GenerateRandomColor.js

function generateRandomColor(userConfig = {}) {
    const defaultConfig = {
        r: [0, 255],
        g: [0, 255],
        b: [0, 255],
        a: [1, 1],
    }
    const config = Object.assign({}, defaultConfig, userConfig);

    let { r, g, b, a } = config;

    let [minR, maxR] = r;
    let [minG, maxG] = g;
    let [minB, maxB] = b;
    let [minA, maxA] = a;

    maxA *= 1000;
    minA *= 1000;

    r = randomIntFromInterval(minR, maxR);
    g = randomIntFromInterval(minG, maxG);
    b = randomIntFromInterval(minB, maxB);
    a = randomIntFromInterval(minA, maxA) / 1000;

    return `rgba(${r}, ${g}, ${b}, ${a})`;
}