Top 20 Angular Interview Questions and Answers with Code Examples
What is Angular?
Angular is a popular front-end web development framework that enables developers to build dynamic and interactive web applications using HTML, CSS, and JavaScript. It provides a range of powerful features, including data binding, dependency injection, and reusable components, that make it easier to develop and maintain complex web applications.
What is the difference between AngularJS and Angular?
AngularJS is an older version of the Angular framework, while Angular is the current version of the framework. Angular is a complete rewrite of AngularJS and provides many new features and improvements over the older version.
What is data binding in Angular?
Data binding is a core feature of Angular that enables the automatic synchronization of data between the component and the view. There are four types of data binding in Angular: Interpolation, Property Binding, Event Binding, and Two-Way Binding.
Example code for property binding:
What is dependency injection in Angular?
Dependency injection is a design pattern used in Angular to provide dependencies to components without requiring the components to create them themselves. This makes it easier to manage dependencies and allows for better testing of components.
Example code for dependency injection:
constructor(private http: HttpClient) { }
What is a directive in Angular?
A directive is a type of Angular component that provides additional functionality to HTML elements. Directives can be used to add behavior to existing HTML elements or to create new custom elements.
Example code for creating a custom directive:
import { Directive, ElementRef } from '@angular/core';
@Directive({
selector: '[appHighlight]'
})
export class HighlightDirective {
constructor(el: ElementRef) {
el.nativeElement.style.backgroundColor = 'yellow';
}
}
What is a service in Angular?
A service is a type of Angular component that provides functionality to other components. Services are used to encapsulate reusable code and to provide a single source of truth for data.
Example code for creating a service:
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
@Injectable({
providedIn: 'root'
})
export class DataService {
constructor(private http: HttpClient) { }
getData() {
return this.http.get('/api/data');
}
}
What is routing in Angular?
Routing is a feature of Angular that enables navigation between different components and views within an application. It is used to define the paths and URLs for different components and to handle navigation between them.
Example code for creating a routing module:
import { NgModule } from '@angular/core';
import { RouterModule, Routes } from '@angular/router';
import { HomeComponent } from './home/home.component';
import { AboutComponent } from './about/about.component';
const routes: Routes = [
{ path: '', component: HomeComponent },
{ path: 'about', component: AboutComponent },
];
@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }What is NgZone in Angular?
NgZone is a service provided by Angular that enables the monitoring and management of asynchronous operations in an application. It is used to detect and handle changes in the state of an application and to manage the performance of the application.
Example code for using NgZone:
import { Component, NgZone } from '@angular/core';
@Component({
selector: 'app-root',
template: `
`
})
export class AppComponent {
constructor(private zone: NgZone) { }
run() {
this.zone.runOutsideAngular(() => {
// Code to run outside the Angular zone
});
}
}
What is the difference between ngOnChanges and ngOnInit?
ngOnChanges is a lifecycle hook that is called when the value of a component’s input property changes. It receives an object containing the changes made to the input property. ngOnInit is a lifecycle hook that is called after the component’s input properties are initialized, and is used to perform any initialization logic required by the component.
Example code for using ngOnChanges:
import { Component, Input, OnChanges, SimpleChanges } from '@angular/core';
@Component({
selector: 'app-user',
template: `
{{ user.name }}
`
})
export class UserComponent implements OnChanges {
@Input() user: any;
ngOnChanges(changes: SimpleChanges) {
console.log('User input property changed:', changes.user.currentValue);
}
}
Example code for using ngOnInit:
import { Component, OnInit } from '@angular/core';
@Component({
selector: 'app-user',
template: `
{{ user.name }}
`
})
export class UserComponent implements OnInit {
user: any;
ngOnInit() {
this.user = { name: 'John Doe' };
}
}
What is NgIf in Angular?
NgIf is a built-in structural directive in Angular that conditionally adds or removes an element from the DOM based on a given condition.
Example code for using NgIf:
import { Component } from '@angular/core';
@Component({
selector: 'app-user',
template: `
Welcome, {{ username }}!
Please log in to continue.
