chronometer.js

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

  start(printTimeCallback) {
    this.intervalId = setInterval(() => {
      this.currentTime += 1;
      if (printTimeCallback) {
        printTimeCallback();
      }
    }, 1000);
  }

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

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

  computeTwoDigitNumber(value) {
    //oneliner version of solution
    return ("0" + value).slice(-2);
    //convert to string and then check the .length of the string
    // const str = value.toString();
    // if (str.length === 1) {
    //   return "0" + str;
    // } else {
    //   return str;
    // }

    // //check the value is less than ten, then it needs a 0 in front. Else no
    // if (value < 10) {
    //   return "0" + value.toString();
    // } else {
    //   return value.toString();
    // }
  }

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

  reset() {
    this.currentTime = 0;
  }

  split() {
    let currentMinutes = this.getMinutes();
    let currentSeconds = this.getSeconds();
    let minsString = this.computeTwoDigitNumber(currentMinutes);
    let secsString = this.computeTwoDigitNumber(currentSeconds);
    const timeString = `${minsString}:${secsString}`;
    return timeString;
  }
}