FrameCounter.js

(function () {
  var d = time(), frames = 0;

  function time() {
    return parseInt(new Date() / 1000);
  }

  function fpsCounter() {
    if (d != time()) {
      console.log(frames + ' fps');
      frames = 0;
      d = time();
    }
    frames++;
    window.requestAnimationFrame(fpsCounter)
  }

  fpsCounter();
})()