`
})
export class UserComponent {
isLoggedIn = true;
username = 'John Doe';
}
What is a module in Angular?
A module is a logical container for a group of related components, directives, and services in an Angular application. Modules are used to organize the application into separate functional units, and to provide better separation of concerns.
Example code for creating a module:
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
@NgModule({
imports: [BrowserModule],
declarations: [AppComponent],
bootstrap: [AppComponent]
})
export class AppModule { }
What is the difference between a component and a directive in Angular?
A component is a type of directive that has its own template, and is used to create reusable UI elements in an Angular application. A directive, on the other hand, is a more general type of Angular construct that can be used to modify the behavior or appearance of existing HTML elements.
What is the purpose of the constructor in a component?
The constructor is a special method in a component that is called when the component is instantiated. It is used to initialize the component’s properties, and to inject any dependencies required by the component.
Example code for a component constructor:
import { Component, Inject } from '@angular/core';
import { DataService } from './data.service';
@Component({
selector: 'app-user',
template: `
Hello, {{ name }}!
`
})
export class UserComponent {
name: string;
constructor(private dataService: DataService) {
this.name = dataService.getUserName();
}
}
What is a service in Angular?
A service is a class in Angular that is used to provide functionality that can be shared across different parts of an application. Services are typically used to handle tasks such as data retrieval, authentication, and communication with external APIs.
Example code for creating a service:
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root'
})
export class DataService {
getUserName(): string {
return 'John Doe';
}
}
What is dependency injection in Angular?
Dependency injection is a design pattern used in Angular to provide components with the dependencies they need to perform their tasks. Dependencies are provided to a component through its constructor, and are typically implemented using services.
Example code for using dependency injection:
import { Component } from '@angular/core';
import { DataService } from './data.service';
@Component({
selector: 'app-user',
template: `
Hello, {{ name }}!
`
})
export class UserComponent {
name: string;
constructor(private dataService: DataService) {
this.name = dataService.getUserName();
}
}
What is a pipe in Angular?
A pipe is a built-in or custom function in Angular that is used to transform data before it is displayed in the UI. Pipes can be used for a variety of tasks, such as formatting dates, sorting arrays, and filtering lists.
Example code for using a built-in pipe:
import { Component } from '@angular/core';
@Component({
selector: 'app-user',
template: `
Joined: {{ joinDate | date }}
`
})
export class UserComponent {
joinDate = new Date();
}
What is a route guard in Angular?
A route guard is a service in Angular that is used to control access to a particular route in an application. Route guards are typically used to implement authentication and authorization logic.
Example code for using a route guard:
import { Injectable } from '@angular/core';
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot } from '@angular/router';
@Injectable({
providedIn: 'root'
})
export class AuthGuard implements CanActivate {
canActivate(route: ActivatedRouteSnapshot, state: RouterStateSnapshot): boolean {
// Check if the user is authenticated
if (isLoggedIn()) {
return true;
} else {
// Redirect to the login page
redirectToLogin();
return false;
}
}
}
What is the purpose of the NgModule decorator in Angular?
The NgModule decorator is used to define a module in an Angular application. It is used to configure the module’s imports, exports, providers, and declarations.
Example code for using the NgModule decorator:
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppComponent } from './app.component';
@NgModule({
imports: [BrowserModule],
declarations: [AppComponent],
bootstrap: [AppComponent]
})
export class AppModule { }
What is a reactive form in Angular?
A reactive form is a type of form in Angular that is created programmatically using a FormGroup object. Reactive forms provide more flexibility and control than template-driven forms, and are typically used for complex form scenarios.
Example code for creating a reactive form:
import { Component } from '@angular/core';
import { FormGroup, FormControl, Validators } from '@angular/forms';
@Component({
selector: 'app-contact',
template: `
`
})
export class ContactComponent {
contactForm = new FormGroup({
name: new FormControl('', Validators.required),
email: new FormControl('', [Validators.required, Validators.email])
});
onSubmit() {
// Submit the form
}
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Angular Interview Questions and Answers – Info Feather
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