Top Angular Interview Questions And Answers 2023
1. What is Angular?
Answer: Angular is an open-source front-end framework developed by Google. It's used for building dynamic, single-page web applications (SPAs).
2. What's the difference between AngularJS and Angular?
Answer: AngularJS is the older version (1.x) of Angular, while Angular refers to Angular 2 and later versions. AngularJS is javascript based while Angular is typescript based.
3. Explain the basic architecture of an Angular application.
Answer: An Angular application consists of modules, components, services, templates, and directives. Modules encapsulate related functionality, components define the UI, services handle business logic, templates define the view, and directives add behavior to the DOM elements.
4. What are modules in Angular?
Answer: modules are the fundamental building blocks of an Angular application. They are used to organize and encapsulate related components, services, and directives. NgModule decorator is used to define and configure modules.
import { NgModule } from '@angular/core';
@NgModule({
declarations: [ /* List of components, directives, and pipes belonging to this module */ ],
imports: [ /* List of other modules that this module depends on */ ],
providers: [ /* List of services available to the components in this module */ ],
bootstrap: [ /* List of the root component(s) for bootstrapping the application */ ]
})
export class MyModule { }5. What is a component in Angular?
Answer: A component is a fundamental building block of an Angular application. It represents a piece of the user interface with its own logic and template. Components communicate with each other using inputs, outputs, and services. A component is typically composed of three main parts:
(a). Template: The template defines the structure of the component's UI using HTML along with Angular-specific syntax. The template specifies how the component's data should be displayed and manipulated.
(b). Class: The class defines the logic and behavior of the component using TypeScript. It contains properties and methods that handle data manipulation, interactions, and other business logic.
(c). Metadata: The metadata is defined using a decorator, usually the @Component decorator. It provides additional information about the component, such as its selector, template, styles, and more.
import { Component } from '@angular/core';
@Component({
selector: 'app-greeting',
template: '<h1>Hello, {{ name }}!</h1>',
styles: ['h1 { color: blue; }']
})
export class GreetingComponent {
name: string = 'John';
}6. What are directives in Angular?
Answer: Directives are used to extend and modify the behavior of HTML elements and components. They are used to add custom behavior and manipulate the DOM. Angular provides two main types of directives.
Attribute Directives: Attribute directives change the appearance or behavior of an element by manipulating its attributes or adding new behavior.
Examples:-
(a). ngStyle: Changes the style of an element based on specified conditions.
(b). ngClass: Adds or removes CSS classes based on certain conditions.
(c). ngModel: Binds a form input element (like input, textarea, or select) and a property in a component's class.
Structural Directives: Structural directives change the structure of the DOM by adding, removing, or manipulating elements.
Examples:-
(a). ngFor: Loops over an iterable (like an array) and creates a template for each item.
(b). ngWhile: Conditionally renders elements repeatedly while a condition is true.
(c). ngIf: Conditionally renders or removes an element from the DOM based on a condition.
(d). ngSwitch: Conditionally renders one element from a set of elements based on a provided value.
7. What are the differences between Component and Directive?
Answer: Components are the building blocks for creating user interface elements with their own templates and logic, while directives are used to modify the behavior or appearance of existing DOM elements.
8. Explain data binding in Angular.
Answer: Data binding is a powerful feature that allows you to establish a connection between your component and the DOM (template). There are one-way (interpolation, property binding, event binding) and two-way (ngModel) bindings.
Interpolation (One-Way Binding):
Interpolation is the simplest form of data binding and is denoted by double curly braces {{ }} in your template. It allows you to display component data in the template.
Example:
<p>{{ message }}</p>
Property Binding (One-Way Binding):
Property binding allows you to set the value of an HTML element's property based on a component's property. It is denoted by square brackets [ ] in your template.
Example:
<img [src]="imageUrl">
Event Binding (One-Way Binding):
Event binding allows you to respond to events triggered by UI elements (e.g., button clicks, mouse events) and execute methods in your component class. It is denoted by parentheses ( ) in your template.
