Determine best contrast color (black/white) for a given color

ContrastingColor.js

function hexToRgb(hex) {
    var result = /^#?([a-f\d]{2})([a-f\d]{2})([a-f\d]{2})$/i.exec(hex);
    return result ? {
        r: parseInt(result[1], 16),
        g: parseInt(result[2], 16),
        b: parseInt(result[3], 16)
    } : null;
}

function contrastColor(color) {
    var rgb = hexToRgb(color);
    var r = rgb.r * 255,
    g = rgb.g * 255,
    b = rgb.b * 255;
  var yiq = (r * 299 + g * 587 + b * 114) / 1000;
  return (yiq >= 128) ? '#111' : '#fff';
}