https://strangepaths.com/wp-content/plugins/gengo/js/gengo_common.js

1Array.prototype.in_array = function(search_term)
2{
3  var i = this.length;
4	do
5	{
6		if (this[i] === search_term) return true;
7	} while (i--);
8  return false;
9}
10
11// Returns all the elements of second_array that are not in this array.
12Array.prototype.diff = function(second_array) {
13  var return_array = Array();
14	var i = second_array.length;
15	var j = 0;
16	do {
17		if (!this.in_array(second_array[i])) {
18			return_array[j++] = second_array[i];
19		}
20	} while (i--)
21	return return_array;
22}