This week’s scala kata is a favorite I’ve implemented before in javascript, Solitaire Cipher which was featured some time back as the first problem on the Ruby Quiz site.
I think there should be enough source material on those two links to get started. The true acid test is being able to shuffle a deck of cards, encrypt a message, and then decrypt it using the deck. Bonus points if you can send people encrypted messages that they can decrypt on their machine using your program. 
[...] Last week’s scala kata was a bit challenging as it required a bit more advanced scala knowledge than the katas I’ve done so far. Breaking from last week I’ve decided to head back to the basics and dream up a kata to help focus on some of scala’s language features versus a full blown program. [...]