Q:

Improve Regex to match duplicates in a list

I am using a regex to find dupliates in a list. It is only a short comma seperated list, and performance is not an issue, so there is no need to tell me I should not use regex for those reasons.
// returns a match because some is repeated
"some,thing,here,some,whatever".match(/(^|,)(.+?)(,|,.+,)\2(,|$)/g)

Questions...

Can this regex be improved?
Does it cover all possible scenarios where comma is not in the seperated strings
Is there a better (preferably more readable and more efficient) way to do this?

A:

I don't see the purpose of using regexes here, unless you like unimaginable pain. If I had to find duplicates I would

Obtain an array of words
var words = "...".split(',');

optionally lowercase everything, if you feel like doing that
sort the array
words.sort()

Duplicates should now all be in consecutive positions of the array.

As an extra advantage, I`m pretty sure this would be vastly more efficient than a regex version.

