Top Angular Interview Questions (2025)

Question: How does Angular handle routing? What is the role of RouterModule?

Answer:

Routing in Angular allows you to navigate between different views or components in a single-page application (SPA). Angular provides a robust routing mechanism that enables developers to define how users navigate between different views or pages of the application.

The RouterModule is a core part of Angular’s routing system, providing all the tools necessary for routing management, including defining routes, navigating between components, and handling route parameters, lazy loading, and other advanced routing features.

---

How Angular Handles Routing:

Angular’s routing system is based on the concept of routes, where each route associates a path with a component. When a user navigates to a specific URL, Angular’s router loads the corresponding component to display the appropriate view.

The key components of Angular’s routing system are:

1. RouterModule:

   • The RouterModule is the core module that contains all the routing-related functionality in Angular.
   • It is responsible for configuring routes, managing navigation, and handling route guards, lazy loading, and other features.

2. Routes:

   • Routes are a collection of path-component pairs, which define the mapping between a URL path and the component to display for that path.

3. RouterOutlet:

   • The RouterOutlet is a directive where the routed components are displayed. It acts as a placeholder in the template to render the matched component.

4. RouterLink:

   • The RouterLink directive is used to navigate between routes. It is typically applied to anchor (<a>) tags or other clickable elements to bind them to a specific route path.

5. Router Service:

   • The Router service is used for programmatic navigation, handling things like redirects or navigation based on user actions.

---

Role of RouterModule:

The RouterModule is an Angular module that provides the necessary services, directives, and components for routing within an Angular application. It needs to be imported in the root or feature module to enable routing functionality.

Key Features of RouterModule:

1. Defining Routes:

   • The RouterModule provides the RouterModule.forRoot() method for configuring routes in the root module and RouterModule.forChild() for feature modules. This is where you define the paths and associated components for navigation.

2. Navigating Between Views:

   • It enables navigation between views (components) based on URL changes through the browser. When the user clicks a link or a route is activated, the Router updates the view without reloading the entire page, maintaining the SPA behavior.

3. Route Guards:

   • The RouterModule supports route guards such as CanActivate, CanDeactivate, and Resolve. These guards allow you to control access to routes or perform actions before a route is activated.

4. Lazy Loading:

   • The RouterModule supports lazy loading of feature modules, meaning that certain parts of the application (feature modules) are only loaded when required, improving performance by reducing the initial load time.

5. Handling Parameters:

   • The router allows you to pass dynamic parameters in the URL (e.g., /user/123) and retrieve them inside the component using route parameter observables.

6. Query Parameters:

   • Query parameters, which are added after the ? symbol in a URL (e.g., /search?term=angular), can be used to pass optional parameters to routes. The Router provides an easy API to read query parameters.

---

Steps to Set Up Routing in Angular:

Here’s a breakdown of how routing is typically set up in Angular:

1. Step 1: Import RouterModule in AppModule: The RouterModule is imported into the root module (app.module.ts) using RouterModule.forRoot(routes), where routes is an array of route definitions.

   import { NgModule } from '@angular/core';
   import { BrowserModule } from '@angular/platform-browser';
   import { RouterModule, Routes } from '@angular/router';
   import { AppComponent } from './app.component';
   import { HomeComponent } from './home/home.component';
   import { AboutComponent } from './about/about.component';
   
   const routes: Routes = [
     { path: '', component: HomeComponent },
     { path: 'about', component: AboutComponent },
   ];
   
   @NgModule({
     declarations: [
       AppComponent,
       HomeComponent,
       AboutComponent
     ],
     imports: [
       BrowserModule,
       RouterModule.forRoot(routes) // Set up routes
     ],
     providers: [],
     bootstrap: [AppComponent]
   })
   export class AppModule { }

2. Step 2: Add RouterOutlet in the Template: The RouterOutlet directive is added to the root component template (app.component.html) as a placeholder for the routed views.

   <nav>
     <a routerLink="/">Home</a>
     <a routerLink="/about">About</a>
   </nav>
   
   <router-outlet></router-outlet> <!-- Placeholder for routed component -->

3. Step 3: Use RouterLink for Navigation: To navigate between routes, use the routerLink directive on anchor tags or any other clickable element. This tells Angular to update the view when the user clicks the link.

   <a routerLink="/about">About Us</a>

4. Step 4: Use Router Service for Programmatic Navigation: You can navigate programmatically using the Router service inside your component class.

   import { Component } from '@angular/core';
   import { Router } from '@angular/router';
   
   @Component({
     selector: 'app-home',
     templateUrl: './home.component.html',
   })
   export class HomeComponent {
   
     constructor(private router: Router) {}
   
     navigateToAbout() {
       this.router.navigate(['/about']);
     }
   }

---

Advanced Routing Features:

1. Route Parameters: Routes can accept dynamic parameters, which are passed in the URL. These parameters can be accessed using Angular’s ActivatedRoute.

   Example:

   const routes: Routes = [
     { path: 'user/:id', component: UserComponent },
   ];

   Accessing the route parameter in the component:

   import { ActivatedRoute } from '@angular/router';
   
   export class UserComponent {
     constructor(private route: ActivatedRoute) {}
   
     ngOnInit() {
       const userId = this.route.snapshot.paramMap.get('id');
       console.log(userId); // Output: value of 'id' parameter
     }
   }

2. Lazy Loading: Angular supports lazy loading for feature modules, meaning that modules are loaded only when they are needed, rather than during the initial load of the application.

   Example:

   const routes: Routes = [
     { path: 'dashboard', loadChildren: () => import('./dashboard/dashboard.module').then(m => m.DashboardModule) },
   ];

3. Route Guards: Route guards like CanActivate, CanDeactivate, and Resolve allow you to control navigation based on conditions. These guards can prevent unauthorized users from accessing routes or perform tasks before navigating.

