Angular Interview Questions And Answer for beginner part -1
When preparing for an Angular interview, it’s important to be well-versed in various aspects of the framework. Angular is a powerful and widely-used front-end web development framework maintained by Google. It’s known for its robust features, two-way data binding, modular architecture, and extensive set of tools and libraries. Here’s a brief introduction to set the stage for Angular interview questions:
Question 1:
What is Angular and how is it different from AngularJS?
Answer :
Angular is a TypeScript-based open-source web application framework developed by Google. It’s a complete rewrite of AngularJS, addressing its limitations. Angular uses a component-based architecture, provides two-way data binding, and has a powerful dependency injection system. The major difference is that AngularJS is based on JavaScript, while Angular is built with TypeScript, offering enhanced maintainability, scalability, and tooling support.
Question 2:
Explain the Angular Component Lifecycle Hooks.
Answer :
Angular components have a lifecycle that goes through various phases. Some notable hooks include ngOnInit, ngOnChanges, and ngOnDestroy. For example, ngOnInit is used to perform initialization tasks when a component is created. Understanding these hooks is crucial for managing component behavior during its lifecycle.
Question 3:
What is the difference between ngIf and ngFor in Angular?
Answer :
ngIf is a structural directive that conditionally adds or removes elements from the DOM based on a given expression. On the other hand, ngFor is used for iterating over a collection and rendering elements accordingly. For instance, ngIf can be employed to conditionally display a component, while ngFor can loop through an array to render multiple components.
Question 4:
What is Angular CLI, and how does it simplify the development process?
Answer :
Angular CLI (Command Line Interface) is a powerful tool that simplifies the creation, configuration, and deployment of Angular applications. Developers can use commands like ng new to generate a new project, ng generate to create components, services, etc., and ng build to compile and bundle the application for deployment. It streamlines the development process by automating common tasks and providing a consistent project structure.
Question 5:
Explain the concept of Angular Modules.
Answer :
Angular Modules are containers for organizing and managing components, directives, services, and other pieces of an Angular application. They use the @NgModule decorator. Modules help in organizing code, separating concerns, and enabling lazy loading for efficient application loading. For instance, a module can encapsulate related features, making it easier to maintain and scale the application.
Question 6:
What is Dependency Injection in Angular? Provide an example.
Answer :
Dependency Injection (DI) is a design pattern in which components receive their dependencies from an external source, rather than creating them internally. Angular’s DI system is used to inject services into components. For example, consider a service named DataService:
// DataService example
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root',
})
export class DataService {
getData(): string {
return 'Angular Dependency Injection Example';
}
}Now, a component can inject this service:
// Component example
import { Component } from '@angular/core';
import { DataService } from './data.service';
@Component({
selector: 'app-example',
template: '{{ message }}',
})
export class ExampleComponent {
message: string;
constructor(private dataService: DataService) {
this.message = dataService.getData();
}
}Here, DataService is injected into ExampleComponent.
Question 7:
What is Two-Way Data Binding in Angular? Provide an example.
Answer :
Two-Way Data Binding is a feature in Angular that allows automatic synchronization between the model and the view. The ngModel directive is commonly used for two-way data binding. For example, consider a simple input field:
<!-- Two-Way Data Binding Example -->
<input [(ngModel)]="name" />
<p>{{ name }}</p>In this example, the input field is bound to the name property using [(ngModel)]. Any changes to the input will automatically update the name property, and vice versa.
Question 8:
Explain Angular Routing and provide an example.
Answer :
Angular Routing is a mechanism for navigating between different components (views) in a single-page application. The RouterModule is used to configure routes. For example:
// app-routing.module.ts
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 {}- Now, in the main
app.module.ts:
// app.module.ts
import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { AppRoutingModule } from './app-routing.module';
import { HomeComponent } from './home/home.component';
import { AboutComponent } from './about/about.component';
@NgModule({
declarations: [HomeComponent, AboutComponent],
imports: [BrowserModule, AppRoutingModule],
bootstrap: [AppComponent],
})
export class AppModule {}And in the template:
<!-- app.component.html -->
<router-outlet></router-outlet>Now, navigating to / will display the HomeComponent, and navigating to /about will display the AboutComponent.
Question 9:
How do you handle HTTP requests in Angular? Provide an example using HttpClient.
Answer :
Angular provides the HttpClient module for making HTTP requests. For example:
// data.service.ts
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
@Injectable({
providedIn: 'root',
})
export class DataService {
private apiUrl = 'https://api.example.com/data';
constructor(private http: HttpClient) {}
getData(): Observable<any> {
return this.http.get(this.apiUrl);
}
}Now, a component can use this service to fetch data:
// component.ts
import { Component, OnInit } from '@angular/core';
import { DataService } from './data.service';
@Component({
selector: 'app-example',
template: '{{ data | json }}',
})
export class ExampleComponent implements OnInit {
data: any;
constructor(private dataService: DataService) {}
ngOnInit() {
this.dataService.getData().subscribe((result) => {
this.data = result;
});
}
}In this example, the DataService is used to fetch data from an API using HttpClient.
Question 10:
What are Angular Pipes? Provide an example.
Answer :
Angular Pipes are used for transforming and formatting data in the template. For example:
// component.ts
import { Component } from '@angular/core';
@Component({
selector: 'app-example',
template: '<p>{{ today | date: "short" }}</p>',
})
export class ExampleComponent {
today: Date = new Date();Question 11:
Explain Angular Services and their use cases. Provide an example.
