hexToRGBA

hexToRGBA.js

// https://stackoverflow.com/questions/15898740/how-to-convert-rgba-to-a-transparency-adjusted-hex

function hexify(color) {
  var values = color
    .replace(/rgba?\(/, '')
    .replace(/\)/, '')
    .replace(/[\s+]/g, '')
    .split(',');
  var a = parseFloat(values[3] || 1),
      r = Math.floor(a * parseInt(values[0]) + (1 - a) * 255),
      g = Math.floor(a * parseInt(values[1]) + (1 - a) * 255),
      b = Math.floor(a * parseInt(values[2]) + (1 - a) * 255);
  return "#" +
    ("0" + r.toString(16)).slice(-2) +
    ("0" + g.toString(16)).slice(-2) +
    ("0" + b.toString(16)).slice(-2);
}

let myHex = hexify('rgba(57,156,29,0.05)'); // "#f5faf3"

console.log(myHex);

function hexToRgb(hex) {
    let 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;
}

function hexToRGBA(hex, alpha) {
	let color = hexToRgb(hex);

	let r = Math.floor((color.r - 255 * (1 - alpha)) / alpha);
	let g = Math.floor((color.g - 255 * (1 - alpha)) / alpha);
	let b = Math.floor((color.b - 255 * (1 - alpha)) / alpha);

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

let myRGBA = hexToRGBA('#f5faf3', 0.05); // "rgba(55, 155, 15, 0.05)"

console.log(myRGBA);