Example:
<button (click)="onButtonClick()">Click me</button>
Two-Way Data Binding ([(ngModel)]):
Two-way data binding combines property binding and event binding to achieve synchronization between a form input element and a component property. It is denoted by [(ngModel)] in your template.
Example:
<input type="text" [(ngModel)]="userName">9. What is Two-Way Data Binding?
Answer: Two-Way Data Binding is a powerful feature in Angular that allows you to establish a bidirectional synchronization between a form input element and a property in your component class. This means that changes made in the UI element are automatically reflected in the component's property, and vice versa. Two-Way Data Binding combines both property binding and event binding to achieve this synchronization.
10. What is a service in Angular?
Answer: A service is a singleton object that handles business logic, data sharing, and communication between components.
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root'
})
export class DataService {
private data: string[] = [];
addData(item: string): void {
this.data.push(item);
}
getData(): string[] {
return this.data;
}
}
11. What is singleton object?
Answer: A singleton object refers to an instance of a class that is created only once during the lifetime of an application. This single instance is then shared and used across various parts of the application that require access to that object.
12. What is dependency injection in Angular?
Answer: Dependency Injection (DI) is a design pattern that is used to provide instances of services, components, and other objects to classes from external sources rather than creating them.
In short, dependency injection is a design pattern in which a class receives its dependencies from external sources rather than creating them.
In short, dependency injection is a design pattern in which a class receives its dependencies from external sources rather than creating them.
import { Component } from '@angular/core';
import { DataService } from './data.service';
@Component({
selector: 'app-home',
template: '...',
})
export class HomeComponent {
constructor(private dataService: DataService) {
// dataService instance is injected and available here
}
}
13. What is lazy loading in Angular?
Answer: Lazy loading is a powerful technique of loading components, modules, or assets only when they are actually needed, rather than loading them all at once when the application initially loads.
This approach can significantly improve the performance and loading speed of your application, especially in scenarios where you have large components or resources that are not immediately required.
To implement lazy loading in Angular, you need to configure your application's routing and organize your code into feature modules. loadChildren property is used to specify which module should be lazy-loaded.
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
const routes: Routes = [
{ path: 'home', loadChildren: () => import('./home/home.module').then(m => m.HomeModule) },
{ path: 'products', loadChildren: () => import('./products/products.module').then(m => m.ProductsModule) },
// ...other routes
];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule],
})
export class AppRoutingModule {}
14. How do you pass data from a parent component to a child component?
Answer: You can use Input properties to pass data from a parent component to a child component.
Parent Component (parent.component.ts):
import { Component } from '@angular/core';
@Component({
selector: 'app-parent',
template: `
<app-child [parentData]="parentData"></app-child>
`,
})
export class ParentComponent {
parentData = 'Data from parent';
}Child Component (child.component.ts):
import { Component, Input } from '@angular/core';
@Component({
selector: 'app-child',
template: `
<p>Received from parent: {{ parentData }}</p>
`,
})
export class ChildComponent {
@Input() parentData: string;
}
You can also use @ViewChild or @ContentChild decorators to access a child component or element directly in the parent component and set its properties or invoke its methods.
Parent Component (parent.component.ts):
import { Component, AfterViewInit, ViewChild } from '@angular/core';
import { ChildComponent } from './child.component';
@Component({
selector: 'app-parent',
template: `
<app-child></app-child>
`,
})
export class ParentComponent implements AfterViewInit {
@ViewChild(ChildComponent) child: ChildComponent;
ngAfterViewInit() {
this.child.childData = 'Data from parent'; // Set data in child component
}
}
Child Component (child.component.ts):
import { Component } from '@angular/core';
@Component({
selector: 'app-child',
template: `
<p>Received from parent: {{ childData }}</p>
`,
})
export class ChildComponent {
childData: string;
}
15. How do you emit data from a child component to a parent component?
Answer: You can use Output properties along with EventEmitter to emit events from a child component to a parent component.
