angular-interview-questions

List of 300 Angular Interview Questions and answers

Last updated Jul 8, 2026

4.9k

Stars

2.2k

Forks

Issues

Stars/day

Attention Score

View on GitHub ↗ Open in github.dev

Topics

#angular #angular-interview-questions #angular6 #angular7 #angularjs #interview-questions #javascript-framework #javascript-interview-questions #rxjs #typescript

Language breakdown

No language data available.

▸ Files click to expand

README

Angular Interview Questions & Answers

Click :star: if you like the project and follow @SudheerJonna for technical updates.

I recommend this Angular course to become top 10% at Angular (and build enterprise-level apps) and this coding interview bootcamp to ace your coding interview and actually get hired.

### What is Angular Framework?

Angular is a TypeScript-based open-source front-end platform that makes it easy to build web, mobile and desktop applications. The major features of this framework include declarative templates, dependency injection, end to end tooling which ease application development.

⬆ Back to Top

### What is the difference between AngularJS and Angular?

AngularJS (version 1.x) is a JavaScript framework, whereas Angular (version 2+) is a complete rewrite of AngularJS using TypeScript, providing better performance, mobile support, modularity, and a more modern architecture.

Here are some of the major differences in tabular format:-

| AngularJS | Angular | |---- | --------- | It is based on MVC architecture| This is based on Service/Controller| | It uses JavaScript to build the application| Uses TypeScript to build the application| | Based on controllers concept| This is a component based UI approach| | No support for mobile platforms| Fully supports mobile platforms| | Difficult to build SEO friendly application| Ease to build SEO friendly applications|

⬆ Back to Top

### What is TypeScript?

TypeScript is a strongly typed superset of JavaScript created by Microsoft that adds optional types, classes, async/await and many other features, and compiles to plain JavaScript. Angular is written entirely in TypeScript as a primary language. You can install TypeScript globally as

npm install -g typescript

Let's see a simple example of TypeScript usage:-

function greeter(person: string) {
        return "Hello, " + person;
    }
let user = "Sudheer";
document.body.innerHTML = greeter(user);

The greeter method allows only string type as argument.

⬆ Back to Top

### Write a pictorial diagram of Angular architecture?

The main building blocks of an Angular application are shown in the diagram below:- ScreenShot

⬆ Back to Top

### What are the key components of Angular?

Angular has the key components below, 1. Component: These are the basic building blocks of an Angular application to control HTML views. 2. Modules: An Angular module is a set of angular basic building blocks like components, directives, services etc. An application is divided into logical pieces and each piece of code is called as "module" which perform a single task. 3. Templates: These represent the views of an Angular application. 4. Services: Are used to create components which can be shared across the entire application. 5. Metadata: This can be used to add more data to an Angular class.

⬆ Back to Top

### What are directives?

Directives add behaviour to an existing DOM element or an existing component instance.

import { Directive, ElementRef, Input } from '@angular/core';
@Directive({ selector: '[myHighlight]' })     export class HighlightDirective {         constructor(el: ElementRef) {            el.nativeElement.style.backgroundColor = 'yellow';         }     }

Now this directive extends HTML element behavior with a yellow background as below

<p myHighlight>Highlight me!</p>

⬆ Back to Top

### What are components?

Components are the most basic UI building block of an Angular app, which form a tree of Angular components. These components are a subset of directives. Unlike directives, components always have a template, and only one component can be instantiated per element in a template. Let's see a simple example of Angular component

import { Component } from '@angular/core';
@Component ({        selector: 'my-app',        template:  &lt;div&gt;           &lt;h1&gt;{{title}}&lt;/h1&gt;           &lt;div&gt;Learn Angular6 with examples&lt;/div&gt;        &lt;/div&gt; ,     })
export class AppComponent {        title: string = 'Welcome to Angular world';     }

⬆ Back to Top

### What are the differences between Component and Directive?

In a short note, A component(@component) is a directive-with-a-template.

