decimalToRoman.js

const Units = {
  one: 'I',
  five: 'V',
  ten: 'X',
  fifty: 'L',
  hundred: 'C',
  fiveHundred: 'D',
  thousand: 'M',
}

function detemineBaseUnitOutput(baseUnit: string, val: number) {
  return Array(val).fill(baseUnit).join('');
}

function handleUnit(baseUnit: string, midUnit: string, nextBaseUnit: string, val: number) {
  let parsedVal;
  
  if (!val) {
    parsedVal = '';
  } else if (val < 4) {
    parsedVal = detemineBaseUnitOutput(baseUnit, val);
  } else if (val === 4) {
    parsedVal = baseUnit + midUnit;
  } else if (val < 9) {
    parsedVal = midUnit + detemineBaseUnitOutput(baseUnit, val - 5);
  } else {
    parsedVal = baseUnit + nextBaseUnit;
  }
  
  console.log(val, parsedVal)
  
  return parsedVal;
}

function handleOnes(val: number) {
  return handleUnit(Units.one, Units.five, Units.ten, val);
}

function handleTens(val: number) {
  return handleUnit(Units.ten, Units.fifty, Units.hundred, val);
}

function handleHundreds(val: number) {
  return handleUnit(Units.hundred, Units.fiveHundred, Units.thousand, val);
}

function handleThousands(val: number) {
  return detemineBaseUnitOutput(Units.thousand, val);
}

const BaseTenUnitHandler = {
  '1': handleOnes,
  '2': handleTens,
  '3': handleHundreds,
  '4': handleThousands,
}

export function solution(number: number): string {
  // convert the number to a roman numeral
  const units = number.toString().split('');
  const unitsLength = units.length;
  let unitsIter = unitsLength;
  let romanNumerals = [];
 
  while (0 < unitsIter--) {
    const valueToParse = units[unitsIter];
    const valueParser = BaseTenUnitHandler[unitsLength - unitsIter];
    
    romanNumerals.unshift(valueParser(parseInt(valueToParse)));
  }
  
  return romanNumerals.join('');
}