Child Component (child.component.ts):
import { Component, EventEmitter, Output } from '@angular/core';
@Component({
selector: 'app-child',
template: `
<button (click)="emitData()">Emit Data</button>
`,
})
export class ChildComponent {
@Output() dataEmitter = new EventEmitter<string>();
emitData() {
const data = 'Data from child';
this.dataEmitter.emit(data); // Emit the data
}
}
Parent Component (parent.component.ts):
import { Component } from '@angular/core';
@Component({
selector: 'app-parent',
template: `
<app-child (dataEmitter)="receiveData($event)"></app-child>
<p>Received in parent: {{ receivedData }}</p>
`,
})
export class ParentComponent {
receivedData: string;
receiveData(data: string) {
this.receivedData = data; // Assign the received data
}
}
16. What is ng-content used for?
Answer: ng-content is used to project content from a parent component into the child component's template.
Parent Component (parent.component.html):
import { Component } from '@angular/core';
@Component({
selector: 'app-parent',
template: `
<div class="parent">
<h2>Parent Component</h2>
<app-child>
<p>This is content projected into the child component.</p>
</app-child>
</div>
`,
})
export class ParentComponent {}
Child Component (child.component.html):
import { Component } from '@angular/core';
@Component({
selector: 'app-child',
template: `
<div class="child">
<h3>Child Component</h3>
<ng-content></ng-content> <!-- Content from parent will be projected here -->
</div>
`,
})
export class ChildComponent {}
17. What is View Encapsulation in Angular?
Answer: View Encapsulation is a feature in Angular that allows you to control the scope and styling of CSS for a component and its template.
18. What is decorator?.
Answer: A decorator is a special kind of function that is used to modify classes, methods, properties, or parameters.
Some commonly used decorators are:
(a). @Component: This decorator is used to define an Angular component. It provides metadata about the component, such as its selector, template, styles, and more.
import { Component } from '@angular/core';
@Component({
selector: 'app-example',
template: '<p>This is an example component.</p>',
})
export class ExampleComponent {}
(b). @Directive: This decorator is used to define a custom directive in Angular. Directives are used to add behavior or modify the DOM within templates.
import { Directive, ElementRef, HostListener } from '@angular/core';
@Directive({
selector: '[appHighlight]'
})
export class HighlightDirective {
constructor(private el: ElementRef) {}
@HostListener('mouseenter') onMouseEnter() {
this.highlight('yellow');
}
@HostListener('mouseleave') onMouseLeave() {
this.highlight(null);
}
private highlight(color: string | null) {
this.el.nativeElement.style.backgroundColor = color;
}
}
(c). @Injectable: This decorator is used to annotate a class as an injectable service. Services are a fundamental part of Angular and are used for sharing data and functionality across components and other parts of the application.
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root'
})
export class DataService {
// Service logic here
}
(d). @Input and @Output: These decorators are used within component classes to define input properties and output events, respectively. They allow data to flow into and out of components.
import { Component, Input, Output, EventEmitter } from '@angular/core';
@Component({
selector: 'app-child',
template: '<button (click)="sendMessage()">Send Message</button>'
})
export class ChildComponent {
@Input() message: string;
@Output() messageSent = new EventEmitter<string>();
sendMessage() {
this.messageSent.emit(this.message);
}
}
(e). @NgModule: This decorator is used to define Angular modules. Modules are used to organize the application and group related components, services, and directives.
import { NgModule } from '@angular/core';
@NgModule({
declarations: [AppComponent, HeaderComponent, FooterComponent],
imports: [BrowserModule, HttpClientModule],
providers: [DataService],
bootstrap: [AppComponent]
})
export class AppModule {}19. What are template-driven forms in Angular?
