JSFiddle - React, Tailwind, and code Playground

JavaScript

var x=12345652457.557;
x=x.toString();
var afterPoint = '';
if(x.indexOf('.') > 0)
   afterPoint = x.substring(x.indexOf('.'),x.length);
x = Math.floor(x);
x=x.toString();
var lastThree = x.substring(x.length-3);
var otherNumbers = x.substring(0,x.length-3);
if(otherNumbers != '')
    lastThree = ',' + lastThree;
var res = otherNumbers.replace(/\B(?=(\d{2})+(?!\d))/g, ",") + lastThree + afterPoint;

alert(res);