Roman Numerals

roman.js

const conversions = [
  [1000, 'M'],
  [900, 'CM'],
  [500, 'D'],
  [400, 'CD'],
  [100, 'C'],
  [90, 'XC'],
  [50, 'L'],
  [40, 'XL'],
  [10, 'X'],
  [9, 'IX'],
  [5, 'V'],
  [4, 'IV'],
  [1, 'I']
];

const convert = (arabian) => (
  conversions.reduce(([ roman, arabian ], [ value, text ]) => (
    [ roman + text.repeat(arabian / value), arabian % value ]
  ), [ '', arabian ])[0]
);