isNaN Method (Windows Scripting - JScript)
Returns a Boolean value that indicates whether a value is the reserved value NaN (not a number).
The required numValue is the value to be tested against NaN.
You typically use this method to test return values from the parseInt and parseFloat methods.
Alternatively, a variable that contains NaN or another value could be compared to itself. If it compares as unequal, it is NaN. This is because NaN is the only value that is not equal to itself.