fps.js

(function () {
  var start;
  var isRunning = false;
  var frames = 0;
  var intervalId;
  var entries = [];
  
  function onFrame () {
    if (isRunning) {
      window.requestAnimationFrame(onFrame);
      frames = frames + 1;    
    }
  }

  window.FPS = {
    getFPS: function () {
      var totalTime = (Date.now() - start) / 1000;
      return frames / totalTime;
    },
    
    printResults: function () {
      entries.forEach(function (entry) {
        if (entry < 59) {
          console.warn(entry);
        } else {
          console.info(entry);
        }
      });  
    },

    reset: function () {
      start = Date.now(); 
      frames = 0;
    },

    start: function () {
      start = Date.now();
      isRunning = true;
      window.requestAnimationFrame(onFrame);
    },

    stop: function () {
      start = null;
      isRunning = false;
    },

    startTrack: function () {
      this.reset();
      this.start();

      intervalId = setInterval(function () {
        entries.push(this.getFPS());
        this.reset();
      }.bind(this), 1000);
    },
    
    stopTrack: function () {
      this.stop();
      clearInterval(intervalId);
    }
  }
}());