yiq formula to define black or white text for maximum contrast automatically

js.js

var textColor = function (bgColor) {
  var r = bgColor.r * 255,
      g = bgColor.g * 255,
      b = bgColor.b * 255;
  var yiq = (r * 299 + g * 587 + b * 114) / 1000;
  return (yiq >= 128) ? 'black' : 'white';
}