logis is easy...

Description already mentions this part: function should be case insensitive to pass the tests

Though, enforcement of Regex should not be done as this is an 8kyu kata (they can still learn the relevant technique by viewing other solutions)

This solution will work but if you leave the parameter as empty it will return false but i considered that the input should be boolean so its not a big deal tho

it won't cause an error and will return same res as yours, is it not?

very nice solution!

But they are not booleans

doesn check for null, undefined so on...

Fixed

I never decalre them unless they're needed.

You should, but it's not required. This way a function pollutes the global scope, and that's bad.

wow! Don't you have to declare const or let before the function expression name?

Fixed for JS.

In any case, this isn't the kata's problem so it's not an issue.