Some of the major differences are mentioned in a tabular form

| Component | Directive | |---- | --------- | To register a component we use @Component meta-data annotation | To register a directive we use @Directive meta-data annotation | | Components are typically used to create UI widgets| Directives are used to add behavior to an existing DOM element | | Component is used to break down the application into smaller components| Directive is used to design re-usable components| | Only one component can be present per DOM element | Many directives can be used per DOM element | | @View decorator or templateurl/template are mandatory | Directive doesn't use View|

⬆ Back to Top

### What is a template?

A template is a HTML view where you can display data by binding controls to properties of an Angular component. You can store your component's template in one of two places. You can define it inline using the template property, or you can define the template in a separate HTML file and link to it in the component metadata using the @Component decorator's templateUrl property.

Using inline template with template syntax,

import { Component } from '@angular/core';
@Component ({        selector: 'my-app',        template: '           <div>              <h1>{{title}}</h1>              <div>Learn Angular</div>           </div>        '     })
export class AppComponent {        title: string = 'Hello World';     }

Using separate template file such as app.component.html

import { Component } from '@angular/core';
@Component ({        selector: 'my-app',        templateUrl: 'app/app.component.html'     })
export class AppComponent {        title: string = 'Hello World';     }

⬆ Back to Top

### What is a module?

Modules are logical boundaries in your application and the application is divided into separate modules to separate the functionality of your application. Lets take an example of app.module.ts root module declared with @NgModule decorator as below,

import { NgModule }      from '@angular/core';
    import { BrowserModule } from '@angular/platform-browser';
    import { AppComponent }  from './app.component';
@NgModule ({        imports:      [ BrowserModule ],        declarations: [ AppComponent ],        bootstrap:    [ AppComponent ],        providers: []     })     export class AppModule { }

The NgModule decorator has five important (among all) options: 1. The imports option is used to import other dependent modules. The BrowserModule is required by default for any web based angular application. 2. The declarations option is used to define components in the respective module. 3. The bootstrap option tells Angular which Component to bootstrap in the application. 4. The providers option is used to configure a set of injectable objects that are available in the injector of this module. 5. The entryComponents option is a set of components dynamically loaded into the view.

⬆ Back to Top

### What are lifecycle hooks available?

Angular application goes through an entire set of processes or has a lifecycle right from its initiation to the end of the application. The representation of lifecycle in pictorial representation as follows,

ScreenShot

The description of each lifecycle method is as below, 1. ngOnChanges: When the value of a data bound property changes, then this method is called. 2. ngOnInit: This is called whenever the initialization of the directive/component after Angular first displays the data-bound properties happens. 3. ngDoCheck: This is for the detection and to act on changes that Angular can't or won't detect on its own. 4. ngAfterContentInit: This is called in response after Angular projects external content into the component's view. 5. ngAfterContentChecked: This is called in response after Angular checks the content projected into the component. 6. ngAfterViewInit: This is called in response after Angular initializes the component's views and child views. 7. ngAfterViewChecked: This is called in response after Angular checks the component's views and child views. 8. ngOnDestroy: This is the cleanup phase just before Angular destroys the directive/component.

⬆ Back to Top

### What is a data binding?

Data binding is a core concept in Angular and allows to define communication between a component and the DOM, making it very easy to define interactive applications without worrying about pushing and pulling data. There are four forms of data binding(divided as 3 categories) which differ in the way the data is flowing. 1. From the Component to the DOM:

Interpolation: {{ value }}: Adds the value of a property from the component

<li>Name: {{ user.name }}</li>         <li>Address: {{ user.address }}</li>

Property binding: [property]=”value”: The value is passed from the component to the specified property or simple HTML attribute

<input type="email" [value]="user.email">

2. From the DOM to the Component: Event binding: (event)=”function”: When a specific DOM event happens (eg.: click, change, keyup), call the specified method in the component

<button (click)="logout()"></button>

3. Two-way binding: Two-way data binding: [(ngModel)]=”value”: Two-way data binding allows to have the data flow both ways. For example, in the below code snippet, both the email DOM input and component email property are in sync

<input type="email" [(ngModel)]="user.email">

⬆ Back to Top

### What is metadata?

Metadata is used to decorate a class so that it can configure the expected behavior of the class. The metadata is represented by decorators 1. Class decorators, e.g. @Component and @NgModule

import { NgModule, Component } from '@angular/core';
@Component({           selector: 'my-component',           template: '<div>Class decorator</div>',         })         export class MyComponent {           constructor() {             console.log('Hey I am a component!');           }         }
@NgModule({           imports: [],           declarations: [],         })         export class MyModule {           constructor() {             console.log('Hey I am a module!');           }         }

