array prototype functions that i use

prototype_array.js

Array.prototype.unique = function() { return this.filter(function(val, idx) { return this.indexOf(val) === idx; }, this); };
Array.prototype.union = function(that) { return this.concat(that).unique(); };
Array.prototype.intersection = function(that) { return this.filter(function(val) { return that.indexOf(val) !== -1; }).unique(); };
Array.prototype.difference = function(that) { return this.filter(function(val) { return that.indexOf(val) === -1; }).unique(); };