smoothScrollTop.ts

export default function smoothScrollTop(): Promise<null> {
  let lastScrollTop = Infinity;
  return new Promise((resolve) => {
    const smoothScrollTopImpl = () => {
      const top = document.documentElement.scrollTop || document.body.scrollTop;
      if (top > 0 && lastScrollTop > top) {
        lastScrollTop = top;
        window.requestAnimationFrame(smoothScrollTopImpl);
        window.scrollTo(0, top - (top / 8));
      } else {
        lastScrollTop = Infinity;
        resolve(null);
      }
    };
    setTimeout(() =>  smoothScrollTopImpl(), 10);
  });
}