class Clock { constructor({ template }) { this.template = template; } render() { let date = new Date(); let hours = date.getHours(); if (hours < 10) hours = '0' + hours; let mins = date.getMinutes(); if (mins < 10) mins = '0' + mins; let secs = date.getSeconds(); if (secs < 10) secs = '0' + secs; let output = this.template .replace('h', hours) .replace('m', mins) .replace('s', secs); console.log(output); } stop() { clearInterval(this.timer); } start() { this.render(); this.timer = setInterval(() => this.render(), 1000); } } let clock = new Clock({template: 'h:m:s'}); clock.start();