Angular Dependency Injection

Dependency Injection (DI) is a design pattern used in Angular to make your application more maintainable and testable. It allows you to manage dependencies between classes and provides a way to create instances of classes without explicitly instantiating them.

Why Use Dependency Injection?

• Improved Testability: By using DI, you can easily mock dependencies in your tests, which makes unit testing easier.
• Loose Coupling: DI helps in reducing the coupling between classes, making your code more modular and easier to maintain.
• Scalability: It provides a way to manage dependencies at runtime, which is helpful in large applications.

How Dependency Injection Works

Angular uses the Angular DI container to manage dependencies. When you create a component or a service, Angular automatically injects the required dependencies into the constructor of the component or service.

Types of Dependencies

• Services: These are singletons that are shared across the application.
• Components: These are reusable UI elements.
• Directives: These are used to transform HTML elements.
• Pipes: These are used to transform data into a different format.

Dependency Injection in Components

Here's an example of how to use DI in a component:

import { Component } from '@angular/core';
import { LoggerService } from './logger.service';

@Component({
  selector: 'app-root',
  template: `<h1>{{ message }}</h1>`
})
export class AppComponent {
  message: string;

  constructor(private logger: LoggerService) {
    this.message = 'Hello, Angular!';
    this.logger.log('Component initialized');
  }
}

In this example, the LoggerService is injected into the AppComponent constructor.

Dependency Injection in Services

Services are often used to handle business logic. Here's an example of a service that uses DI:

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

@Injectable({
  providedIn: 'root'
})
export class LoggerService {
  log(message: string) {
    console.log(message);
  }
}

In this example, the LoggerService is marked as @Injectable, which makes it available for DI.

Conclusion

Dependency Injection is a powerful tool in Angular that helps you create maintainable and testable applications. By understanding how DI works, you can make your Angular applications more robust and scalable.

For more information on Angular Dependency Injection, you can read Angular Dependency Injection Guide.

Angular Dependency Injection