2. Property decorators Used for properties inside classes, e.g. @Input and @Output

import { Component, Input } from '@angular/core';
@Component({             selector: 'my-component',             template: '<div>Property decorator</div>'         })
export class MyComponent {             @Input()             title: string;         }

3. Method decorators Used for methods inside classes, e.g. @HostListener

import { Component, HostListener } from '@angular/core';
@Component({             selector: 'my-component',             template: '<div>Method decorator</div>'         })         export class MyComponent {             @HostListener('click', ['$event'])             onHostClick(event: Event) {                 // clicked, event available             }         }

4. Parameter decorators Used for parameters inside class constructors, e.g. @Inject, @Optional

import { Component, Inject } from '@angular/core';         import { MyService } from './my-service';
@Component({             selector: 'my-component',             template: '<div>Parameter decorator</div>'         })         export class MyComponent {             constructor(@Inject(MyService) myService) {                 console.log(myService); // MyService             }         }
// Angular v18 and above
import { Component, inject } from '@angular/core';         import { MyService } from './my-service';
@Component({             selector: 'my-component',             template: '<div>Parameter decorator</div>'         })         export class MyComponent {         myService: MyService = inject(MyService)             constructor() {                 console.log(myService); // MyService             }         }

⬆ Back to Top

### What is angular CLI?

Angular CLI(Command Line Interface) is a command line interface to scaffold and build angular apps using nodejs style (commonJs) modules. You need to install using below npm command,

npm install @angular/cli@latest

Below are the list of few commands, which will come handy while creating angular projects 1. Creating New Project: ng new

2. Generating Components, Directives & Services: ng generate/g The different types of commands would be, * ng generate class my-new-class: add a class to your application * ng generate component my-new-component: add a component to your application * ng generate directive my-new-directive: add a directive to your application * ng generate enum my-new-enum: add an enum to your application * ng generate module my-new-module: add a module to your application * ng generate pipe my-new-pipe: add a pipe to your application * ng generate service my-new-service: add a service to your application

3. Running the Project: ng serve

⬆ Back to Top

### What is the difference between constructor and ngOnInit?

The Constructor is a default method of the class that is executed when the class is instantiated and ensures proper initialisation of fields in the class and its subclasses. Angular, or better Dependency Injector (DI), analyses the constructor parameters and when it creates a new instance by calling new MyClass() it tries to find providers that match the types of the constructor parameters, resolves them and passes them to the constructor. ngOnInit is a life cycle hook called by Angular to indicate that Angular is done creating the component. Mostly we use ngOnInit for all the initialization/declaration and avoid stuff to work in the constructor. The constructor should only be used to initialize class members but shouldn't do actual "work". So you should use constructor() to setup Dependency Injection and not much else. ngOnInit() is better place to "start" - it's where/when components' bindings are resolved.

export class App implements OnInit{
      constructor(private myService: MyService){
         //called first time before the ngOnInit()
      }
ngOnInit(){          //called after the constructor and called  after the first ngOnChanges()          //e.g. http call...       }     }

⬆ Back to Top

### What is a service?

A service is used when a common functionality needs to be provided to various modules. Services allow for greater separation of concerns for your application and better modularity by allowing you to extract common functionality out of components.

Let's create a repoService which can be used across components,

import { Injectable } from '@angular/core';
    import { Http } from '@angular/http';
@Injectable({ // The Injectable decorator is required for dependency injection to work       // providedIn option registers the service with a specific NgModule       providedIn: 'root',  // This declares the service with the root app (AppModule)     })     export class RepoService{       constructor(private http: Http){       }
fetchAll(){         return this.http.get('https://api.github.com/repositories');       }     }

The above service uses Http service as a dependency.

⬆ Back to Top

### What is dependency injection in Angular?

Dependency injection (DI), is an important application design pattern in which a class asks for dependencies from external sources rather than creating them itself. Angular comes with its own dependency injection framework for resolving dependencies( services or objects that a class needs to perform its function).So you can have your services depend on other services throughout your application.

