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main.ts

index.html

import { bootstrapApplication } from '@angular/platform-browser';
import { Component, Injectable } from '@angular/core';

@Injectable({ providedIn: 'root' })
export class CounterService {
  value = 0;
  inc() { this.value++; }
  dec() { this.value--; }
}

@Component({
  selector: 'counter-a',
  standalone: true,
  template: `
    <h4>Counter A</h4>
    <p>Value: {{ counter.value }}</p>
    <button (click)="counter.inc()">+1</button>
    <button (click)="counter.dec()">-1</button>
  `
})
export class CounterA {
  constructor(public counter) {}
}

@Component({
  selector: 'counter-b',
  standalone: true,
  template: `
    <h4>Counter B</h4>
    <p>Value: {{ counter.value }}</p>
    <button (click)="counter.inc()">+1</button>
    <button (click)="counter.dec()">-1</button>
  `
})
export class CounterB {
  constructor(public counter) {}
}

@Component({
  selector: 'app-root',
  standalone: true,
  imports: [CounterA, CounterB],
  template: `
    <h3>Shared Service Across Components</h3>
    <counter-a></counter-a>
    <counter-b></counter-b>
    <p><em>Both components use the same CounterService instance.</em></p>
  `
})
export class App {}

bootstrapApplication(App);

<!doctype html>
<html lang="en">
<head>
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1">
  <title>Angular Services - Shared Service</title>
</head>
<body>
  <app-root></app-root>
</body>
</html>