indexof javascript duplicate arrays
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;
};