Remove Duplicates from Array

var arr = [9, 9, 111, 2, 3, 4, 4, 5, 7];
var sorted_arr = arr.sort(); // You can define the comparing function here. JS default uses a crappy string compare.
var results = [];
for (var i = 0; i < arr.length - 1; i += 1) {
        if (sorted_arr[i + 1] == sorted_arr[i]) {
                results.push(sorted_arr[i]);
        }
}
 
alert(results);