OP solved it, closing.

Just array. You are overthinking it.

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map() is Array method, you are trying to use it with number.

It's just recursion, first return calls the same function while changing the argument, but in this case it looks redundant, you can achieve same results with simple loop. Second return just returns value when you reached your condition and don't need to make more calls.

1. Issue tag is for the issues with a kata, such as broken test cases, incorrect descriptions etc. Next time please post a Question.
2. Without you posting your code with a spoiler flag, it is a guesswork to try to help you. Looking how there is no performance tag and my first naive solution passed in 2500 ms, my guess is you got infinite loop somewhere in your code.

256 in binary form is 100000000. When you place "ab" in the end as in example, all is mitigated by 0's. 32 is 100000, so you actually will get 6th letter from the end of "ctmdpt", which is "c".

The function accepts an integer and returns an integer.

returns

Your code always returns value after first iteration. You can easily see that if you add one print().

It's a linker error. It looks like default function name is digitize and that name is used in preloaded code for tests, linker can't find it. Most likely you changed the name of the function.

We will consider a, e, i, o, u as vowels for this Kata (but not y).

Look here for code formatting.

For all we know user can enter 1000000. But kata got clear constraints 1 <= month <= 12.