I don't understand why [0] doesn't return an optional that needs to be unwrapped?

Isn't [0] calling subscript(_:) (see https://developer.apple.com/documentation/swift/dictionary/subscript(_:)-8rfql

I think there might be something wrong with this kata on JavaScript. My code is passing the basic tests. While my code fails the attempt test on codewars, I put the exact same input into repljs.com (with the same random strarr and k that the test is testing) and it passes on repljs.com.

This has to be satire. Right?

Yeah I think that should still be validated. 0 is a valid value for UInt32 so it's still a potential bug. Negative numbers don't need to be checked though since they are not valid UInt32 values.

If anyone accidentally calls divisors(0) then this will crash. There needs to be a check like:

guard n != 0 else { return 0 }

However I'm not sure what you should return. Returning 0 would technically be right. 0 has 0 divisors since 0 can't be divided.