Novel solution to the 'Convert Roman Numerals to Integers' kata...

fromRoman.js

String.prototype.fromRoman = function() {
  maps = new Object();
  maps["I"] = 1;
  maps["V"] = 5;
  maps["X"] = 10;
  maps["L"] = 50;
  maps["C"] = 100;
  maps["D"] = 500;
  maps["M"] = 1000;

  translateToValue = function(c){return maps[c];}
  
  next = 0
  negateSubtractedValues = function(digitValue){
    nextDigitValue = next;
    next = digitValue;
    return digitValue < nextDigitValue ? -digitValue : digitValue;
  }
  
  summing = function(a,b){return a + b;}

  return this
      .split("")
      .map(translateToValue)
      .reverse()
      .map(negateSubtractedValues)
      .reduce(summing,0);  
};

tests.js

var vows = require('vows'),
    assert = require('assert');

vows.describe('String').addBatch({
  'A string' : {
    'that`s empty': {
      topic: "", 
      'is roman for 0': function (topic) {
        assert.equal(topic.fromRoman(), 0);
      }      
    },
    'I': {
      topic: "I", 
      'is roman for 1': function (topic) {
        assert.equal(topic.fromRoman(), 1);
      }          
    },
    'II': {
      topic: "II", 
      'is roman for 2': function (topic) {
        assert.equal(topic.fromRoman(), 2);
      }          
    },
    'III': {
      topic: "III", 
      'is roman for 3': function (topic) {
        assert.equal(topic.fromRoman(), 3);
      }          
    },
    'IV': {
      topic: "IV", 
      'is roman for 4': function (topic) {
        assert.equal(topic.fromRoman(), 4);
      }          
    },
    'V': {
      topic: "V", 
      'is roman for 5': function (topic) {
        assert.equal(topic.fromRoman(), 5);
      }          
    },
    'VI': {
      topic: "VI", 
      'is roman for 6': function (topic) {
        assert.equal(topic.fromRoman(), 6);
      }          
    },
    'VII': {
      topic: "VII", 
      'is roman for 7': function (topic) {
        assert.equal(topic.fromRoman(), 7);
      }          
    },
    'VIII': {
      topic: "VIII", 
      'is roman for 8': function (topic) {
        assert.equal(topic.fromRoman(), 8);
      }          
    },
    'IX': {
      topic: "IX", 
      'is roman for 9': function (topic) {
        assert.equal(topic.fromRoman(), 9);
      }          
    },    
    'X': {
      topic: "X", 
      'is roman for 10': function (topic) {
        assert.equal(topic.fromRoman(), 10);
      }          
    },
    'XI': {
      topic: "XI", 
      'is roman for 11': function (topic) {
        assert.equal(topic.fromRoman(), 11);
      }          
    },
    'XII': {
      topic: "XII", 
      'is roman for 12': function (topic) {
        assert.equal(topic.fromRoman(), 12);
      }          
    },
    'XIII': {
      topic: "XIII", 
      'is roman for 13': function (topic) {
        assert.equal(topic.fromRoman(), 13);
      }          
    },
    'XIV': {
      topic: "XIV", 
      'is roman for 14': function (topic) {
        assert.equal(topic.fromRoman(), 14);
      }          
    },
    //...
    'XX': {
      topic: "XX", 
      'is roman for 20': function (topic) {
        assert.equal(topic.fromRoman(), 20);
      }          
    },
    // ...
    'L': {
      topic: "L", 
      'is roman for 50': function (topic) {
        assert.equal(topic.fromRoman(), 50);
      }          
    },
    'XC': {
      topic: "XC", 
      'is roman for 90': function (topic) {
        assert.equal(topic.fromRoman(), 90);
      }          
    },
    'XCIX': {
      topic: "XCIX", 
      'is roman for 99': function (topic) {
        assert.equal(topic.fromRoman(), 99);
      }          
    },
    
  }
}).export(module)