Timo's timer class

timer.js

class Timer {
  constructor(startTime = 0, onUpdate = () => {}) {
    this.startTime = startTime;
    this.onUpdate = onUpdate;
  }

  offset = null;
  interval = null;
  recording = false;

  start = () => {
    this.recording = true;
    this.offset = Date.now();
    this.interval = setInterval(this.update, 1000);
  };

  update = () => {
    const newTime = this.startTime + this.calculateTimeOffset();
    this.startTime = newTime;
    this.onUpdate(newTime);
  };

  stop = () => {
    clearInterval(this.interval);
    this.interval = null;
    this.recording = false;
  };

  calculateTimeOffset = () => {
    const now = Date.now();
    const newOffset = now - this.offset;
    this.offset = now;
    return newOffset;
  };
}

export default Timer;