const speed = document.querySelector('.speed');
const speedBar = document.querySelector('.speed-bar');
const video = document.querySelector('.flex');

const handleMove = (e) => (target) => (bar) => (video) => {
  const y = e.pageY - target.offsetTop;
  const percent = y / target.offsetHeight;
  const min = 0.4;
  const max = 4;
  const height = Math.round(percent * 100) + '%';
  const playbackRate = percent * (max - min) + min;
  bar.style.height = height;
  bar.textContent = playbackRate.toFixed(2) + '×';
  video.playbackRate = playbackRate;
};

speed.addEventListener('mousemove', (e) =>
  handleMove(e)(speed)(speedBar)(video)
);