Angular Services: A Comprehensive Guide

Introduction

Angular Services share data and functionality across components using singleton objects. They encapsulate business logic, thus enhancing code maintainability and reusability. We can inject services using the Angular dependency injection framework to create a modular and efficient framework.

Angular Services handles data processing, HTTP requests, and cross-component communication tasks. It works holistically to provide a streamlined application development environment.

Overview

Understanding in detail the importance of Angular Services and its characteristics will help better grasp the concept behind the seamless application development environment. The software services are essential because they encapsulate business logic, dependency injection, maintainability, and reusability, thus improving application efficiency. Angular makes it easy to factor our application logic into services. In Angular, dependency injection makes those services available to components.

In this article, we will discuss in detail the various aspects of Angular Services.

How to Create Service in Angular?

In this section, we will explain how to create services in Angular, the syntax for creating Services, the purpose of the @Injectable() decorator, and dependency injection.

The Syntax for Angular Creating a Service

We require the Angular CLI (Command Line Interface) before allowing the specific class syntax inside our service file.

1. Using Angular CLI to Generate a Service

Locate the Angular project directory and use the terminal or command prompt to execute the following code:

ng generate service my-service

Alternatively, we can use the shorthand version code as illustrated below.

ng g s my-service

The above code will create a service file (my-service.service.ts) inside the app folder alongside the accompanying testing file.

2. Service Class Syntax

The basic Angular service class syntax for the service file (my-service.service.ts) should look like the illustration below.

import { Injectable } from '@angular/core';

@Injectable({
providedIn: 'root' // This makes the service a singleton and available application-wide
})
export class MyServiceService {
constructor() { }

// Your service methods go here
}

Purpose of the @Injectable() Decorator

In the above example, the (@Injectable() decorator) indicates the class as one participating in the dependency injection system.

The (providedIn: 'root) tag is metadata denoting that the Angular DI system will have a single, shared instance of this service across the entire application.

The (export class MyServiceService { ... }) tag defines the class, where we can define methods and properties available to any class that injects this service.

Angular Services and Dependency Injection

We can utilize constructors of components or other services for injecting the Angular Services. Below is an illustration of how to use the (MyServiceService).

import { Component } from '@angular/core';
import { MyServiceService } from './my-service.service'; // Adjust the path as necessary

@Component({
selector: 'app-my-component',
templateUrl: './my-component.component.html',
styleUrls: ['./my-component.component.css']
})
export class MyComponent {
constructor(private myService: MyServiceService) {
// Now MyServiceService is available as this.myService within the component
}
}

Types of Angular Services

There are mainly two types of Angular Services. We can work with built-in or custom Angular services to develop web applications.

Built-in Angular Services

Built-in Angular Services include HttpClient, Router, AdvancedRoute, and FormBuilder services. Below is how we can use these built-in services.

a) HttpClient

The HttpClient built-in service is an efficient way to communicate with backend services over HTTP protocol. We can use it to type requests and responses, interception, request modification, progress events, or return RxJS Observables.

First import the import HttpClientModule.

import { NgModule } from '@angular/core';
import { BrowserModule } from '@angular/platform-browser';
import { HttpClientModule } from '@angular/common/http'; // Import HttpClientModule
import { AppComponent } from './app.component';

@NgModule({
declarations: [AppComponent],
imports: [
BrowserModule,
HttpClientModule // Import HttpClientModule here
],
providers: [],
bootstrap: [AppComponent]
})
export class AppModule { }

The second step is creating a service using the HttpClient as shown below.

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

@Injectable({
providedIn: 'root'
})
export class UserService {
private apiUrl = 'https://jsonplaceholder.typicode.com/users'; // Example API

constructor(private http: HttpClient) { }

getUsers(): Observable<any[]> {
return this.http.get<any[]>(this.apiUrl);
}
}

The last step is using the HttpClient service in a component as shown below.

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

@Injectable({
providedIn: 'root'
})
export class UserService {
private apiUrl = 'https://jsonplaceholder.typicode.com/users'; // Example API

constructor(private http: HttpClient) { }

getUsers(): Observable<any[]> {
return this.http.get<any[]>(this.apiUrl);
}
}

b) Router

The Router service is essential when navigating from one view while users perform application tasks.

We must first import the Router service as shown below.

