JS Thousands Separator

HTML

<p id="output">

</p>

JavaScript

const numberWithCommas = (x) => {
  var parts = x.toString().split(".");
  parts[0] = parts[0].replace(/\B(?=(\d{3})+(?!\d))/g, ",");
  return parts.join(".");
}

let myNumber = 12401925591;

document.getElementById('output').innerHTML = numberWithCommas(myNumber);