Convert a number to a string of its equivalent in rupiah (TypeScript)

rupiah.ts

// JavaScript Code Snippet
// Convert integer to Rupiah & vice versa
// https://gist.github.com/845309
//
// Copyright 2011-2012, Faisalman
// Licensed under The MIT License
// http://www.opensource.org/licenses/mit-license

/**
 * Convert a number to a string of its equivalent in rupiah
 * @param {number} nominal - The number to be converted to rupiah.
 */
export function convertToRupiah(nominal: number) {
  if (nominal === 0) return "Rp. 0";

  if (!nominal.toString().match(/^\d+$/)) {
    throw new Error("Nominal must be an integer");
  }

  let rupiah = "";
  const reversedNominal = nominal.toString().split("").reverse().join("");
  for (let i = 0; i < reversedNominal.length; i++) {
    if (i % 3 === 0) {
      rupiah += reversedNominal.substr(i, 3) + ".";
    }
  }
  return (
    "Rp. " +
    rupiah
      .split("", rupiah.length - 1)
      .reverse()
      .join("")
  );
}

/**
 * Convert a string of rupiah to a number
 * @param {string} rupiah - the string that contains the rupiah amount
 * @returns a number.
 */
export function convertRupiahToNumber(rupiah: string) {
  return parseInt(rupiah.replace(/,.*|[^0-9]/g, ""), 10);
}