⬆ Back to Top

### How is Dependency Hierarchy formed?

Injectors in Angular have rules that can be leveraged to achieve the desired visibility of injectables in your applications. By understanding these rules, you can determine in which NgModule, Component, or Directive you should declare a provider.

#### Angular has two injector hierarchies: Screenshot

#### Module injector When angular starts, it creates a root injector where the services will be registered, these are provided via injectable annotation. All services provided in the ng-model property are called providers (if those modules are not lazy-loaded).

Angular recursively goes through all models which are being used in the application and creates instances for provided services in the root injector. If you provide some service in an eagerly-loaded model, the service will be added to the root injector, which makes it available across the whole application.

#### Platform Module During application bootstrapping angular creates a few more injectors, above the root injector goes the platform injector, this one is created by the platform browser dynamic function inside the main.ts file, and it provides some platform-specific features like DomSanitizer.

#### NullInjector() At the very top, the next parent injector in the hierarchy is the NullInjector().The responsibility of this injector is to throw the error if something tries to find dependencies there, unless you've used @Optional() because ultimately, everything ends at the NullInjector() and it returns an error or, in the case of @Optional(), null.

Screenshot

#### ElementInjector Angular creates ElementInjector hierarchies implicitly for each DOM element. ElementInjector injector is being created for any tag that matches the angular component, or any tag on which directive is applied, and you can configure it in component and directive annotations inside the provider's property, thus, it creates its own hierarchy likewise the upper one.

Screenshot

⬆ Back to Top

### What is the purpose of async pipe?

The AsyncPipe subscribes to an observable or promise and returns the latest value it has emitted. When a new value is emitted, the pipe marks the component to be checked for changes.

Let's take a time observable which continuously updates the view for every 2 seconds with the current time.

@Component({       selector: 'async-observable-pipe',       template: &lt;div&gt;&lt;code&gt;observable|async&lt;/code&gt;:            Time: {{ time | async }}&lt;/div&gt;     })     export class AsyncObservablePipeComponent {       time: Observable<string>;       constructor() {         this.time = new Observable((observer) => {           setInterval(() => {             observer.next(new Date().toString());           }, 2000);         });       }     }

⬆ Back to Top

### What is the option to choose between inline and external template file?

You can store your component's template in one of two places. You can define it inline using the template property, or you can define the template in a separate HTML file and link to it in the component metadata using the @Component decorator's templateUrl property.

The choice between inline and separate HTML is a matter of taste, circumstances, and organization policy. But normally we use inline template for small portion of code and external template file for bigger views. By default, the Angular CLI generates components with a template file. But you can override that with the below command,

ng generate component hero -it

⬆ Back to Top

### What is the purpose of *ngFor directive?

We use Angular *ngFor directive in the template to display each item in the list. For example, here we can iterate over a list of users:

<li *ngFor="let user of users">
      {{ user }}
    </li>

The user variable in the *ngFor double-quoted instruction is a template input variable.

⬆ Back to Top

### What is the purpose of *ngIf directive?

Sometimes an app needs to display a view or a portion of a view only under specific circumstances. The Angular *ngIf directive inserts or removes an element based on a truthy/falsy condition. Let's take an example to display a message if the user age is more than 18:

<p *ngIf="user.age > 18">You are not eligible for student pass!</p>

Note: Angular isn't showing and hiding the message. It is adding and removing the paragraph element from the DOM. That improves performance, especially in the larger projects with many data bindings.

⬆ Back to Top

### What happens if you use script tag inside template?

Angular recognizes the value as unsafe and automatically sanitizes it, which removes the script tag but keeps safe content such as the text content of the script tag. This way it eliminates the risk of script injection attacks. If you still use it then it will be ignored and a warning appears in the browser console.

Let's take an example of innerHtml property binding which causes XSS vulnerability,

export class InnerHtmlBindingComponent {       // For example, a user/attacker-controlled value from a URL.       htmlSnippet = 'Template  <b>Syntax</b>';     }

⬆ Back to Top

### What is interpolation?

Interpolation is a special syntax that Angular converts into property binding. It’s a convenient alternative to property binding. It is represented by double curly braces({{}}). The text between the braces is often the name of a component property. Angular replaces that name with the string value of the corresponding component property.

