gistfile1.js

/*
  Script that darken a hex color.
  
  Released under the MIT license
  
  Junya Ishihara <junya@champierre.com>
  http://champierre.com
*/

function darken(hexstr, scalefactor) {
  var r = scalefactor;
  var a, i;
  if (typeof(hexstr) != 'string') {
    return hexstr;
  }
  hexstr = hexstr.replace(/[^0-9a-f]+/ig, '');
  if (hexstr.length == 3) {
    a = hexstr.split('');
  } else if (hexstr.length == 6) {
    a = hexstr.match(/(\w{2})/g);
  } else {
    return hexstr;
  }
  for (i=0; i<a.length; i++) {
    if (a[i].length == 2)
      a[i] = parseInt(a[i], 16);
    else {
      a[i] = parseInt(a[i], 16);
      a[i] = a[i]*16 + a[i];
    }
  }

  var maxColor = parseInt('ff', 16);

  function _darken(a) {
    return a * r;
  }

  for (i=0; i<a.length; i++) {
    a[i] = _darken(a[i]);
    a[i] = Math.floor(a[i]).toString(16);
    if (a[i].length == 1) {
      a[i] = '0' + a[i];
    }
  }
  return a.join('');
}