get proper text color for given background color (even with true-background color for transparency background)

getProperColor.js

export function properTextColor(backColor, trueBackColor) {
  function getRGBAfromHEX(color) {
    color = color.slice(1).replace(color.length < 5 && /./g, '$&$&');
    color = parseInt(color.length > 6 ? color : color + 'FF', 16);

    return {
      r: color >>> 24,
      g: color >>> 16 & 255,
      b: color >>>  8 & 255,
      a: color & 255
    };
  }

  function getHSPfromRGB(r, g, b) {
    return Math.sqrt(0.299 * (r * r) + 0.587 * (g * g) + 0.114 * (b * b));
  }

  let c = getRGBAfromHEX(backColor);
  let b = getRGBAfromHEX(trueBackColor || '#FFFFFF');
  Array.from('rgb').forEach(_ => {c[_] = (c[_] * c.a + b[_] * (255 - c.a)) / 255});

  return (getHSPfromRGB(c.r, c.g, c.b) > 160) ? '#000000' : '#FFFFFF';
}