An extremely spare Roman numerals converter

roman.js

// No bounds/type checking
// No support for the overbar extension for numbers past 3999

const banks = [
	['', 'I', 'II', 'III', 'IV', 'V', 'VI', 'VII', 'VIII', 'IX'],
	['', 'X', 'XX', 'XXX', 'XL', 'L', 'LX', 'LXX', 'LXXX', 'XC'],
	['', 'C', 'CC', 'CCC', 'CD', 'D', 'DC', 'DCC', 'DCCC', 'CM'],
	['', 'M', 'MM', 'MMM']
]

export default number => number
	.toString()
	.split('')
	.map((digit, i, digits) => banks[digits.length - i - 1][digit])
	.join('')