Smooth scroll page

smoothscroll.js

(function() {
  const scroller = document.scrollingElement || document.body;

  // Smooth scrolls to the bottom of the page.
  window.smoothScrollPage = (y = scroller.scrollHeight) => { 
    scroller.style.scrollBehavior = 'smooth';
    scroller.scrollTop = y;
    scroller.style.scrollBehavior = '';
  };

  // Smooth scrolls to the bottom of the page at a rate of 60fps.
  window.scrollPageSlowly = () => { 
    requestAnimationFrame(function callback(timestamp) {
      scroller.scrollBy({left: 0, top: 100, behavior: 'smooth'});
      const atBottom = scroller.getBoundingClientRect().bottom - window.innerHeight === 0;
      if (!atBottom) {
        requestAnimationFrame(callback);
      }
    });
  };
})();