function array_diff_ukey (arr1) {
  // http://kevin.vanzonneveld.net
  // +   original by: Brett Zamir (http://brett-zamir.me)
  // *     example 1: $array1 = {blue: 1, red: 2, green: 3, purple: 4}
  // *     example 1: $array2 = {green: 5, blue: 6, yellow: 7, cyan: 8}
  // *     example 1: array_diff_ukey($array1, $array2, function (key1, key2){ return (key1 == key2 ? 0 : (key1 > key2 ? 1 : -1)); });
  // *     returns 1: {red: 2, purple: 4}
  var retArr = {},
    arglm1 = arguments.length - 1,
    cb = arguments[arglm1],
    arr = {},
    i = 1,
    k1 = '',
    k = '';

  cb = (typeof cb === 'string') ? this.window[cb] : (Object.prototype.toString.call(cb) === '[object Array]') ? this.window[cb[0]][cb[1]] : cb;

  arr1keys: for (k1 in arr1) {
    for (i = 1; i < arglm1; i++) {
      arr = arguments[i];
      for (k in arr) {
        if (cb(k, k1) === 0) {
          // If it reaches here, it was found in at least one array, so try next value
          continue arr1keys;
        }
      }
      retArr[k1] = arr1[k1];
    }
  }

  return retArr;
}

$array1 = {blue: 1, red: 2, green: 3, purple: 4}
$array2 = {green: 5, blue: 6, yellow: 7, cyan: 8}
array_diff_ukey($array1, $array2, function (key1, key2){ return (key1 == key2 ? 0 : (key1 > key2 ? 1 : -1)); });

{red: 2, purple: 4}