NaN is a special case. A number is NaN only if it’s NaN or if it’s a division of 0 by 0 expression, which returns NaN. In all the other cases, we can pass it what we want but it will return false:

Number.isNaN(NaN) //true
Number.isNaN(0 / 0) //true

Number.isNaN(1) //false
Number.isNaN('Flavio') //false
Number.isNaN(true) //false
Number.isNaN({}) //false
Number.isNaN([1, 2, 3]) //false