JSFiddle - React, Tailwind, and code Playground

HTML

<h1 id="title"> 
  START THE TIMER
</h1>

<button onclick="Decrement()">GO!</button>

<h2 id="timerText">######</h2>

<br/>
<textarea rows="15" cols="60" id="text"></textarea>

<h2 id="finish" class="finish">Copyright BibBoy &#174  2014 #ImYourMum</h2>

JavaScript

var mins = 10; //Set the number of minutes you need
   var secs = mins * 60;
   var currentSeconds = 0;
   var currentMinutes = 0;
   setTimeout(Decrement, 1000);

   // for easier testing
   secs = secs - 10 * 60 + 5;

   function Decrement() {
       currentMinutes = Math.floor(secs / 60);
       currentSeconds = secs % 60;
       if (currentSeconds <= 9) currentSeconds = "0" + currentSeconds;
       secs--;
       document.getElementById("timerText").innerHTML = currentMinutes + ":" + currentSeconds; //Set the element id you need the time put into.
       
       if (secs !== -1) {
           setTimeout(Decrement, 1000);
       } else {
           alert('you\'re done');
       }
   }