A simple fps counter

FPSCounter.js

import getTimeMethod from './getTimeMethod';

class FPSCounter {  
  constructor() {
    this._getTime = getTimeMethod();
    this._fps = 0;
    this._prevTime = 0;
    this._frames = 0;
    
    this.startTick();
  }

  startTick() {
    this._prevTime = this._getTime();
  }

  tick() {
    const currentTime = this._getTime();

    this._frames++;

    if (currentTime - this._prevTime > 1000) {
      this._fps = Math.round(this._frames * 1000 / (currentTime - this._prevTime));
      this._prevTime = currentTime;
      this._frames = 0;
    }
  }
  
  getFPS() {
    return this._fps;
  }
}

export {
  FPSCounter as default,
};

getTimeMethod.js

function getTimeMethod() {
  return window.performance && window.performance.now
    ? () => window.performance.now()
    : () => Date.now();
}

export {
  getTimeMethod as default,
};

const counter = new FPSCounter();

function update() {
  requestAnimationFrame(b);
  counter.tick();
  console.log(counter.getFPS());
}

update();