chronometer.js

class Chronometer {
  constructor() {
    this.currentTime = 0;
    this.intervalId = null;
  }

  start(callback) {
    this.intervalId = setInterval(() => { 
      this.currentTime++;
      if (typeof callback === 'function') {
        callback();
      }
    }, 1000);
  }

  getMinutes() {
    return Math.floor(this.currentTime / 60);
  }

  getSeconds() {
    return this.currentTime % 60;
  }

  computeTwoDigitNumber(value) {
    let stringValue = String(value);
    let paddedString = '00' + stringValue;
    return paddedString.slice(-2);
  }

  stop() {
    clearInterval(this.intervalId);
  }

  reset() {
    this.currentTime = 0;
  }

  split() {
    const minutes = this.getMinutes();
    const seconds = this.getSeconds();

    const formattedMinutes = this.computeTwoDigitNumber(minutes);
    const formattedSeconds = this.computeTwoDigitNumber(seconds);

    return `${formattedMinutes}:${formattedSeconds}`;
  }
}

// The following is required to make unit tests work.
/* Environment setup. Do not modify the below code. */
if (typeof module !== 'undefined') {
  module.exports = Chronometer;
}