Simple example of smooth scrolling using vanilla JS

smoothScroll.js

const duration = 0.06 * 800; // 800ms (60fps)
const from = scrollY;
const to = document.documentElement.scrollHeight;
const change = to - from;
let time = 0;

function ease(change, duration, from, time) {
  time /= duration / 2;
  
  if (time < 1) {
    return change / 2 * time * time + from;
  }
  
  time--;
  return -change / 2 * (time * (time - 2) - 1) + from;
}

function smoothScroll() {
  if (time >= duration) {
    return;
  }
  
  requestAnimationFrame(smoothScroll);
  
  const y = ease(change, duration, from, ++time);
  scrollTo(0, y);
}

smoothScroll();