What does isNaN function do? When is it used?

Question

I need to execute a function while mouse hover.But i want to execute only when mouse hover for over 2 or 3 seconds.Or else i don't want to execute the function.

Answer 1

NAN means not a number, it is used to check whether a value is number or not.

Example :
isNaN(123) -> it will return false.because it is a number
isNaN(12/3/2014)->it will return true.because it is not a number.