in the main.ts file and is configured in the Angular AppModule. It sets up the necessary environment, loads required modules, and invokes the Angular platform to start the application. The bootstrapping module plays a crucial role in the Angular application's lifecycle.

Angular Scenario Based Interview Questions

56. How do you choose anc from a component template?

You can use various techniques to choose an element from a component template in Angular. One common approach is to use template reference variables. The template defines these variables using the # symbol followed by a name. You can then reference the element using the variable name in your component code. Another approach is to use Angular directives like ViewChild or ViewChildren to query for elements based on CSS selectors or component types. These directives provide more flexibility and control when selecting elements from the component template.

57. How do you deal with errors in observables?

When dealing with errors in observables in Angular, catchError operator can be used to handle and recover from errors. This operator allows you to provide a fallback value or execute alternative logic when an error occurs. You can chain the catchError operator after the observable that might produce an error and define a callback function to handle the error. Within the callback function, you can perform error handling tasks such as logging the error, displaying an error message to the user, or initiating a retry mechanism.

58. How to include SASS into an Angular project?

To include SASS (Syntactically Awesome Style Sheets) into an Angular project, you need to install the required dependencies and configure the project accordingly. Follow these steps:

• Install the node-sass package by running the command npm install node-sass --save-dev.
• Update the angular.json file in your project's root directory.
• Locate the styles property under architect > build > options.
• Change the file extension from .css to .scss to indicate that you are using SASS.
• Rename your existing CSS files to SCSS files (e.g., styles.css to styles.scss).
• Restart the Angular development server for the changes to take effect.

Once SASS is included in your Angular project, you can write your styles using SASS syntax, which provides additional features like variables, mixins, and nested selectors.

59. What happens when we use the script tag within a template?

Using the script tag within an Angular template is not a recommended practice. Angular templates are intended for defining the structure and layout of the user interface, and including scripts directly within the template goes against the separation of concerns principle. When a script tag is used within a template, the browser treats it as part of the HTML content and attempts to execute it. However, Angular's template compiler does not process or execute scripts within templates. Instead, scripts should be placed in separate JavaScript files and included using the appropriate Angular mechanisms, such as component logic or Angular modules.

60. Write a code to share data from the Parent to Child Component?

To share data from a parent component to a child component in Angular, you can make use of input properties. Input properties allow you to pass data from parent to child components. Here's an example:

Parent Component:

typescript

Copy code

import { Component } from '@angular/core';

@Component({

  selector: 'app-parent',

  template: `

    <app-child [message]="parentMessage"></app-child>

  `,

})

export class ParentComponent {

  parentMessage = 'Hello from parent';

}

Child Component:

typescript

Copy code

import { Component, Input } from '@angular/core';

@Component({

  selector: 'app-child',

  template: `

    <p>{{ message }}</p>

  `,

})

export class ChildComponent {

  @Input() message: string;

}

In this example, the parent component (ParentComponent) defines a property parentMessage that holds the data to be shared with the child component (ChildComponent). The parent component then passes this data to the child component using the input property [message]. The child component receives the data through the @Input() decorator and can use it within its template or logic.

61. Create a TypeScript class with a constructor and a function.

Here's an example of a TypeScript class with a constructor and a function:

typescript
Copy code
class Person {
  name: string;
  age: number;
  constructor(name: string, age: number) {
    this.name = name;
    this.age = age;
  }
  sayHello() {
    console.log(`Hello, my name is ${this.name} and I'm ${this.age} years old.`);
  }
}
// Usage
const person = new Person('John', 30);
person.sayHello();

In this example, the Person class represents a person with a name and an age property. The constructor is used to initialize these properties when creating an instance of the class. The sayHello function is a method of the class that logs a greeting message using the person's name and age. Finally, an instance of the Person class is created, and the sayHello function is called to output the greeting message.

Next Steps 

We hope that this article on Angular Interview Questions helped you understand the type of questions asked and how to answer them. But, if you wish to learn Angular and perhaps make a career out of it, certification will come in handy.

You can also explore and get familiar with interview questions related to other frontend languages like Angular, CSS or ReactJS interview questions.

Simplilearn's Angular Certification Training Course helps you master front-end web development with Angular. You will learn the knack of creating applications with the help of concepts like facilitating the development of single-page web applications, components, typescript, dependency injection, and directives with this course. The course also includes a real-time project to test your skills. 

If you are looking to enhance your software development skills, we recommend you check out Simplilearn's Full Stack Developer—MERN Stack Course. This course can help you hone the right skills and become job-ready.

Do you have any questions for us? If you have feedback or questions, drop us a comment in the comments section of this Angular interview questions tutorial. Our experts will get back to you as soon as possible! 

FAQs

1. What are the key concepts of Angular?

Some key concepts of Angular include components, modules, templates, data binding, services, dependency injection, and routing. These concepts form the foundation of Angular development and help in building dynamic and scalable web applications.

2. What is Angular coding language?

Angular itself is not a coding language. It is a framework for building web applications using TypeScript. TypeScript is a superset of JavaScript that adds static typing and additional features to JavaScript. Angular leverages TypeScript to provide a more structured and scalable approach to web development.

3. What is a service in Angular interview questions?

In Angular, a service is a class that is used to share data or functionality across different components. Services are responsible for providing specific functionality that can be used by multiple components in an application. They promote reusability, modularity, and maintainability in Angular projects.

4. What is the full form of ng in Angular?

In Angular, "ng" stands for "Angular". It is a convention used in Angular to prefix directives, components, and other Angular-specific entities. For example, ngFor is a built-in Angular directive used for rendering lists based on an array, and ngModel is a directive used for two-way data binding between an input element and a component property. The "ng" prefix helps to distinguish Angular-specific entities from regular HTML elements and attributes.