// A költséget srtingként, nem számként kaptuk
koltseg ='4324';
Number(koltseg).toLocaleString('fr-FR')
// 4 324

const n = 716298462;
const formatted = n.toLocaleString('en-US');
console.log(formatted)
//716,298,462

How to Use Comma as Thousand Separator in JavaScript
https://www.codingem.com/comma-thousand-separator-in-javascript/

Stop Writing JavaScript Like This:
https://javascript.plainenglish.io/stop-writing-javascript-like-this-a7fafbe451a5

https://babeljs.io/repl