javascript - Is NaN falsy? Why NaN === false returns false

Question

1. Why NaN === false => false, isn't NaN falsy?
2. Why NaN === NaN => false, but !!NaN === !!NaN => true

I've been racking my brain trying to figure this out.

Answer 1

1. Falsy and being strictly equal to false are very different things, that's why one has a y instead of an e. ;)
2. NaN is spec'd to never be equal to anything. The second part of your question is comparing false === false, which is funnily enough, true :)

If you really want to know if something is NaN, you can use Object.is(). Running Object.is(NaN, NaN) returns true.