// Spy on any element to which it is applied.
// Usage: 
...
@Directive({selector: '[mySpy]'})
export class SpyDirective implements OnInit, OnDestroy {

  constructor(private logger: LoggerService) { }

  ngOnInit()    { this.logIt(`onInit`); }

  ngOnDestroy() { this.logIt(`onDestroy`); }

  private logIt(msg: string) {
    this.logger.log(`Spy #${nextId++} ${msg}`);
  }
}