Navigator 3.0

Number.NaN

`Number.NaN` is a special value that indicates that
the result of some arithmetic operation (such as division by
zero) or mathematical function is "Not-a-Number."
`parseInt()` and `parseFloat()` return this
value when they cannot parse the specified string, and you
might use `Number.NaN` in a similar way to indicate an
error condition for some function that normally returns a
valid number.

JavaScript prints the `Number.NaN` value as
`NaN`. Note that the `NaN` value
always compares unequal to any other number, including
`NaN` itself. Thus, you cannot check for the
Not-a-Number value by comparing to `Number.NaN.` Use
the `isNaN()` function instead.