Returns a Boolean value that indicates whether a value is the reserved value NaN (not a number).
The isNaN function returns true if the value is NaN, and false otherwise. You typically use this function 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.