   Example (CanActivate):

   import { CanActivate } from '@angular/router';
   
   export class AuthGuard implements CanActivate {
     canActivate() {
       return this.authService.isAuthenticated(); // Check if the user is authenticated
     }
   }

---

Conclusion:

Angular handles routing through the RouterModule, which enables developers to define paths, map them to components, and manage navigation between views in a single-page application. The RouterModule provides a powerful, flexible, and declarative way to manage routes, including features like dynamic parameters, lazy loading, route guards, and programmatic navigation. By setting up routes and using RouterOutlet and RouterLink, developers can create seamless navigation experiences within Angular applications.

Question: What are Angular services and how are they different from components?

Answer:

Angular Services and Components are both fundamental building blocks in Angular applications, but they serve distinct purposes and have different roles in the application architecture.

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What are Angular Services?

In Angular, a service is a class that provides specific functionality and business logic that can be shared across multiple components. Services are used to organize and share data, manage state, and perform tasks such as HTTP requests, data storage, logging, etc. They are typically designed to be injected into components or other services via Angular’s Dependency Injection (DI) system.

Key Characteristics of Services:

1. Encapsulation of Logic: Services encapsulate specific functionality that doesn’t belong to a component’s UI logic, such as data fetching, handling business rules, or managing state. For example, a service might handle HTTP requests to an API and return the response to the component.

2. Reusability: Since services are typically injected into multiple components or other services, they provide a way to avoid code duplication and enable reusable logic across the application.

3. Singleton: By default, services in Angular are singleton objects when provided in the root module or component. This means that the same instance of the service is shared across the entire application, or a specific module/component if provided at that scope.

4. No View: Services do not have a view or template. They are simply classes with methods that encapsulate logic and can be used by other parts of the application.

5. Dependency Injection (DI): Angular uses DI to provide instances of services to components and other services. Services can be injected through the constructor of a component or another service.

Example of a Service:

import { Injectable } from '@angular/core';
import { HttpClient } from '@angular/common/http';
import { Observable } from 'rxjs';

@Injectable({
  providedIn: 'root', // Service is available globally
})
export class DataService {
  constructor(private http: HttpClient) {}

  getData(): Observable<any> {
    return this.http.get('https://api.example.com/data');
  }
}

Using the Service in a Component:

import { Component, OnInit } from '@angular/core';
import { DataService } from './data.service';

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
})
export class MyComponent implements OnInit {
  data: any;

  constructor(private dataService: DataService) {}

  ngOnInit(): void {
    this.dataService.getData().subscribe(response => {
      this.data = response;
    });
  }
}

---

What are Angular Components?

Components in Angular are the building blocks of the UI (user interface) of an Angular application. A component controls a part of the screen (a view), is responsible for rendering the view, and managing the behavior associated with that view. Each component in Angular has its own template (HTML), style (CSS/SCSS), and a class that defines the logic for that component.

Key Characteristics of Components:

1. View: Components are associated with a view (HTML template) that is rendered in the browser. The template defines the structure and layout of the component’s UI.

2. UI Logic: Components handle the UI-related logic. This includes handling user interactions (like button clicks, form submissions), responding to events, and updating the view.

3. Encapsulation: Components encapsulate their view and behavior. This allows for reusable and self-contained building blocks of the UI.

4. Dependency Injection: Like services, components can also use DI to inject services into their constructor to get access to shared functionality (e.g., data services).

5. Component Lifecycle: Components have a lifecycle with various hooks like ngOnInit(), ngOnChanges(), and ngOnDestroy() to respond to changes and lifecycle events.

Example of a Component:

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

@Component({
  selector: 'app-my-component',
  templateUrl: './my-component.component.html',
  styleUrls: ['./my-component.component.css']
})
export class MyComponent implements OnInit {
  title: string = 'Hello, Angular!';

  constructor() {}

  ngOnInit(): void {
    console.log('Component initialized');
  }
}

Template for the Component (my-component.component.html):

<h1>{{ title }}</h1>
<button (click)="changeTitle()">Change Title</button>

---

Differences Between Services and Components

Aspect	Service	Component
Purpose	Provides shared logic, data, and functionality across components.	Controls a part of the UI and manages its view and behavior.
View	No view or template. Only logic and data.	Has a view (HTML template) and handles UI logic.
Injection	Services are injected into components or other services using DI.	Components are generally not injected; they are declared in the module’s declarations array.
Lifecycle Hooks	No lifecycle hooks specific to services (but can have custom logic for initialization).	Has lifecycle hooks such as ngOnInit, ngOnDestroy, ngOnChanges, etc.
Reusability	Services are highly reusable and can be used across multiple components or modules.	Components are specific to a part of the UI and usually interact with one another.
Singleton	Services are often singleton instances (shared across the app or module).	Each component has its own instance.
State Management	Services are often used for state management or sharing data between components.	Components manage their own internal state (although state can be shared via services).
Communication	Services are used to manage communication between components (e.g., shared data, event handling).	Components handle communication with the user and other components (through event bindings and services).

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Conclusion:

• Services are Angular classes used to manage and share data and business logic across components. They do not have a view and are typically used for tasks like HTTP requests, data storage, or encapsulating complex logic.

• Components are the UI building blocks of Angular applications. They are responsible for rendering views and managing UI-related logic. Each component has a template (HTML), styles, and a class that defines its behavior.

While components are focused on the user interface and interaction, services are focused on providing reusable, sharable logic and data across the application. The two work together, with components using services to access shared functionality and data.

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