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main.ts

index.html

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

@Injectable({ providedIn: 'root' })
class MessageService {
  getMessage() { return 'Hello from a service!'; }
}

@Component({
  selector: 'app-root',
  standalone: true,
  template: `<h1>{{ msg.getMessage() }}</h1>`
})
class App {
  msg = inject(MessageService);
}

bootstrapApplication(App);

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