JSFiddle - React, Tailwind, and code Playground

HTML

<!DOCTYPE html>
<!DOCTYPE html>
<html>
<head>
    <meta http-equiv="Content-Type" content="text/html; charset=utf-8" />
    <title></title>
    <meta charset="utf-8" />

</head>
<body>

    <p id="secundomer"></p>
    <input type="button" value="старт" onclick="start()" />
    <input type="button" value="стоп" onclick="stop()" />
    <input type="button" value="сброс" onclick="cancel()" />

    <script>

       var ms = 0;   //мс
       var s = 0;    //сек
       var m = 0;    //мин
       var MS = 0;   //мс
       var S = 0;    //сек
       var M = 0;    //мин
       var SM = document.getElementById("secundomer");
       var x;
           function fstart() {
                        ms++;
                   if (ms == 1000) {
                       ms = 0;
                       s += 1;
                   }
                   if (s == 60) {
                       s = 0;
                       m += 1;
                   }
                   if (m == 60) {
                       clearInterval(x);
                   }
                   MS = "00";
                   if (ms > 99)
                       MS = (ms - (ms % 10)) / 10;
                   if (ms > 9)
                       MS = "0" + (ms-(ms%10))/10;
                   if (s < 10)
                       S = "0" + s;
                   else
                       S = s;
                   if (m < 10)
                       M = "0" + m;
                   else
                       M = m;
                   SM.innerHTML = MS + ":" + S + ":" + M;
           }

          
           function start() { x = setInterval(fstart, 1)
           y=x}

        function stop()
        {
            clearInterval(y);
        }

        function cancel()
        {
           clearInterval(x);
            ms = 0;
            s = 0;
            m = 0;
            SM.innerHTML = MS + ":" + S + ":" + M;
        }


    </script>

</body>
</html>