Reading is a lost art ..

Sorry I could only upvote your comment once Cito.

really nicer and more readable, yes. :)

Still prefer the one-liner, especially the new version with fat arrows: http://www.codewars.com/kata/reviews/54be2a15518b8dcff90001f2/groups/56fc240e4504004e510009dd

It's less readable because you put the function decs on new lines, which I've never seen before and don't think anybody actually does. The code itself is still not great as using arbitrary names such as "v" and "w" don't give you any hints about what the code actually does.

Also, best practice should definitely include how the code is presented. Code that can be passed around from colleage to colleage and be quickly understood by everyone should be something you're looking to achieve, i.e. it should be part of the best practice.

I saw your link. Below a small part of what I got with trying once more:

Random Testing mxdiflg:
[] , [ 'aa', 'yymmmmbbll', 'iiiiqhhhhgggssw', 'xxhhiiittuu', 'bbzz', 'ssmdddyy', 'nnlll' ]
Test Passed: Value == -1

Random Testing mxdiflg:
[ 'wwffqqqaammmmfffss', 'fffffkknn', 'ddlllqquuwwwwccaaah' ] , []
Test Passed: Value == -1

Random Testing mxdiflg:
[ 'xoofffqq', 'gsssfftsssseeeettt', 'gggxxxxmmmmmsssppeeeeekkkhhhbbkk' ], []
Test Passed: Value == -1

Random Testing mxdiflg:
[], [ 'ooollkkkkhhhh', 'qqqqeljjffbooobbb', 'v' ]
Test Passed: Value == -1

I repeat myself:

the expected result is -1 when at least one of the arrays is empty.

I tested the random tests too as everybody passing the kata did and I had verified that a test returns -1 in this case.
I don't understand why you got 26.
The "solution" in the random tests returns -1 for the example you gave in your previous post:
[ 'ttffdddooo', 'bbbtttthhhnnnny', 'hhkkkww', 'jlllh', 'jjccccaaaazzzztttqqqwwqqqq' ] [] --> -1

Sorry of not having answered sooner but I just saw your post. If it is JS, 55 CW passed the kata without problem. I tried the kata once more and the expected result is -1 when one of the arrays is empty.

Doy, you're right. I was thinking insensitive in the sense that it doesn't matter what case you use, always go with what's in the key. I've updated the description.

I'd name such soluion case-sensitive

I never really used Twitter, but I'm kind of sad that Jaden deleted all of his tweets. Meanwhile, I actually find my Whitespace Interpreter kata to be better than this one.

The solution is case-insensitive. If the key doesn't specify an uppercase letter, then you don't apply any transformation to an uppercase letter.

Refer to the last bulletpoint in the description.

Actually not: the Haskell code properly awaits for them to be equal: what error message did you get, specifically?

Same bug in Haskell.