Auto-scroller with ease and duration for screen recording and demo

auto-scroll.js

function scrollToBottom(duration) {
  const currentPosition = window.pageYOffset;
  const targetPosition = document.documentElement.scrollHeight - window.innerHeight;
  const distance = targetPosition - currentPosition;
  const startTime = performance.now();

  function scrollStep(timestamp) {
    const elapsed = timestamp - startTime;
    const progress = Math.min(elapsed / duration, 1);
    const easing = quadraticEaseInOut(progress);
    const newPosition = currentPosition + distance * easing;
    window.scrollTo(0, newPosition);

    if (elapsed < duration) {
      window.requestAnimationFrame(scrollStep);
    }
  }

  function quadraticEaseInOut(t) {
    if (t < 0.5) {
      return 2 * t * t;
    } else {
      return (-2 * t * t) + (4 * t) - 1;
    }
  }

  window.requestAnimationFrame(scrollStep);
}

scrollToBottom(10000);