JSFiddle - React, Tailwind, and code Playground

HTML

<input type="text"  onblur="numberWithCommas()" name="abc" id="abc" placeholder="abc" />

JavaScript

function numberWithCommas() {
  var x = document.getElementById('abc').value;
  var y = x.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");
  document.getElementById('abc').value = y;
}