This solution seems to assume you can't refactor the Node class.

wow - this is the most pointless kata - really got annoyed with it.

ah nice, thanks!
yeah, understandability is definitely a valuable trait :-)

Despite your answer being more verbose and having more variables than most, I really liked your comments. Up

How does it work?

Your code is returning false always, and the test it fails is this:

Test.expect(isReallyNaN(NaN) === true)

That test expects true.

NaN doesn't exist as a data type. It's type is "number"

Please use a spoiler flag, comments are visible to everyone by default (I put the flag on for you this time). Also, format your code properly or it's not usable, see there: https://docs.codewars.com/training/troubleshooting/#post-discourse

LMGTFY

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That's how JavaScript works. This kata is just to show us this weird behavior. Btw he didn't consider null as numbers.

Typescript 3.3 or above should be enabled