How do you think I can improve this?

It's not optimized and not clever solution.

Not working

Well I prefer to create two separate functions instead of one but bigger. First one - capitalizeFirstLetter(string) and second one which uses it while mapping. That makes it more clear in my opinion.

Very creative! =)

I too submitted a solution that didn't work for irregular subtractive expressions (such as "MCDXLIII").

Agreed and also going in the high numbers - I had errors initially in my code that the test didn't catch.

Needs more tests just like: IV, IX, CXIX...

Nice solution .

Hi, anyone can help to find my mistake?
I do get:
page_index returned incorrect value when provided a item_index argument that was out of range: 2 should equal -1

But can't reproduce the error with my test cases.
Thank you.

js test wasn't made