I'm trying to make a thousand comma separator for JavaScript calculator.

But something works weird for me.

Here is the code that should work:

var commas = result.textContent.toLocaleString("en-US");

var commas = result.textContent.toString().replace(/\B(?=(\d{3})+(?!\d))/g, ",");

result.innerHTML=commas;

It works only for 1st separator, but when it goes further it looks weird. What am I doing wrong?

Here are the screenshots: image1 image2

Here is the link to calculator:

https://codesandbox.io/s/thirsty-rgb-2rp6dv?file=/js/script.js

UPD: If there's more than 4 numbers it shows NaN: NaN error

Thank you in advance!