sliding a browser window

gistfile1.txt

let slideWindow = (destX, time) => new Promise(resolve => {
  let startTime = Date.now();
  let stopTime = startTime + time;
  let startX = screenX;
  let distance = destX - startX;
  let speed = distance / time;
  let animationFrame = () => {
    if (Date.now() < stopTime) {
      let timeElapsed = Date.now() - startTime;
      screenX = startX + speed * timeElapsed;
      window.requestAnimationFrame(animationFrame);
    } else {
      screenX = destX;
      resolve();
    }
  }
  window.requestAnimationFrame(animationFrame);
});