Convert To Roman Number

roman-number.js

function romanNumber(num) {
    if (typeof num !== 'number') {
      return false;
    }

    let digits = String(+num).split("");
    let key = ["","C","CC","CCC","CD","D","DC","DCC","DCCC","CM","","X","XX","XXX","XL","L","LX","LXX","LXXX","XC","","I","II","III","IV","V","VI","VII","VIII","IX"];
    let romanNum = "";
    let i = 3;

    while (i--) {
      romanNum = (key[+digits.pop() + (i * 10)] || "") + romanNum;
    }

    return Array(+digits.join("") + 1).join("M") + romanNum;
  }