Convert roman numerals to numerals using recursive solution

romanNumeralToNumeral.js

  /**
   *
   * @param {Strig} roman roman numeral like
   * @throws {RangeError} if roman is not a valid roman numeral
   * @returns Number
   */
  function romanNumeralToNumeral (roman = '') {
    if (!roman.match(/^[IVXLCDM]+$/)) {
      throw new RangeError('Invalid roman numeral')
    }

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

    const converter = (curIndex = 0, result = 0) => {
      if (roman.length > curIndex) {
        const current = roman[curIndex]
        const next = roman[curIndex + 1]

        const nextResult = romanToNumeralPairs[current] < romanToNumeralPairs[next] ? result - romanToNumeralPairs[current] : result + romanToNumeralPairs[current]

        return converter(curIndex + 1, nextResult)
      }

      return result
    }

    return converter()
  }