hexToRgba.js

const hexToRgb = hex => {
	// http://stackoverflow.com/a/5624139
	const shorthandRegex = /^#?([a-f\d])([a-f\d])([a-f\d])$/i
	hex = hex.replace(shorthandRegex, (m, r, g, b) => {
		return r + r + g + g + b + b
	})

	const result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex)
	return result
		? {
				r: parseInt(result[1], 16),
				g: parseInt(result[2], 16),
				b: parseInt(result[3], 16),
		  }
		: null
}

const rgba = (hex, alpha) => {
	const color = hexToRgb(hex)
	return `rgba(${color.r}, ${color.g}, ${color.b}, ${alpha})`
}

// background: ${rgba(color, 0.2)};