The first only leaves the unique members of the list, so you get a sorted set. The second sorts lexicographically, because javascript's .sort() method on arrays sorts lexicographically. This means that if you have a list of numbers like [1, 2, 10], it will get sorted as [1, 10, 2]. Unless you pass your own comparator in.

What this page really demonstrates is that there is precisely one answer on stackoverflow containing a complete generic sort function in javascript (quicksort in fact).