A function that takes in a number from 1 to 1000 and returns that number in Roman Numerals.

to-romans.js

Number.prototype.toRomans = function () {
    let result = ""
    for (let [i, alpha] of [...this.toString()].reverse().entries()) {
        let set = ""
        if (alpha > 0 && alpha <= 4) set += "IXCM"[i].repeat((alpha - 1) % 3 + 1)
        if (alpha > 3 && alpha <  9) set += "VLD"[i]
        if (alpha > 5 && alpha <= 9) set += "IXC"[i].repeat(alpha % 3 + 1)
        if (alpha === "9") set += "XCM"[i]
        result = set + result
    }
    return result
}