Answer: Template-driven forms are forms where form controls are bound directly to elements in the template using ngModel. ngForm directive is used to create and manage template-driven forms.
<form #myForm="ngForm" (ngSubmit)="onSubmit(myForm.value)">
<div class="form-group">
<label for="name">Name:</label>
<input type="text" id="name" name="name" ngModel required>
</div>
<div class="form-group">
<label for="email">Email:</label>
<input type="email" id="email" name="email" ngModel required email>
</div>
<button type="submit">Submit</button>
</form>
20. What are reactive forms in Angular?
Answer: Reactive forms are forms where form controls are created programmatically and synchronized with the template using data binding.
import { Component } from '@angular/core';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
@Component({
selector: 'app-registration',
template: `
<form [formGroup]="registrationForm" (ngSubmit)="onSubmit()">
<div class="form-group">
<label for="name">Name:</label>
<input type="text" id="name" formControlName="name">
</div>
<div class="form-group">
<label for="email">Email:</label>
<input type="email" id="email" formControlName="email">
</div>
<button type="submit" [disabled]="!registrationForm.valid">Submit</button>
</form>
`,
})
export class RegistrationComponent {
registrationForm: FormGroup;
constructor(private fb: FormBuilder) {
this.registrationForm = this.fb.group({
name: ['', [Validators.required]],
email: ['', [Validators.required, Validators.email]],
});
}
onSubmit() {
// Handle form submission here
console.log(this.registrationForm.value);
}
}
21. Explain FormBuilder in Angular.
Answer: FormBuilder is a service provided by Angular that simplifies the process of creating and managing form controls in reactive forms.
22. What is the purpose of ngModelGroup in forms?
Answer: ngModelGroup is used to group form controls together for easier validation and manipulation.
23. What is RxJS?
Answer: RxJS (Reactive Extensions for JavaScript) is a library for handling asynchronous and event-based programming using observables.
24. What is an observable in Angular?
Answer: An observable is a data stream that represents a sequence of values or events that can occur over time. Observables are used for handling asynchronous operations, such as making HTTP requests.
import { Observable } from 'rxjs';
// Create an observable that emits values 1, 2, and 3 with a delay
const myObservable = new Observable<number>((observer) => {
observer.next(1);
setTimeout(() => {
observer.next(2);
}, 1000);
setTimeout(() => {
observer.next(3);
observer.complete(); // Indicates the observable has completed
}, 2000);
});
// Subscribe to the observable
const subscription = myObservable.subscribe({
next: (value) => console.log(`Received: ${value}`),
error: (error) => console.error(`Error: ${error}`),
complete: () => console.log('Observable complete'),
});
// Unsubscribe when no longer needed (to prevent memory leaks)
subscription.unsubscribe();
25. How do you create an observable in Angular?
Answer: You can create an observable using the Observable.create() method or by using operators like from, of, or interval.
26. Explain the concept of operators in RxJS.
Answer: Operators are functions used to manipulate and transform observables. Examples include map, filter, mergeMap, etc.
27. How do you make HTTP requests in Angular?
Answer: The HttpClient module is used to make HTTP requests. It provides methods for GET, POST, PUT, DELETE, and other HTTP operations.
28. What is an HTTP interceptor in Angular?
Answer: An HTTP interceptor is a middleware that intercepts HTTP requests and responses, allowing you to modify them before they are sent or after they are received.
29. How do you handle errors in Angular HTTP requests?
Answer: You can handle errors using the catchError operator in RxJS. Additionally, you can use the subscribe method's error callback.
30. What is the purpose of the async pipe?
Answer: The async pipe is used in templates to automatically subscribe to an observable and update the template whenever the observable emits new values.
31. What are pipes in Angular?
Answer: Pipes are used to transform and format data in templates. They can be used for filtering, sorting, and formatting.
32. Give examples of built-in pipes in Angular.
Answer: Examples of built-in pipes include date, uppercase, lowercase, currency, and json.
