Thanks for the help. I will annotate it for future katas.

Try submitting your solution again, I've fixed the issue.
I added a shuffle function to Array's prototype, so your for(..in..) was trying to add that function to your total variable, resulting in NaN

In my test fixture I added a function on the Array prototype to shuffle the elements in an array. The for(..in..) loop you're using is trying to add that function to your solution variable, causing it to be NaN. I can't modify the test fixture anymore, so you'll have to modify your code. Switching the for(..in..) to a for(var i=0; i<aux.length; i++){..} should do the trick

Can you post a code snippet and mark it as a spoiler?

When I clicked in "Save & Attempt" i got the following output:
Test Failed: Expected: abcdefhijklmoprtvwxy, instead got: abcdefhijklmoprtvwxyfunction (){ var copy = [].concat(this); var ran1, ran2, tmp; for(var i=0; i

And that is not in my code.