JSFiddle - React, Tailwind, and code Playground

HTML

<div id="timer"></div>
<a id="start" >start<a>
<a id="stop">stop<a>

JavaScript

$(document).ready(function(){
var handler = null;
var startTime = 0;
function startTimer(){     
    startTime = (new Date()).getTime();
    handler = setInterval(function(){showTime()},1000);
}
function showTime(){   
    var senconds = ((new Date()).getTime() - startTime)/1000 + 's';
    $('#timer').text(senconds);
}
function stopTimer(){
    clearInterval(handler);
}
$('#start').click(startTimer);
$('#stop').click(stopTimer);

});