Lifecycle of an Angular service

Understanding the lifecycle of an Angular service is crucial for effectively managing dependencies and ensuring optimal performance in your application. Here’s a breakdown of the lifecycle of an Angular service:

1. Creation

When a service is first requested by a component, directive, or another service, Angular’s dependency injection system creates an instance of the service. This happens only once if the service is provided at the root level or a module level, ensuring a singleton instance.

@Injectable({
  providedIn: 'root',
})
export class MyService {
  constructor() {
    console.log('MyService instance created');
  }
}

2. Injection

The created instance is then injected into the requesting component, directive, or service. This is done through the constructor of the class where the service is needed.

@Component({
  selector: 'app-my-component',
  template: `
{{ message }}
`,
})
export class MyComponent {
  message: string;

  constructor(private myService: MyService) {
    this.message = this.myService.getMessage();
  }
}

3. Usage

The methods and properties of the service are used by the component, directive, or another service. This is where the main functionality of the service is utilized.

@Injectable({
  providedIn: 'root',
})
export class MyService {
  getMessage() {
    return 'Hello from MyService!';
  }
}

4. Destruction

Angular does not explicitly destroy services. Instead, services are subject to JavaScript’s garbage collection. When there are no more references to the service instance, it becomes eligible for garbage collection. This typically happens when the component or module that requested the service is destroyed.

Key Points to Remember

• Singleton Services: When a service is provided at the root level (providedIn: 'root'), it is a singleton, meaning only one instance of the service exists throughout the application.
• Scoped Services: When a service is provided at a module or component level, it can have multiple instances, each scoped to the module or component where it is provided.
• Lazy Loading: Services provided in lazy-loaded modules are created only when the module is loaded, which can help optimize performance by loading services only when needed.

Example Scenario

• App Initialization: The application starts, and no services are instantiated yet.
• Component Request: A component requests a service.
• Service Creation: Angular’s DI system creates an instance of the service.
• Service Injection: The service instance is injected into the component.
• Service Usage: The component uses the service’s methods and properties.
• Component Destruction: When the component is destroyed, the service instance remains if it is a singleton. If the service is scoped to the component, it becomes eligible for garbage collection.

Understanding this lifecycle helps in designing services that are efficient, reusable, and maintainable.

Happy coding!! 😊