bootstrap_styles-1.0.x-dev/js/components/yiq.js

// Function to convert hex format to a rgb color
function rgb2hex(orig) {
  var rgb = orig.replace(/\s/g, '').match(/^rgba?\((\d+),(\d+),(\d+)/i);
  return (rgb && rgb.length === 4) ? "#" +
    ("0" + parseInt(rgb[1], 10).toString(16)).slice(-2) +
    ("0" + parseInt(rgb[2], 10).toString(16)).slice(-2) +
    ("0" + parseInt(rgb[3], 10).toString(16)).slice(-2) : orig;
}

/*!
 * Get the contrasting color for any hex color
 * (c) 2019 Chris Ferdinandi, MIT License, https://gomakethings.com
 * Derived from work by Brian Suda, https://24ways.org/2010/calculating-color-contrast/
 * @param  {String} A hexcolor value
 * @return {String} The contrasting color (black or white)
 */
var getContrast = function (hexcolor) {
  // If a leading # is provided, remove it
  if (hexcolor.slice(0, 1) === '#') {
    hexcolor = hexcolor.slice(1);
  }

  // If a three-character hexcode, make six-character
  if (hexcolor.length === 3) {
    hexcolor = hexcolor.split('').map(function (hex) {
      return hex + hex;
    }).join('');
  }

  // Convert to RGB value
  var r = parseInt(hexcolor.substr(0, 2), 16);
  var g = parseInt(hexcolor.substr(2, 2), 16);
  var b = parseInt(hexcolor.substr(4, 2), 16);

  // Get YIQ ratio
  var yiq = ((r * 299) + (g * 587) + (b * 114)) / 1000;

  // Check contrast
  return (yiq >= 128) ? 'dark' : 'light';
};