JSFiddle - React, Tailwind, and code Playground

HTML

<button id="timer1">Try it</button>
<button id="timer2">Try it</button>
<button id="timer3">Try it</button>

JavaScript

var timerObject = function(){
	this.startTime = 60; //in Minutes
	this.doneClass = "done"; //optional styling applied to text when timer is done
	this.space = '       ';

 	return this;
};

timerObject.prototype.startTimer = function(duration, display) {
  var me = this, 
  	  timer = duration,
      minutes, seconds;
  var intervalLoop = setInterval(function() {
    minutes = parseInt(timer / 60, 10)
    seconds = parseInt(timer % 60, 10);
    minutes = minutes < 10 ? "0" + minutes : minutes;
    seconds = seconds < 10 ? "0" + seconds : seconds;
    display.textContent = "00" + me.space + minutes + me.space + seconds;
    if (--timer < 0) {
      // not sure about this part, because of selectors
      //document.querySelector("#timer").classList.add(me.doneClass);
      clearInterval(intervalLoop);
    }
  }, 1000);
};

var timer1 =  document.getElementById("timer1");
var timer2 =  document.getElementById("timer2");
var timer3 =  document.getElementById("timer3");

var t1 = new timerObject();
var t2 = new timerObject();
t1.startTimer(10,timer1);
t2.startTimer(20,timer2);