convert numbers to words up to 1e6 - 1

numbers_two_words.js

// convert numbers to words up to 1e6 - 1

function number2words(n) {
  let ones = 'zero one two three four five six seven eight nine'.split(' ');
  let tens = 'zero ten twenty thirty forty fifty sixty seventy eighty ninety'.split(' ');
  let teens = 'thir four fif six seven eigh nine'.split(' ');
  
  let w = (n) => {
    if (n <   10) return ones[n];
    if (n <   13) return 'ten eleven twelve'.split(' ')[n - 10];
    if (n <   20) return teens[n - 13] + 'teen';
    if (n <  100) return tens[n/10|0] + (n%10 === 0 ? '' : '-' + ones[n%10]);
    if (n < 1000) return ones[n/100|0] + ' hundred' + (n%100 === 0 ? '' : ' ' + w(n%100));
    return w(n*1e-3|0) + ' thousand' + (n%1e3 === 0 ? '' : ' ' + w(n%1e3));
  };
  
  return w(n);
}