Let's take an example,

<h3>       {{title}}       <img src="{{url}}" style="height:30px">     </h3>

In the example above, Angular evaluates the title and url properties and fills in the blanks, first displaying a bold application title and then a URL.

⬆ Back to Top

### What are template expressions?

A template expression produces a value similar to any Javascript expression. Angular executes the expression and assigns it to a property of a binding target; the target might be an HTML element, a component, or a directive. In the property binding, a template expression appears in quotes to the right of the = symbol as in [property]="expression". In interpolation syntax, the template expression is surrounded by double curly braces. For example, in the below interpolation, the template expression is {{username}},

<h3>{{username}}, welcome to Angular</h3>

The below javascript expressions are prohibited in template expression 1. assignments (=, +=, -=, ...) 2. new 3. chaining expressions with ; or , 4. increment and decrement operators (++ and --) ----------------------------------

⬆ Back to Top

### What are template statements?

A template statement responds to an event raised by a binding target such as an element, component, or directive. The template statements appear in quotes to the right of the = symbol like (event)="statement".

Let's take an example of button click event's statement

<button (click)="editProfile()">Edit Profile</button>

In the above expression, editProfile is a template statement. The below JavaScript syntax expressions are not allowed. 1. new 2. increment and decrement operators, ++ and -- 3. operator assignment, such as += and -= 4. the bitwise operators | and & 5. the template expression operators --------------------------------------

⬆ Back to Top

### How do you categorize data binding types?

Binding types can be grouped into three categories distinguished by the direction of data flow. They are listed as below, 1. From the source-to-view 2. From view-to-source 3. View-to-source-to-view

The possible binding syntax can be tabularized as below,

| Data direction | Syntax | Type | |---- | --------- | ---- | | From the source-to-view(One-way) | 1. {{expression}} 2. [target]="expression" 3. bind-target="expression" | Interpolation, Property, Attribute, Class, Style| | From view-to-source(One-way) | 1. (target)="statement" 2. on-target="statement" | Event | | View-to-source-to-view(Two-way)| 1. [(target)]="expression" 2. bindon-target="expression"| Two-way |

⬆ Back to Top

### What are pipes?

Pipes are simple functions that use template expressions to accept data as input and transform it into a desired output. For example, let us take a pipe to transform a component's birthday property into a human-friendly date using date pipe.

import { Component } from '@angular/core';
@Component({       selector: 'app-birthday',       template: &lt;p&gt;Birthday is {{ birthday | date }}&lt;/p&gt;     })     export class BirthdayComponent {       birthday = new Date(1987, 6, 18); // June 18, 1987     }

⬆ Back to Top

### What is a parameterized pipe?

A pipe can accept any number of optional parameters to fine-tune its output. The parameterized pipe can be created by declaring the pipe name with a colon ( : ) and then the parameter value. If the pipe accepts multiple parameters, separate the values with colons. Let's take a birthday example with a particular format(dd/MM/yyyy):

import { Component } from '@angular/core';
@Component({           selector: 'app-birthday',           template: &lt;p&gt;Birthday is {{ birthday | date:&#39;dd/MM/yyyy&#39;}}&lt;/p&gt; // 18/06/1987         })         export class BirthdayComponent {           birthday = new Date(1987, 6, 18);         }

Note: The parameter value can be any valid template expression, such as a string literal or a component property.

⬆ Back to Top

### How do you chain pipes?

You can chain pipes together in potentially useful combinations as per the needs. Let's take a birthday property which uses date pipe(along with parameter) and uppercase pipes as below

import { Component } from '@angular/core';
@Component({               selector: 'app-birthday',               template: &lt;p&gt;Birthday is {{  birthday | date:&#39;fullDate&#39; | uppercase}} &lt;/p&gt; // THURSDAY, JUNE 18, 1987             })             export class BirthdayComponent {               birthday = new Date(1987, 6, 18);             }

