Get the contrast ratio of two hex colors

contrast-ratio.js

const hex2Rgb = (hexString) => {
  const groups = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hexString);
  return groups
    ? [
        parseInt(result[1], 16),
        parseInt(result[2], 16),
        parseInt(result[3], 16),
      ]
    : null;
};

const getLuminanace = (hexString) => {
  const rgbValues = hex2rgb(hexString);
  const lightnessMap = rgbValues.map((v) => {
    const lightness = v / 255;
    return lightness <= 0.03928
      ? lightness / 12.92
      : ((lightness + 0.055) / 1.055) ** 2.4;
  });
  return Number(
    (
      0.2126 * lightnessMap[0] +
      0.7152 * lightnessMap[1] +
      0.0722 * lightnessMap[2]
    ).toFixed(3)
  );
};

const getContrastRatio = (colorA, colorB) => {
  const luminanceA = getLuminanace(colorA);
  const luminanceB = getLuminanace(colorB);

  return (
    (Math.max(luminanceA, luminanceB) + 0.05) /
    (Math.min(luminanceA, luminanceB) + 0.05)
  );
};