lazy-load-images#setup-p2.ts

@Directive({
  selector: 'img[appLazyLoad]'
})
export class LazyLoadDirective implements AfterViewInit {
  @HostBinding('attr.src') srcAttr = null;
  @Input() src: string;

  ngAfterViewInit() {
    this.canLazyLoad() ? this.lazyLoadImage() : this.loadImage();
  }

  private canLazyLoad() {
    return window && 'IntersectionObserver' in window;
  }

  private lazyLoadImage() { }

  private loadImage() {
    this.srcAttr = this.src;
  }
}