Number to / from roman numeral converter

1.readme.md

Created by Matthew, Daniel, Corey and Ray during JS Study Group: Algorithms.

Converts numbers to and from roman numerals, up to 3999.

There are more mathmetical solutions to the problem but this works.

2.roman.js

var input = [0, 1, 5, 1519, 3999]
var input2 = ["I", "VIII", "MMMCMXCIX", "IX", "V"]

definition = [
	[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"]
]

definition2 = {
	M: 1000,
	D: 500,
	C: 100,
	L: 50,
	X: 10,
	V: 5,
	I: 1
}

toRoman = function (input) {
	var _result = "";
	if (input === 0) {
		_result = "nulla"
	} else {
		for (var i = 0; i < definition.length; i++) {
			while (input >= definition[i][0]) {
				_result += definition[i][1];
				input -= definition[i][0];
			}
		}		
	}
	return _result;
}

toNum = function (input) {
	var _result = 0
	var _last = 0
	for (var i = input.length - 1; i >= 0; i--) {
		var num = definition2[input[i]]
		_result += num *  ((num < _last) ? -1 : 1);  // Brackets V. important.
		_last = num
	}
	return _result
}

// Main.
console.log("Roman Numerals to Numbers.");
for (var i = 0; i < input.length; i++) {		
	console.log(input2[i], "-->", toNum(input2[i]))
}
console.log("\n");
console.log("Numbers to Roman Numerals.");
for (var i = 0; i < input.length; i++) {		
	console.log(input[i], "-->", toRoman(input[i]))
}

3.output.md

Roman Numerals to Numbers.
I --> 1
VIII --> 8
MMMCMXCIX --> 3999
IX --> 9
V --> 5


Numbers to Roman Numerals.
0 '-->' 'nulla'
1 '-->' 'I'
5 '-->' 'V'
1519 '-->' 'MDXIX'
3999 '-->' 'MMMCMXCIX'