You can check yourself if a value is NaN

    // NaN typeof is ... number
    typeof value === 'number' && value != value

btw, the original isNaN() doesn't check if a value is NaN, it checks if a value is coercible to a number

    > isNaN("hello world")
    true

Ahh, that's clever. Overall I just don't want to tell people what variable names to use, even if they are obscure. At the very least the end developer can use the variable names for everything else other than NaN.