If you are going to reverse it wouldn't it be better to use tail which is more efficient?

getMiddle (reverse (tail (reverse (tail s))))

Or equivalently,

getMiddle . reverse . tail . reverse . tail $ s

Of course reverse . tail . reverse is just a less efficient (and stricter) init

getMiddle . init . tail $ s

interesting way of throwing errors!

I'm glad you enjoyed it! It is always good to find out it helps some one!

All katas here improved my skills, but this really made me learn a new feature in JS (something that didn't happen a long time).
Simple, short and super smart. Kudos!

Apology accepted :)