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { AppComponent } from './app.component';
import { HomeComponent } from './home/home.component';
import { LoginComponent } from './login/login.component';

const routes: Routes = [
{ path: '', component: HomeComponent },
{ path: 'login', component: LoginComponent }
];

@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }

The next step is using the Router function in a service.

import { Injectable } from '@angular/core';
import { Router } from '@angular/router';

@Injectable({
providedIn: 'root'
})
export class AuthService {
constructor(private router: Router) {}

login(username: string, password: string): void {
// Imagine we have logic here that successfully logs in the user.
// After login, we navigate to the home page.
this.router.navigate(['/']);
}

logout(): void {
// Logic to log out the user

// After logout, redirect to login page
this.router.navigate(['/login']);
}
}

The last step is using the Router service in a component as shown below.

import { Component } from '@angular/core';
import { Router } from '@angular/router';

@Component({
selector: 'app-login',
template: `<button (click)="login()">Login</button>`
})
export class LoginComponent {
constructor(private router: Router) {}

login(): void {
// Perform login logic...
// On success, navigate to the home page
this.router.navigate(['/']);
}
}

c) ActivatedRoute

We can use the ActivatedRoute to access route parameters, query parameters, and the route's URL segments.

The first step in utilizing it is importing ActivatedRoute as shown below.

import { Injectable } from '@angular/core';
import { ActivatedRoute } from '@angular/router';

@Injectable({
providedIn: 'root'
})
export class MyService {
constructor(private route: ActivatedRoute) { }

getRouteParams(): void {

// Accessing route parameters
const id = this.route.snapshot.paramMap.get('id');
console.log('Route ID:', id);

// Accessing query parameters
const queryParam = this.route.snapshot.queryParamMap.get('paramName');
console.log('Query Parameter:', queryParam);
}
}

The second step is utilizing the AdvancedRoute in a component.

import { Component, OnInit } from '@angular/core';
import { MyService } from './my.service';

@Component({
selector: 'app-my-component',
template: `
<p>Component Content</p>

})
export class MyComponent implements OnInit {
constructor(private myService: MyService) { }

ngOnInit(): void {
this.myService.getRouteParams();
}
}

Lastly, we can set up our routing configurations.

import { NgModule } from '@angular/core';
import { Routes, RouterModule } from '@angular/router';
import { MyComponent } from './my.component';

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

@NgModule({
imports: [RouterModule.forRoot(routes)],
exports: [RouterModule]
})
export class AppRoutingModule { }

d) FormBuilder

FormBuilder is a reserved service for creating and managing forms. Below is a simple illustration of how to use the FormBuilder service.

import { Injectable } from '@angular/core';

import { FormBuilder, FormGroup, Validators } from '@angular/forms';

@Injectable({
providedIn: 'root'
})
export class FormService {
constructor(private formBuilder: FormBuilder) { }

// Method to create a form group with FormBuilder
createForm(): FormGroup {
return this.formBuilder.group({
firstName: ['', Validators.required],
lastName: ['', Validators.required],
email: ['', [Validators.required, Validators.email]],
// Add more form controls as needed
});
}

// Method to validate a form control
validateControl(controlName: string, form: FormGroup): boolean {
const control = form.get(controlName);
return control ? control.valid && control.touched : false;
}
}

Custom Angular Services

There are three custom Angular Services; business logic, data, and utility services. We will provide some Angular Service examples to illustrate how the custom services work.

a) Business Logic Services

The business logic services focus on processing and manipulating data, implementing algorithms, and performing other application-specific operations.

The illustration below shows how we can use the business logic services.

import { Injectable } from '@angular/core';

@Injectable({
providedIn: 'root'
})
export class ProductService {
private products: Product[] = [];

constructor() { }

// Method to add a product
addProduct(product: Product): void {
this.products.push(product);
}

// Method to remove a product
removeProduct(productId: number): void {
this.products = this.products.filter(p => p.id !== productId);
}
// Method to get all products
getProducts(): Product[] {
return this.products;
}

// Other business logic methods...
}

export interface Product {
id: number;
name: string;
price: number;
// Other properties...
}

The illustration below shows how we can use the service in a component.

import { Component } from '@angular/core';
import { ProductService, Product } from './product.service';

@Component({
selector: 'app-product-list',
template: `
<ul>
<li *ngFor="let product of products">
{{ product.name }} - {{ product.price | currency }}
<button (click)="removeProduct(product.id)">Remove</button>
</li>
</ul>
`
})
export class ProductListComponent {
products: Product[];

constructor(private productService: ProductService) {
this.products = this.productService.getProducts();
}

removeProduct(productId: number): void {
this.productService.removeProduct(productId);
this.products = this.productService.getProducts(); // Refresh the list
}
}

b) Data Services

The data services core function involves handling data from components, promoting reusability and maintainability.

