@Directive({
  selector: '[carousel]'
})
export class CarouselDirective implements OnInit, OnDestroy {
  // ...
  private _autoplayDelay: number;

  @Input('carouselWithDelay')
  set autoplayDelay(autoplayDelay: number) {
    this._autoplayDelay = autoplayDelay;
  }

  get autoplayDelay() {
    return this._autoplayDelay || 1000;
  }
}