33. How do you create a custom pipe in Angular?
Answer: You can create a custom pipe by implementing the PipeTransform interface and providing the transform method.
34. What is NgRx?
Answer: NgRx is a popular library for managing state in Angular applications using the Redux pattern.
35. What is the Redux pattern?
Answer: The Redux pattern is a design pattern for managing the state of a web application in a predictable and centralized manner. In this pattern, the entire application state is stored in a single object called the "store." This store acts as the single source of truth for the application's data.
36. What are actions, reducers, and selectors in NgRx?
Answer: Actions represent events that can change the state, reducers handle those events and modify the state, and selectors extract specific pieces of state data.
37. What is Angular Universal?
Answer: Angular Universal is a framework that allows you to run Angular applications on the server side. This means that pages can be rendered on the server and sent as fully-rendered HTML to the client, improving initial page load performance and SEO. This approach is often referred to as server-side rendering (SSR) or universal rendering.
38. What are different lifecycle hooks in Angular?
Answer: Lifecycle hooks provide the ability to execute custom logic at specific moments during the creation, update, and destruction of Angular components.
(a). ngOnChanges: This hook is called whenever the input properties of a component change. It receives an object containing the previous and current values of the input properties.
(b). ngOnInit: This hook is called once after the component is initialized. It's a good place to put initialization logic for your component, such as fetching data from a server.
(c). ngDoCheck: This hook is called during every change detection cycle. It allows you to implement custom change detection logic. Use it with caution, as it can impact performance.
(d). ngAfterContentInit: This hook is called once after Angular projects external content (such as content passed into a component through <ng-content>).
(e). ngAfterContentChecked: This hook is called after every check of a component's content. It allows you to react to changes in the content projection.
(f). ngAfterViewInit: This hook is called once after the component's view is initialized. It's often used for DOM manipulation or working with child components.
(g). ngAfterViewChecked: This hook is called after every check of the component's view. Like ngAfterContentChecked, it's useful for reacting to changes in the view.
(h). ngOnDestroy: This hook is called just before a component is destroyed. It provides an opportunity to clean up resources, unsubscribe from observables, or perform other cleanup tasks to prevent memory leaks.
import { Component, Input, OnChanges, OnInit, OnDestroy } from '@angular/core';
@Component({
selector: 'app-lifecycle-example',
template: '<p>{{ message }}</p>',
})
export class LifecycleExampleComponent implements OnChanges, OnInit, OnDestroy {
@Input() data: string;
message: string;
ngOnChanges(changes: SimpleChanges): void {
if (changes.data) {
this.message = `Data changed from '${changes.data.previousValue}' to '${changes.data.currentValue}'`;
}
}
ngOnInit(): void {
// Initialization logic, data fetching, etc.
}
ngOnDestroy(): void {
// Cleanup tasks, such as unsubscribing from observables.
}
}
39. What is the purpose of the @HostListener decorator in Angular?
Answer: @HostListener is used to listen to events on the host element of a directive and trigger a method when the event occurs.
import { Component, HostListener } from '@angular/core';
@Component({
selector: 'app-host-listener-example',
template: '<div (click)="toggle()">Click me</div>',
})
export class HostListenerExampleComponent {
isClicked = false;
@HostListener('click', ['$event'])
toggle(event: MouseEvent) {
this.isClicked = !this.isClicked;
console.log(`Element clicked at (${event.clientX}, ${event.clientY})`);
}
}40. What is AOT compilation in Angular?
Answer: AOT (Ahead-of-Time) compilation refers to the process of compiling your Angular application's TypeScript code and templates into efficient JavaScript during build time. It helps optimize performance and reduce the size of your application bundle.
41. What is JIT compilation in Angular?
Answer: JIT (Just-in-Time) compilation refers to the process of compiling your Angular application's TypeScript code and templates into JavaScript code at runtime, inside the user's web browser. JIT compilation is convenient during development.
