JSFiddle - React, Tailwind, and code Playground

HTML

<script>
    function displayNumber()
{
    
    
  
 var card = document.getElementById('credit').value;
  
var str = "";
for(var i=1; i <= card.length-4; i++) {
   str += "*";
}
    
    ecard = str + card.substr(card.length-4);
    document.getElementById('credit').value = ecard;
    
}
</script>

  
  <form id="myform">
   <input type="text" id="credit"  onkeyup="displayNumber()">
</form>