isNaN Method
Returns a Boolean value that indicates whether a value is the reserved value NaN (not a number).
function isNaN(number : Number) : Boolean
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 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.
Show: