JSFiddle - React, Tailwind, and code Playground

HTML

<body onload="init()">
<label id=count_label_ms></label>
<br>
<p>
    <input type=button value="Start" onclick="start()" />
    <input type=button value="Pause" onclick="pause()" />
    <input type=button value="Reset" onclick="reset()" />
    <input type=button value="Stop" onclick="stop()" />
</p>
</body>

JavaScript

var params = {
               countms:0,
               intervalTxt:null,
               id: "count_label_ms",
               startInit: 1,
               char: "segundos",
               isDate: false, //true or false
               speed: 10000 //somente para tipo Date
             };

function init(){
     document.getElementById(params.id).innerHTML = 0 + " "+params.char; 
    if (params.isDate) {
                    var dateObj = new Date(0);
                    dateObj.setHours(0);
        document.getElementById(params.id).innerHTML = dateFormat(dateObj) + " "+params.char;
    }
}

function start()
{
    if (params.intervalTxt == null) {
        params.intervalTxt = setInterval(function() {
            var content = (parseFloat(params.countms) / 100) + " "+params.char; 
            if (params.isDate) {
                params.countms = params.countms + params.speed;
                var dateObj = new Date(0);
                    dateObj.setHours(0);
                    dateObj.setMilliseconds(parseFloat(params.countms) / 100);
                    content = dateFormat(dateObj) + " "+params.char;
            } else {
                params.countms++;
            }
            document.getElementById(params.id).innerHTML = content;
        }, params.startInit);
    }
}

function pause()
{
    if (params.intervalTxt != null) {
        clearInterval(params.intervalTxt);
        params.intervalTxt = null;
    }
}

function reset()
{
    clearInterval(params.intervalTxt);
    params.intervalTxt = null;
    params.countms = 0;
    var content = 0 + " "+params.char;  
    if (params.isDate) {
        params.countms = params.countms + params.startInit + params.speed;
        var dateObj = new Date(0);
            dateObj.setHours(0);
            dateObj.setMilliseconds(0);
            content = dateFormat(dateObj) + " "+params.char;
    } else {
      params.countms++;
    }
    document.getElementById(params.id).innerHTML = content;
    start();
}

function stop()
{
...