JSFiddle - React, Tailwind, and code Playground

HTML

<span id="timer"></span>

JavaScript

var count= 2700; // will count down from 45 mins
var counter=setInterval(timer, 1000);
function timer()
{
  count=count-1;
  if (count <= 0)
  {
     clearInterval(counter);
     return;
  }
 document.getElementById("timer").innerHTML=count + " secs";
}