Number With Comma

function numberWithComma(number) {
  // convert number to string
  let str = String(number)

  let s = ''
  let count = 0
  for (let i = str.length - 1; i >= 0; i--) {
    s = str[i] + s
    count++
    // add a comma to every three numbers
    if (count % 3 == 0 && i != 0) {
      s = ',' + s
    }
  }
  return s
}

// numberWithComma(111111)
// 111,111

// numberWithComma(123456789)
// 123,456,789