let count = 0;
let prevTimestamp;

function showFPS(fps) {
  // 这里设置如何将 fps 数值输出
  // 比如你可以将其更新到某个 DOM 元素上
  console.log(fps);
}

function loop(timestamp) {
  if (prevTimestamp) {
    count++;
    // 间隔超过 1s，将之前计算的 count 输出
    if (timestamp - prevTimestamp >= 1000) {
      showFPS(Math.round((count * 1000) / (timestamp - prevTimestamp)));
      prevTimestamp = timestamp;
      count = 0;
    }
  } else {
    prevTimestamp = timestamp;
  }
  window.requestAnimationFrame(loop);
}

window.requestAnimationFrame(loop);