Class Watch in JS

'use strict';

class Clock {
  constructor(options) {
    this._template = options.template;
  }

  start() {
    this._render();

    this._timer = setInterval(() => {
      this._render();
    }, 1000)

  }

  stop(){
    clearInterval(this._timer)
  }

  _render(){

    let currentDate = new Date();

    let hours = ('0' + currentDate.getHours()).slice(-2);
    let minutes = ('0' + currentDate.getMinutes()).slice(-2);
    let seconds = ('0' + currentDate.getSeconds()).slice(-2);

    let timeString = this._template
      .replace('h', hours)
      .replace('m', minutes)
      .replace('s', seconds);

    console.log(timeString);

  }

}

class ExtendedClock extends Clock {
  constructor(options) {
    super(options);
    this._precision = options.precision;
  }

  start() {
    this._render();

    this._timer = setInterval(() => {
      this._render();
    }, this._precision)

  }

}

let clock = new ExtendedClock({
  template: 'h:m:s',
  precision: 2000,
});

clock.start();

setTimeout(() => {
  clock.stop()
}, 6500);