haha, well played.

I can only figure out how to complete it in 26 chars ;_;

There are no tests to enforce that condition however.
Most of the passing solutions remove uppercase vowels...

My solution was an intentional cheat, in that it won't work if the username starts with a number.
So my solution would return false for '123abc' even though that is a valid username according to guidelines.

Recommend adding '123abc' and '1abcde' to fixed tests.
Looking forward to having to resubmit a correct username validation :P

Array.map(fn) executes a function on each item in an array and returns a new array of the transformed items.
more info on Array map here

x => doThing(x) is (practically) the same as function(x) { return doThing(x) }
more info on Arrow functions here

Marked as ready!

Your first example test

Test.assertSimilar(imageFilter("favicon.gif"), ..etc)

passes a string not an array, so everyone is checking if arr param is an array or not. I figure this is a typo because the test cases only pass arrays & your own solution expects an array (and fails the example tests).

Please fix the example tests.

Ahh foolish me, I spread the string to an array even though it's an iterable to begin with.

Second JS test case should be assertEquals not assertEqual. Throws an error since the method doesn't exist.

Nicely fleshed out example tests, well done.

My favourite thing about this kata is seeing which hashtag people decided to use for their solution :)

Uhh... forked myself since there's so little documentation on kumite/forks.
What's the protocol for refining your own solution(s)?

Should you 'train again' and submit a new solution,
'discuss'-> comment on your own solution,
or fork your own solution like I have here?