Convert roman to arabic numerals

fromRomanNumerals.ts

const ROMAN_ARABIC_CONVERSION = {
  I: 1,
  V: 5,
  X: 10,
  L: 50,
  C: 100,
  D: 500,
  M: 1_000,
  V̅: 5_000,
  X̅: 10_000,
  L̅: 50_000,
  C̅: 100_000,
  D̅: 500_000,
  M̅: 1_000_000,
} as const;

type RomanSymbol = keyof typeof ROMAN_ARABIC_CONVERSION;

const segmenter = new Intl.Segmenter("en", { granularity: "grapheme" });

function split(str: string): string[] {
  return Array.from(segmenter.segment(str), ({ segment }) => segment);
}

function fromRomanNumerals(roman: string): number {
  const symbolList = split(roman);

  return symbolList.reduce<number>((total, sym, index) => {
    const currentValue = ROMAN_ARABIC_CONVERSION[sym as RomanSymbol];

    const nextValue =
      ROMAN_ARABIC_CONVERSION[symbolList[index + 1] as RomanSymbol] ?? 0;

    const value = nextValue > currentValue ? -currentValue : currentValue;

    return total + value;
  }, 0);
}

console.log(fromRomanNumerals("MCMLXXVII"));
console.log(fromRomanNumerals("IV"));
console.log(fromRomanNumerals("IX"));
console.log(fromRomanNumerals("XL"));
console.log(fromRomanNumerals("XC"));
console.log(fromRomanNumerals("CD"));
console.log(fromRomanNumerals("CM"));

console.log(fromRomanNumerals("V̅"));
console.log(fromRomanNumerals("X̅"));
console.log(fromRomanNumerals("L̅"));
console.log(fromRomanNumerals("C̅"));
console.log(fromRomanNumerals("D̅"));
console.log(fromRomanNumerals("M̅"));