Calculate the minimum shade or tint of a color in order to get a W3C compliant contrast between them

minimum-contrast.js

// https://www.w3.org/TR/UNDERSTANDING-WCAG20/visual-audio-contrast-contrast.html

function getMinContrastColor(rgb, isLargeFont) {
  const minContrastRatio = isLargeFont ? 3.0 : 4.5;
  let contrastIsDark = isContrastDark(rgb);
  let i = 0.01;
  let contrastRgb = [];
  let contrastRatio = 0;
  while (contrastRatio < minContrastRatio && i < 1) {
    contrastRgb = calculateGradient(rgb, contrastIsDark, i);
    contrastRatio = getContrastRatio(rgb, contrastRgb, contrastIsDark);
    i += 0.01;
  }
  return contrastRgb;
}

function getContrastRatio(rgb1, rgb2, isDark) {
  return isDark
    ? (getLuminance(rgb1) + 0.05) / (getLuminance(rgb2) + 0.05)
    : (getLuminance(rgb2) + 0.05) / (getLuminance(rgb1) + 0.05);
};

function isContrastDark(rgb) {
  const isDark = getLuminance(rgb) > Math.sqrt(1.05 * 0.05) - 0.05; // ~= 0.179
  return isDark;
}

function getLuminance(rgb) {
  const lumRgb = rgb.map(el => {
    el = el / 255.000;
    return el <= 0.03928 ? el / 12.92 : ((el+0.055)/1.055) ** 2.4;
  });
  return 0.2126 * lumRgb[0] + 0.7152 * lumRgb[1] + 0.0722 * lumRgb[2];
}

function calculateGradient(rgb, isDark, opacity) {
  return rgb.map(val =>
    calculateIndividualColor(val, isDark ? 0 : 255, opacity)
  );
};

function calculateIndividualColor(color, bColor, opacity) {
  return Math.round(opacity * bColor + (1 - opacity) * color);
}