挑战优雅写法

function rgb2hex(sRGB) {
    if (!/^rgb\((\d{1,3},\s*){2}\d{1,3}\)$/.test(sRGB)) return sRGB;
    let  color = '#';
    sRGB.replace(/\d+/g, n => color += ('0' + (+n).toString(16)).slice(-2));
    return color;
}