4: Add Services

[examples/angular-tour-of-heroes] / src / app / messages / messages.component.html

<div *ngIf="messageService.messages.length">
  <h2>Messages</h2>
  <button class="clear" (click)="messageService.clear()">clear</button>
  <div *ngFor="let message of messageService.messages">{{message}}</div>
</div>