JSFiddle - React, Tailwind, and code Playground

HTML

<th>Test Time</th>
  <td><input name="timer" id="timer"/></td>

JavaScript

var myVar=setInterval(function(){myTimer()},1000);

function myTimer()
{
var d=new Date();
var t=d.toLocaleTimeString();
document.getElementById("timer").value=t;
}