lazyload2.service.ts

export class LazyLoadService {
  // ...

  private _loadAheadCount = 2; // default 2
  get loadAheadCount() { return this._loadAheadCount; }
  set loadAheadCount(value: number) {
    this._loadAheadCount = value;
  }

  // announce intersecting index to [lazyLoad] directives
  private intersection$ = new Subject<any>();
  announcedIntersection = this.intersection$.asObservable();
  announceIntersection(params: object) { // { index: number, state: IntersectionState }
    this.intersection$.next(params);
  }