Setting up the Animation Timer

The render and onFrame functions look exactly the same as in the previous examples:

function onFrame() {
  elapsedTime = (new Date).getTime() - initialTime;
  if (elapsedTime < animationRate) return;

  let steps = Math.floor(elapsedTime / animationRate);
  while (steps > 0) {
    animate();
    steps -= 1;
  }

  initialTime = (new Date).getTime();
}

function render() {
  initialTime = (new Date).getTime();
  setInterval(onFrame, animationRate / 1000);
}