convert_to_roman.js

const convertToRoman = num => {
  const roman = [...'IVXLCDM'];
  const patt = [
    [],
    [0],
    [0, 0],
    [0, 0, 0],
    [0, 1],
    [1],
    [1, 0],
    [1, 0, 0],
    [1, 0, 0, 0],
    [0, 2]
  ];
  return [...(num+'')].map((n,i,a)=>patt[n].map(r=>roman[(a.length-1-i)*2+r]).join``).join``;
  };