colorToRGBA.js

const colorToRGBA = (colorString, alpha) => {
    if (colorString.startsWith('rgb(')) {
        const rgb = colorString
            .slice(4, colorString.length - 1)
            .split(',')
            .map((item) => +item.trim());

        return `rgba(${rgb[0]}, ${rgb[1]}, ${rgb[2]}, ${alpha})`;
    }

    if (colorString.startsWith('#')) {
        const hex = [colorString.slice(1, 3), colorString.slice(3, 5), colorString.slice(5, 7)].map((item) =>
            parseInt(item, 16)
        );

        return `rgba(${hex[0]}, ${hex[1]}, ${hex[2]}, ${alpha})`;
    }

    return colorString;
};