JSFiddle - React, Tailwind, and code Playground

HTML

Remaining <span id="placetoshowtime"></span>
<script>
function timer()
    {
      count=count-1;
      if (count <= 0)
      {
         alert('he download has starte');
         clearInterval(counter);
         return;
      }
    
      document.getElementById("placetoshowtime").innerHTML = count; //display the time to user
    }

    var count=30; //30 seconds
    var counter = setInterval('timer()',1000); //1000 will  run it every 1 second
</script>