JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text" id="num">

<button onclick="myFunction()">submit</button>

<p id="output"></p>

JavaScript

function myFunction() {
	num = document.getElementById('num').value;
  var $output = document.getElementById("output");

  if (num.length < 4) {
     $output.innerHTML = '';
     return false;
  }
  
  var one = num.substring(2, 4); //getting letter at 3rd and 4th position
  $output.innerHTML = one;
}

window.onkeypress = function(evt)
{
   evt = (evt) ? evt : window.event;
   var charCode = (evt.which) ? evt.which : evt.keyCode;

   if (charCode >= 32 && (charCode < 48 || charCode > 57)) {
      return false;
    }
    
    return true;
}