Convert hexadecimal color to RGBA with transparency

hexadecimalToRGBA.ts

/** Converts hexadecimal color to RGBA with transparency. */
public transparentize(color: string, opacity: number = 0.5): string {
    return this.hexToRgbA(color, 1 - opacity);
}

/** Converts an hexadecimal color to RGBA */
public hexToRgbA(hex: string, opacity: number = 1): string {
    let c: any;
    if (/^#([A-Fa-f0-9]{3}){1,2}$/.test(hex)) {
        c = hex.substring(1).split('');
        if (c.length === 3) {
            c = [c[0], c[0], c[1], c[1], c[2], c[2]];
        }
        c = `0x${c.join('')}`;
        return `rgba(${[(c >> 16) & 255, (c >> 8) & 255, c & 255].join(',')}, ${opacity})`;
    }
    throw new Error('Bad Hex');
}