Functional RGB to Hex Color

rbgToHexColor.js

const fixHex = v => v.length === 1 ? `0${v}` : v;

const decToHex = v => {
    return  fixHex(parseInt(v, 10).toString(16).toUpperCase());
};

// with map
const rgbToHexColor = function() {
    return [...arguments].map(decToHex).join('');
}

// with reduce
const rgbToHexColor2 = function() {
    return [...arguments].reduce((a, b) => a + decToHex(b), '');
}