Answer :
Angular services are singleton objects that can be injected into components and other services to encapsulate and share logic. They are often used for communication with servers, state management, and other business logic. For example:
// data.service.ts
import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';
@Injectable({
providedIn: 'root',
})
export class DataService {
private apiUrl = 'https://api.example.com/data';
constructor(private http: HttpClient) {}
getData(): Observable<any> {
return this.http.get(this.apiUrl);
}
}In this example, DataService encapsulates the logic for fetching data from an API. It can be injected into multiple components, ensuring a single instance of the service is shared across the application.
Question 12:
Explain Angular Reactive Forms. Provide an example.
Answer :
Reactive Forms in Angular provide a model-driven approach to handling forms and their validation. Developers define the form structure and behavior in the component class. For example:
// component.ts
import { Component } from '@angular/core';
import { FormBuilder, FormGroup, Validators } from '@angular/forms';
@Component({
selector: 'app-example',
template: `
<form [formGroup]="myForm" (ngSubmit)="onSubmit()">
<input formControlName="username" />
<button type="submit">Submit</button>
</form>
`,
})
export class ExampleComponent {
myForm: FormGroup;
constructor(private fb: FormBuilder) {
this.myForm = this.fb.group({
username: ['', Validators.required],
});
}
onSubmit() {
console.log('Form submitted:', this.myForm.value);
}
}In this example, the FormBuilder is used to create a reactive form with a validation rule for the username field. The form data is bound to the component, and the onSubmit method handles form submission.
Question 13:
What is Angular Directives? Provide examples of built-in and custom directives.
Answer :
Angular directives are markers on a DOM element that tell Angular to do something to that element. Built-in directives include ngIf, ngFor, and ngSwitch. For example:
<!-- Built-in Directives Example -->
<div *ngIf="showElement">This will only be shown if showElement is true.</div>
<ul>
<li *ngFor="let item of items">{{ item }}</li>
</ul>Additionally, you can create custom directives. For example, a directive to highlight an element:
// highlight.directive.ts
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) {
this.el.nativeElement.style.backgroundColor = color;
}
}Now, you can use this custom directive in your template:
<!-- Custom Directive Example -->
<p appHighlight>Hover over me to see the highlight effect!</p>This custom directive will highlight the background of the element when the mouse enters and remove the highlight when it leaves.
Question 14:
Explain Angular NgRx and its use in state management. Provide an example.
Answer :
NgRx is a state management library for Angular applications inspired by Redux. It helps manage the state of an application in a predictable way. For example:
// app.state.ts
import { createAction, createReducer, on, createSelector } from '@ngrx/store';
export const increment = createAction('Increment');
export const decrement = createAction('Decrement');
export const reset = createAction('Reset');
export interface AppState {
counter: number;
}
export const initialState: AppState = {
counter: 0,
};
export const counterReducer = createReducer(
initialState,
on(increment, (state) => ({ ...state, counter: state.counter + 1 })),
on(decrement, (state) => ({ ...state, counter: state.counter - 1 })),
on(reset, (state) => initialState)
);
export const selectCounter = (state: AppState) => state.counter;
export const selectCounterDoubled = createSelector(selectCounter, (counter) => counter * 2);In this example, actions (increment, decrement, reset) and a reducer (counterReducer) are defined. NgRx store helps manage the state changes triggered by these actions. Selectors (selectCounter, selectCounterDoubled) are used to derive specific pieces of state. This state management pattern enhances predictability and maintainability in large applications.
Question 15:
What are Angular Guards and how are they used in routing? Provide an example.
Answer :
Angular Guards are used to control navigation and access to routes. They can be used to perform checks before allowing navigation to occur. For example:
// auth.guard.ts
import { Injectable } from '@angular/core';
import { CanActivate, ActivatedRouteSnapshot, RouterStateSnapshot, Router } from '@angular/router';
@Injectable({
providedIn: 'root',
})
export class AuthGuard implements CanActivate {
constructor(private router: Router) {}
canActivate(
next: ActivatedRouteSnapshot,
state: RouterStateSnapshot
): boolean {
// Check if the user is authenticated
const isAuthenticated = /* Logic to check authentication status */;
if (isAuthenticated) {
return true;
} else {
// Redirect to the login page
this.router.navigate(['/login']);
return false;
}
}
}Now, you can use this guard in your route configuration:
// app-routing.module.ts
import { AuthGuard } from './auth.guard';
const routes: Routes = [
{ path: 'dashboard', component: DashboardComponent, canActivate: [AuthGuard] },
// Other routes...
];In this example, the AuthGuard is applied to the dashboard route, ensuring that only authenticated users can access it.
Question 16:
Explain Angular Dependency Injection Hierarchical Injector. Provide an example.
Answer :
Angular’s dependency injection system supports a hierarchical injector. This means that each component has its own injector, and they form a tree-like structure. For example:
// parent.service.ts
import { Injectable } from '@angular/core';
@Injectable({
providedIn: 'root',
})
export class ParentService {
value = 'Value from ParentService';
}// child.component.ts
import { Component } from '@angular/core';
import { ParentService } from './parent.service';
@Component({
selector: 'app-child',
template: '<p>{{ parentServiceValue }}</p>',
providers: [ParentService], // This creates a new instance of ParentService for this component and its children.
})
export class ChildComponent {
constructor(public parentServiceValue: ParentService) {}
}In this example, ChildComponent has its own instance of ParentService, and it overrides the service provided in the root injector. This hierarchical nature allows components to have their own services while still inheriting from higher-level injectors.
Conclusion :
In summary, Angular stands out as a robust and feature-rich front-end framework for building dynamic web applications. Its component-based architecture, TypeScript support, and powerful tools like Angular CLI make development efficient and maintainable. With features like two-way data binding, dependency injection, and advanced concepts like lazy loading and NgRx, Angular addresses the needs of complex applications. Developers can optimize performance through AOT compilation and change detection strategies. Overall, Angular’s versatility and strong community support position it as a leading choice for modern web development.