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'; // Example API URL

constructor(private http: HttpClient) { }

// Method to fetch data from an external API
fetchData(): Observable<any> {
return this.http.get<any>(this.apiUrl);
}

// Method to post data to an external API
postData(data: any): Observable<any> {
return this.http.post<any>(this.apiUrl, data);
}

// Method to update data on an external API
updateData(id: number, data: any): Observable<any> {
const url = `${this.apiUrl}/${id}`;
return this.http.put<any>(url, data);
}

// Method to delete data from an external API
deleteData(id: number): Observable<any> {
const url = `${this.apiUrl}/${id}`;
return this.http.delete<any>(url);
}

// Other custom data handling methods...
}

Below is how we can use the custom data services in components.

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

@Component({
selector: 'app-data-list',
template: `
<ul>
<li *ngFor="let item of data">{{ item.name }}</li>
</ul>
`
})
export class DataListComponent implements OnInit {
data: any[];

constructor(private dataService: DataService) { }

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

c) Utility Services

The utility services facilitate reusable functionality such as helper functions, formatting utilities, and other shared functionalities.

import { Injectable } from '@angular/core';

@Injectable({
providedIn: 'root'
})
export class UtilityService {
constructor() { }

// Method to capitalize the first letter of a string
capitalize(value: string): string {
return value.charAt(0).toUpperCase() + value.slice(1);
}

// Method to format a date
formatDate(date: Date): string {
// Example date formatting logic
return `${date.getMonth() + 1}/${date.getDate()}/${date.getFullYear()}`;
}

// Other utility methods...
}

Below is how to use the custom utility function in a component.

import { Component } from '@angular/core';
import { UtilityService } from './utility.service';

@Component({
selector: 'app-my-component',
template: `
<p>{{ formattedDate }}</p>
<p>{{ capitalizedValue }}</p>
`
})
export class MyComponent {
formattedDate: string;
capitalizedValue: string;

constructor(private utilityService: UtilityService) {
const currentDate = new Date();
this.formattedDate = this.utilityService.formatDate(currentDate);

const stringValue = 'example';
this.capitalizedValue = this.utilityService.capitalize(stringValue);
}
}

Angular Services and Dependencies Injection

Dependency injection in Angular refers to software design patterns where classes receive their dependencies from an external source rather than creating them themselves.

Using Dependencies in Angular

The illustration below is an Angular injector handling instances of respective dependencies when creating objects.

import { Component } from '@angular/core';
import { MyService } from './my-service.service';

@Component({
selector: 'app-my-component',
templateUrl: './my-component.component.html',
styleUrls: ['./my-component.component.css']
})
export class MyComponent {
constructor(private myService: MyService) {
// 'myService' is automatically injected by Angular
}
}

Angular Service Lifecycle

Lifecycle hooks in Angular Services refer to the methods for tapping into specific points in the lifecycle of a component or directive. Lifecycle hooks are synonymous with components but we can also utilize them within a service.

Key lifecycle hooks include ngOnInit, ngOnDestroy, and DataService. Below is an example of ngOnDestroy in cleaning up dataSubscription.

import { Injectable, OnDestroy } from '@angular/core';
import { Subscription } from 'rxjs';

@Injectable({
providedIn: 'root'
})
export class DataService implements OnDestroy {
private dataSubscription: Subscription;

constructor(private apiService: ApiService) {
this.initialize();
}

initialize(): void {
// Perform initialization tasks, such as fetching initial data
this.dataSubscription = this.apiService.getData().subscribe(data => {
// Handle data
});
}

ngOnDestroy(): void {
// Clean up resources when the service is destroyed
if (this.dataSubscription) {
this.dataSubscription.unsubscribe();
}
}
}

Angular Service Worker

Service worker is a new feature in Angular that facilitates the creation of Progressive Web Apps (PWAs). It is an efficient tool because it allows Angular applications to work offline, improve load times, and offer an app-like experience to users.

The service worker is ideally a JavaScript file working in the background of browsers to intercept network requests from applications. It enables features like caching, push notifications, and background sync, thus facilitating the creation of offline-capable web applications.

We can enable the service worker using the terminal or command line below.

ng new my-app --service-worker

Enabling the service worker creates the “ngsw-config.json” file, and here is how it looks.

