Array.prototype.getDuplicates = function () { var duplicates = {}; for (var i = 0; i < this.length; i++) { if(duplicates.hasOwnProperty(this[i])) { duplicates[this[i]].push(i); } else if (this.lastIndexOf(this[i]) !== i) { duplicates[this[i]] = [i]; } } return duplicates; };