JSFiddle - React, Tailwind, and code Playground

HTML

<div id="txtMilli"> </div>
<div id="txtSeconds"> </div>
<div id="txtMinutes"> </div>

<button id="myButton">
   Toggle Stopwatch!
</button>

JavaScript

var milli = 0;
    var seconds = 0;
    var minutes = 0;
    var onOff = 0;

    var txtMilli = document.getElementById("txtMilli");
    var txtSeconds = document.getElementById("txtSeconds");
    var txtMinutes = document.getElementById("txtMinutes");

    function startCounting(){        
        if (milli >999) { milli = 0; if (seconds <60) {seconds +=1} }
        else {milli +=1;}
        if (seconds >59) {seconds = 0; minutes += 1;}

        if (milli > 10) {txtMilli.innerHTML = "0" + milli;}
        if (milli < 10) {txtMilli.innerHTML = "" + milli;}
    }

    function theTimer(){
        if (onOff == 0) {
            onOff = 1;
            timer = setInterval(startCounting, 1);
        } else if (onOff == 1) {
            onOff = 0;
            clearInterval(timer);
        }
    }
    
    myButton.onclick = theTimer;