{
"$schema": "./node_modules/@angular/service-worker/config/schema.json",
"index": "/index.html",
"assetGroups": [{
"name": "app",
"installMode": "prefetch",
"resources": {
"files": [
"/favicon.ico",
"/index.html",
"/manifest.webmanifest"
],
"versionedFiles": [
"/*.bundle.css",
"/*.bundle.js",
"/*.chunk.js"
]
}
}, {
"name": "assets",
"installMode": "lazy",
"updateMode": "prefetch",
"resources": {
"files": [
"/assets/**"
]
}
}]
}

Angular Authentication Service

Angular authentication services are essential for managing user authentication processes, such as login, logout, registration, and managing user sessions. Below is an illustration of how to use the authentication service in Angular.

// auth.service.ts

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

@Injectable({
providedIn: 'root'
})
export class AuthService {
private loggedIn = new BehaviorSubject<boolean>(false);

constructor(private http: HttpClient) { }

login(credentials: { username: string, password: string }): Observable<any> {
// Make API call to your authentication endpoint
return this.http.post('/api/login', credentials).pipe(
tap(response => {
// Assuming the response contains a token upon successful authentication
if (response && response.token) {
localStorage.setItem('token', response.token);
this.loggedIn.next(true);
}
})
);
}

logout(): void {
localStorage.removeItem('token');
this.loggedIn.next(false);
}

isAuthenticated(): Observable<boolean> {
return this.loggedIn.asObservable();
}
}

Best Practices for Angular Services

Here is a summary of the best practices for Angular Services to ensure our code is maintainable, scalable, and performs seamlessly.

• Adhere to the Single Responsibility Principle (SRP)
• Decorate services with the “@Injectable()” decorator
• Use the “providedIn: root” in the “@Injectable()” decorator
• Use Dependency Injection to inject services into components, other services, or directives
• Keep services lean
• Avoid Stateful Services
• Use RxJS for asynchronous operations
• Always handle errors gracefully in services
• Unsubscribe from subscriptions in services to avoid memory leaks
• Write unit tests for services to ensure they behave seamlessly
• Document public APIs, methods, and essential functionalities of services using comments or dedicated documentation tools like Compodoc.
• Optimize service performance by minimizing unnecessary HTTP requests, avoiding synchronous operations, and optimizing algorithms.
  

Summary

Angular Services is the heart of Angular architecture because it provides a means for sharing data, implementing business logic, and facilitating communication between components. Learning about Angular Services is paramount to unlock the power and versatility of Angular architecture.

FAQs

1. What is the Angular service?

Angular Services is a rudimentary tool for streamlining web applications. It offers a centralized code management system for business logic by ensuring a maintainable code base.

2. What is the difference between service and component in Angular?

Components are the building blocks of Angular applications, representing the UI elements that users interact with. Services are reusable, singleton objects that encapsulate functionality and data that are not specific to any particular component.

3. When to create an Angular Service?

Create an Angular Service to encapsulate functionality or data that is reusable across components, not UI specific, share state or data, or contain cross-cutting concerns.

4. What are the benefits of Angular Services?

Angular Services provide several benefits that contribute to the overall robustness, maintainability, and scalability of Angular applications.

5. What are the types of Services in Angular?

There are three types of Angular Services; singleton, scoped, and transient services with each having a different purpose when initiating services.

6. Is Angular a web service?

No, Angular service is not a web survive because it is technically a front-end framework for building web applications.

7. What is the difference between service and provider in Angular?

In Angular, a service encapsulates a specific functionality or feature shared across components. A provider in Angular is a configuration object for defining service instantiation and provision within the application's dependency injection system.

8. How to create a service in Angular?

You can utilize the Angular CLI command “ng generate service service-name” to create a service file with your preferred name. You can then define the service's functionality within the service class by adding methods, properties, and dependencies as needed.

9. How to use services in Angular with examples?

The first step is to inject the service into the component or other service where you want to use it, typically through the constructor. You can access the service's methods and properties within the component or service. For example, if you have a UserService, you would inject it into a component like this: constructor(private userService: UserService) { }, before utilizing its methods (e.g. userService.getUser() ), within the component.

10. Is Angular a built-in service?

No, Angular itself is not a built-in service. Angular is a framework for building web applications, and it provides various built-in services such as HTTP, Router, and Forms that help developers accomplish common tasks efficiently.