http://www.codewars.com/kata/ninety-nine-thousand-nine-hundred-ninety-nine/train/javascript

99999.js

const numberToEnglish = n => {
  //handle exceptions; zero, >/< prescribed range, non-integers
  if (n === 0)
    return 'zero';
  if (n < 0 || n > 99999)
    return '';
  let strn = String(n).padStart(5,'0');  //convert to uniform, five digit string
  if (strn.includes('.'))
    return '';
  //get strings for thousands, hundreds, and tens
  let thousands = strn.substring(0,2);
  if (thousands !== '00')
    var tString = twoDigit(thousands)+ ' thousand ';
  else
    var tString = '';
  let hundreds = strn.substring(2,3);
  if (hundreds !== '0')
    var hString  = oneDigit(hundreds) + ' hundred ';
  else
    var hString = '';
  let tens = strn.substring(3);
  if (tens !== '00')
    var teString = twoDigit(tens);
  else
    var teString = '';
  //join strings together and trim excess whitespace  
  return (tString+hString+teString).trim();
}


let singleDigits = ['', 'one', 'two', 'three', 'four', 'five', 'six', 'seven', 'eight', 'nine'];
const oneDigit = a => {  //a is a one char string
  return singleDigits[parseInt(a)];
}

let doubleDigits = ['', '', 'twenty', 'thirty', 'forty', 'fifty', 'sixty', 'seventy', 'eighty', 'ninety'];
const twoDigit = b => { //b is a 2 char string
  if (b[0] === '0')
    return oneDigit(b[1]);
  //handle special cases 10-19
  else if (b[0] === '1') {
    if (b[1] === '0')
      return 'ten';
    else if (b[1] === '1')
      return 'eleven';
    else if (b[1] === '2')
      return 'twelve';
    else if (b[1] === '3')
      return 'thirteen';
    else if (b[1] === '5')
      return 'fifteen';
    else if (b[1] === '8')
      return 'eighteen';
    else
      return oneDigit(b[1])+'teen';
  }
  else{
    if (b[1] === '0')
      return doubleDigits[parseInt(b[0])];
    else
      return doubleDigits[parseInt(b[0])] + ' ' + oneDigit(b[1]);
  }      
}