Not enough tests. Look at the solutions ?!

Duplicate.

any datatype

but RegExp, Date, Set and Map are not tested. ( Are null and undefined? I didn't check that thoroughly. )

"!" is object keys is to be disregarded, apparently, but this is not specified.

Relying on random tests only is not good. Have fixed tests for edge cases. ( No, I don't know all edge cases. Get creative, solvers might too. )

All the basic katas solvable with a plain map, filter, or reduce (or any weird combination of these) lack novelty, and have practically zero value.

No, seriously, these katas are absolutely trash:

• the sample tests are wrong
• the possible inputs are not mentioned
• the task lacks any novelty
• your solution is designed specifically to pass the tests you've written, and any changes to the environment would break everything (but that's just me ranting that you're a noob who can't code properly but dove into a far more complex domain than that)

Do every one a favor, and just stop. I don't know whether you're a student or a representative of this "Ironhack" bootcamp/organization/scam, but your attempts at creating katas are terrible. And if this low-quality spam continues, you will only end up being reported.

Implement a function which returns a single possible value

This task is plain trash, and should be retired.