Override Number.toLocaleString("fa-IR") and change its thousands separator character for Persian numbers

Question

I need to reformat numeric values based on the locale format, and to do this I use Number.toLocaleString("LOCAL") function. In Iran, the majority of people prefer to use , as a thousands separator character, but Number.toLocaleString("fa-IR") uses ٬ (Technically٬ it is correct).

Although you can replace the character by using the following code, is there any way to override the Number.toLocaleString("fa-IR")'s functionality?

function formatNumber(number) {
  let string = number.toLocaleString('fa-IR'); // ۱۲٬۳۴۵٫۶۷۹
  number = number.replace(/\٬/g, ",‬");
  return string;
}
    
formatNumber(12345.6789); // the result: ۱۲,۳۴۵٫۶۷۹

PS: I know there are plenty of similar code-snippets out there, but I would like to override the built-in function (if possible).

Answer 1

If you're happy to change the prototype of Number, then yes. It is often warned against changing the prototype of a built in class, as that could mess with other libraries and such.

Forging ahead regardless:

const old = Number.prototype.toLocaleString;
Number.prototype.toLocaleString = function(locale)
{
  let result = old.call(this, locale);
  if(locale === 'fa-IR')
  {
    result = result.replace(/\٬/g, ",‬");
  }
  return result;
}