ghostfolio/.agents/skills/angular-developer/references/creating-services.md

Creating and Using Services

Services in Angular are reusable pieces of code that handle data fetching, business logic, or state management that multiple components or other services need to access.

Creating a Service

You can generate a service using the Angular CLI:

ng generate service my-data

Or you can manually create a TypeScript class and decorate it with @Injectable().

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

@Injectable({
  providedIn: 'root',
})
export class BasicDataStore {
  private data: string[] = [];

  addData(item: string): void {
    this.data.push(item);
  }

  getData(): string[] {
    return [...this.data];
  }
}

The providedIn: 'root' Option

Using providedIn: 'root' is the recommended approach for most services. It tells Angular to:

• Create a single instance (singleton) for the entire application.
• Make it available everywhere automatically, without needing to list it in any providers array.
• Enable tree-shaking, meaning the service is only included in the final JavaScript bundle if it is actually injected somewhere.

Injecting a Service

Once a service is created, you can inject it into components, directives, or other services using the inject() function.

Injecting into a Component

import {Component, inject} from '@angular/core';
import {BasicDataStore} from './basic-data-store.service';

@Component({
  selector: 'app-example',
  template: `
    <div>
      <p>Data items: {{ dataStore.getData().length }}</p>
      <button (click)="dataStore.addData('New Item')">Add Item</button>
    </div>
  `,
})
export class Example {
  // Inject the service as a class field
  dataStore = inject(BasicDataStore);
}

Injecting into Another Service

Services can inject other services in the exact same way.

import {Injectable, inject} from '@angular/core';
import {AdvancedDataStore} from './advanced-data-store.service';

@Injectable({
  providedIn: 'root',
})
export class BasicDataStore {
  // Injecting another service
  private advancedDataStore = inject(AdvancedDataStore);

  private data: string[] = [];

  getData(): string[] {
    // Combine data from this service and the injected service
    return [...this.data, ...this.advancedDataStore.getData()];
  }
}

Advanced Service Patterns

While providedIn: 'root' covers most scenarios, you may sometimes need:

• Component-specific instances: If a component needs its own isolated instance of a service, provide it directly in the component's @Component({ providers: [MyService] }) array.
• Factory providers: For dynamic creation.
• Value providers: For injecting configuration objects.