Lambda saysNaN is the only value not equal to itself — use Number.isNaN to detect it.
NaN === NaN is false, so you can't test for it with equality. Use Number.isNaN(x) (the global isNaN coerces and gives false positives). NaN propagates: any math with it yields NaN, so it often signals an earlier bad conversion you should trace back.
Power-ups you unlock
NaN !== NaN (unique in the language)
Detect with Number.isNaN(x)
Global isNaN coerces — avoid it
NaN propagates through math
The Mutator attacks — common mistakes
Testing x === NaN (always false)
Using global isNaN (false positives)
Ignoring a NaN that signals an upstream bug
Boss battleShow NaN !== NaN, then detect it correctly with Number.isNaN.