new Intl.NumberFormat('ja-JP', { style: 'currency', currency: 'JPY' }).format(number);

let digits = number.toFixed(2).toString()
digits.replace(/(\d)(?=(\d{3})+\b)/g, "$1,");

let digits = number.toFixed(2).toString()
digits.replace(/\B(?=(\d{3})+\b)/g, ",");

let digits = number.toFixed(2).toString()
let matcher = /(\d)(?=(?:\d{3})+\b)/g

while (matcher.test(digits)) {
  let first = digits.slice(0, matcher.lastIndex);
  let second = digits.slice(matcher.lastIndex);
  digits = first + "," + second
}

let digits = number.toFixed(2).toString()
let matcher = /(\d+)(\d{3})/

while (matcher.test(digits)) {
  digits = digits.replace(matcher, "$1,$2");
}