dependency-inversion-1.ts

class EmailBroadcaster {
  send(event: Event, user: User) {
    const description = `New event ${event.name} occured at ${event.getTimestamp()}`
    emailService.send({ to: user.email, subject: event.name, body: description })
  }
}

class NotificationHandler {
  private mailer: EmailBroadcaster

  constructor() {
    this.mailer = new EmailBroadcaster()
  }

  public broadcast(event: Event, user: User) {
    this.mailer.send(event, user)
  }
}

function onAccountCreated(event: Event, user: User) {
  const notifications = new NotificationHandler()
  notifications.broadcast(event, user)
}