42. Explain Angular's ngZone.
Answer: NgZone (short for "Angular Zone") is a core part of the Angular framework that helps manage and handle asynchronous operations and change detection. Angular uses the Zone.js library to create and manage zones.
Zones are execution contexts that can track asynchronous tasks. NgZone creates a default zone for your application. When you run code within this zone, Angular is aware of it and can trigger change detection appropriately.
NgZone is particularly helpful when dealing with third-party libraries or APIs that are not Zone.js-aware.
NgZone is particularly helpful when dealing with third-party libraries or APIs that are not Zone.js-aware.
43. What are Angular guards, and how are they used?
Answer: Angular guards are used to control navigation and access to routes. There are different types of guards, such as CanActivate, CanDeactivate, CanLoad, and CanActivateChild, which allow you to add logic to protect routes.
44. Explain the purpose of the ActivatedRoute and Router in Angular.
Answer: ActivatedRoute provides information about the current route, while Router is used for programmatic navigation and route handling in Angular applications.
45. What is Angular's providedIn property in a service decorator used for?
Answer: The providedIn property specifies where the service should be provided. It can be set to 'root' to make it a singleton service available throughout the application. If you don't set providedIn, Angular creates a separate instance of the service for each component that requests it.
46. Explain Angular's ViewChild and ViewChildren decorators.
Answer: ViewChild and ViewChildren are decorators used to access and manipulate child components, DOM elements, or directives from a parent component. These decorators provide a way to establish a connection between the parent component and its child elements or components, allowing the parent to interact with or retrieve data from them.
ViewChild: The @ViewChild decorator allows a parent component to access a single child component, element, or directive that matches a specific selector defined in the template.
It is used to obtain a reference to the first matching child element or component.
The child element or component is selected using a CSS selector.
It is used to obtain a reference to the first matching child element or component.
The child element or component is selected using a CSS selector.
You can use the static property of @ViewChild to specify whether the query should be static (resolved at compile time) or dynamic (resolved at runtime). The default is dynamic.
It returns a reference to the child component, which can then be used to call methods or access properties of the child.
import { Component, ViewChild, ElementRef } from '@angular/core';
@Component({
selector: 'app-parent',
template: '<app-child #myChild></app-child>'
})
export class ParentComponent {
@ViewChild('myChild') child: ElementRef;
ngAfterViewInit() {
// Access the child element
console.log(this.child.nativeElement);
}
}ViewChildren: The @ViewChildren decorator is similar to @ViewChild, but it allows you to query and obtain references to multiple child components, elements, or directives that match a specified selector.
It returns a QueryList, which is a collection of matched child elements or components.
Like @ViewChild, you can use the static property to specify whether the query should be static or dynamic.
import { Component, ViewChildren, QueryList, ElementRef } from '@angular/core';
@Component({
selector: 'app-parent',
template: '<app-child *ngFor="let item of items" #myChild></app-child>'
})
export class ParentComponent {
@ViewChildren('myChild') children: QueryList<ElementRef>;
items = [1, 2, 3];
ngAfterViewInit() {
// Access multiple child elements
this.children.forEach(child => console.log(child.nativeElement));
}
}47. What is Tree-Shaking.
Answer: Tree-Shaking refers to the process of eliminating unused code or "dead code" from your JavaScript bundles to reduce their size and improve application performance. It relies on the import and export statements to detect if code modules are exported and imported for use between JavaScript files.
Angular applications are often built using the Webpack build tool, which has built-in support for tree shaking. Webpack analyzes the import statements in your code and figures out which parts of your codebase are actually used. Any code that is not imported or used in your application is considered dead code.
48. Explain the difference between Shallow Copy vs Deep Copy.
Answer: A shallow copy(Copy by Reference) is an exact copy of the source object whose properties share the same references(memory address). while In deep copy(Copy by Value) an object is copied along with its values. There is no sharing of references between the source and deep-copied objects.
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