⬆ Back to Top

### What is a custom pipe?

Apart from built-in pipes, you can write your own custom pipe with the below key characteristics: 1. A pipe is a class decorated with pipe metadata @Pipe decorator, which you import from the core Angular library For example,

@Pipe({name: 'myCustomPipe'})

2. The pipe class implements the PipeTransform interface's transform method that accepts an input value followed by optional parameters and returns the transformed value. The structure of PipeTransform would be as below,

interface PipeTransform {
          transform(value: any, ...args: any[]): any
        }

3. The @Pipe decorator allows you to define the pipe name that you'll use within template expressions. It must be a valid JavaScript identifier.

template: {{someInputValue | myCustomPipe: someOtherValue}}

⬆ Back to Top

### Give an example of custom pipe?

You can create custom reusable pipes for the transformation of existing value. For example, let us create a custom pipe for finding file size based on an extension,

import { Pipe, PipeTransform } from '@angular/core';
@Pipe({name: 'customFileSizePipe'})         export class FileSizePipe implements PipeTransform {           transform(size: number, extension: string = 'MB'): string {             return (size / (1024 * 1024)).toFixed(2) + extension;           }         }

Now you can use the above pipe in template expression as below,

template:              &lt;h2&gt;Find the size of a file&lt;/h2&gt;             &lt;p&gt;Size: {{288966 | customFileSizePipe: &#39;GB&#39;}}&lt;/p&gt;

⬆ Back to Top

### What is the difference between pure and impure pipe?

A pure pipe is only called when Angular detects a change in the value or the parameters passed to a pipe. For example, any changes to a primitive input value (String, Number, Boolean, Symbol) or a changed object reference (Date, Array, Function, Object). An impure pipe is called for every change detection cycle no matter whether the value or parameters changes. i.e, An impure pipe is called often, as often as every keystroke or mouse-move.

⬆ Back to Top

### What is a bootstrapping module?

Every application has at least one Angular module, the root module that you bootstrap to launch the application is called as bootstrapping module. It is commonly known as AppModule. The default structure of AppModule generated by AngularCLI would be as follows:

import { BrowserModule } from '@angular/platform-browser';
        import { NgModule } from '@angular/core';
        import { FormsModule } from '@angular/forms';
        import { HttpClientModule } from '@angular/common/http';
import { AppComponent } from './app.component';
/ the AppModule class with the @NgModule decorator /         @NgModule({           declarations: [             AppComponent           ],           imports: [             BrowserModule,             FormsModule,             HttpClientModule           ],           providers: [],           bootstrap: [AppComponent]         })         export class AppModule { }

⬆ Back to Top

### What are observables?

Observables are declarative which provide support for passing messages between publishers and subscribers in your application. They are mainly used for event handling, asynchronous programming, and handling multiple values. In this case, you define a function for publishing values, but it is not executed until a consumer subscribes to it. The subscribed consumer then receives notifications until the function completes, or until they unsubscribe.

⬆ Back to Top

### What is HttpClient and its benefits?

Most of the Front-end applications communicate with backend services over HTTP protocol using either XMLHttpRequest interface or the fetch() API. Angular provides a simplified client HTTP API known as HttpClient which is based on top of XMLHttpRequest interface. This client is available from @angular/common/http package. You can import in your root module as below:

import { HttpClientModule } from '@angular/common/http';

The major advantages of HttpClient can be listed as below, 1. Contains testability features 2. Provides typed request and response objects 3. Intercept request and response 4. Supports Observable APIs 5. Supports streamlined error handling

⬆ Back to Top

### Explain on how to use HttpClient with an example?

Below are the steps need to be followed for the usage of HttpClient. 1. Import HttpClient into root module:

import { HttpClientModule } from '@angular/common/http';
        @NgModule({
          imports: [
            BrowserModule,
            // import HttpClientModule after BrowserModule.
            HttpClientModule,
          ],
          ......
          })
         export class AppModule {}

2. Inject the HttpClient into the application: Let's create a userProfileService(userprofile.service.ts) as an example. It also defines get method of HttpClient: ```javascript import { Injectable } from '@angular/core'; import { HttpClient } from '@angular/common/http';

const userProfileUrl

README truncated. View on GitHub

🔗 More in this category

Angular Interview Questions & Answers

Table of Contents