Vertical scroll on page

gistfile1.txt

window.requestAnimationFrame(function step(timestamp) {
  if (!start) start = timestamp;
  // Elapsed milliseconds since start of scrolling.
  let time = timestamp - start;
  // Get percent of completion in range [0, 1].
  let percent = Math.min(time / duration, 1);

  window.scrollTo(0, startingY + diff * percent);

  // Proceed with animation as long as we wanted it to.
  if (time < duration) {
    window.requestAnimationFrame(step);
  }
});