Convert decimal RGB values to HTML hex string

rgb2hex.ts

// prepend a character to a string for a given result string length
const prependCharToLength = (str: string, char: string = '0', len: number = 2): string => {
    let r: string[] = [];
    let s: string[] = str.split('');
    for (let i: number = len - 1; i >= 0; i--) {
        r[i] = (s.length - i > 0) ? s[i] : char;
    }
    return r.join('');
};

// convert decimal color rgb values to html hex color string
const convertColorsToHex = (r: number, g: number, b: number): string => `#${
    prependCharToLength(r.toString(16))}${
    prependCharToLength(g.toString(16))}${
    prependCharToLength(b.toString(16))}`;