OK, thanks, I wrote some comments and add a ramdom set of test to make it closer to the python version

Example test could be a little more helpful to match what is done in Python.

Your code is returning wrong values, check the last one. It seems you're ignoring uppercase letters.

I have these errors :

expected [ Array(15) ] to deeply equal [ Array(22) ]
expected [ 'ts', 'ai', 'az', 'fu', 'yg', 'q' ] to deeply equal [ Array(10) ]
expected [ 'bz', 'h', 'v', 'z' ] to deeply equal [ 'bz', 'Oh', 'EQ', 'Mv', 'Yz' ]

and I really don't understand what's happening because it's not what it is asked. Any clue someone ?