infinite scroll

gistfile1.ts

Observable.fromEvent(this.scrollElement.nativeElement, 'scroll')
            .map((e: MouseEvent) => (e.target as HTMLElement).scrollTop * 100 / ((e.target as HTMLElement).scrollHeight - (e.target as HTMLElement).clientHeight))
            .pairwise()
            .filter(([h1, h2]) => h1 < h2 && h1 > 80)
            .startWith([0, 0])
            .exhaustMap((x, i) => this.notificationService.getNotifications(i).delay(1000))
            .takeWhile(notifs => notifs && notifs.list && notifs.list.length)
            .scan((acc, val) => ({ count: val.count, list: [...acc.list, ...val.list || []] }), { list: [], count: 0 });