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isNaN() ↔ Instance Method returns boolean if Argument is NaN or not; applies Coercion

Number.isNaN does not apply Coercion and will only return true if Argument value is exactly NaN

NaN === NaN​

false

isNaN("string")​

true

Number.isNaN("string")​

false

Object.is(NaN, NaN)​

true

References​