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if (window.localStorage.getItem("fpson") == undefined || window.localStorage.getItem("fpson") == "1") {
  var rAF = function () {
      return (
          window.requestAnimationFrame ||
          window.webkitRequestAnimationFrame ||
          function (callback) {
              window.setTimeout(callback, 1000 / 60);
          }
      );
  }();
  var frame = 0;
  var allFrameCount = 0;
  var lastTime = Date.now();
  var lastFameTime = Date.now();
  var loop = function () {
      var now = Date.now();
      var fs = (now - lastFameTime);
      var fps = Math.round(1000 / fs);

      lastFameTime = now;
      // 不置 0，在动画的开头及结尾记录此值的差值算出 FPS
      allFrameCount++;
      frame++;

      if (now > 1000 + lastTime) {
          var fps = Math.round((frame * 1000) / (now - lastTime));
          if (fps <= 5) {
              var kd = `一秒一帧😣`
          } else if (fps <= 15) {
              var kd = `非常难受🥴`
          } else if (fps <= 25) {
              var kd = `较低帧率🥲`
          } else if (fps < 35) {
              var kd = `不太流畅😑`
          } else if (fps <= 45) {
              var kd = `还不错哦😊`
          } else {
              var kd = `十分流畅🌹`
          }
          document.getElementById("fps").innerHTML = `FPS:${fps} ${kd}`;
          frame = 0;
          lastTime = now;
      };

      rAF(loop);
  }

  loop();
} else {
  document.getElementById("fps").style = "display:none!important"
}

代码来源：
这个网站的站长：https://ezgx.site/