Determine font color based on the background color

background-color.js

// suppose background color is: rbg(0, 23, 255)
function textColorBasedOnBackground(backgroundColor) {
  backgroundColor = backgroundColor.substring(1);
  const r = parseInt(backgroundColor.substring(0,2), 16); // 0 ~ 255
  const g = parseInt(backgroundColor.substring(2,4), 16);
  const b = parseInt(backgroundColor.substring(4,6), 16);

  const srgb = [r / 255, g / 255, b / 255];
  const x = srgb.map((i) => {
    if (i <= 0.04045) {
      return i / 12.92;
    } else {
      return Math.pow((i + 0.055) / 1.055, 2.4);
    }
  });

  const L = 0.2126 * x[0] + 0.7152 * x[1] + 0.0722 * x[2];
  return L > 0.179 ? "#000" : "#fff";
}

const backgroundColor = "rbg(0, 23, 255)";
const textColor = textColorBasedOnBackground(backgroundColor); // #fff