@shotah

All input strings will be nonempty, and will only consist of parentheses, brackets and curly braces: ()[]{}.

This is not cheating. Those people just solve the kata, with a code that passes the tests. This is what CodeWars is all about. The one(s) to blame are the author(s) of the kata and/or the translations who provided incomplete tests. And to clarify: I did not check whether what you say is correct or not about invalid codes.

See this

they require Node 12, it's not a kata issue (codewars support up to Node 12 but javascript tests cannot be edited for this kata :/ )

Your code's problem. Nobody said year is limited to 4 digits.