RunKit + npm: roman2int

const roman2int = require("roman2int") const romanNumbers = [ "", "III", "IV", "VIII", "IX", "X", "XV", "XXVIII", "LXIX", "XCIX", "XLIX", "MDCCXCVIII", "MCMLII", "MMDCCCLXXXIII", "MDCCCLXXXII", "MMDCCCLXIII", "XD", "MMMDLXI", "MMMDCCCLXVIII", "MMDCCCLXIX", "MDCCCLXVI", "iii", "MMDCXXXIX", "MMMCLXVII", "MMMDCCXLVII", "0" ]; let numbersMap = []; romanNumbers.forEach((romanNumber, index) => { const intNumber = roman2int(romanNumber); typeof intNumber === "number" ? numbersMap.push({ roman: romanNumber, arabic: intNumber }) : console.log(`Pass# ${index}, Roman numeral: ${romanNumber}, roman2int error: ${intNumber}`); }); console.log(numbersMap);