How do you check that a number is NaN in JavaScript?

Question

I’ve only been trying it in Firefox’s JavaScript console, but neither of the following statements return true:

parseFloat(\'geoff\') == NaN;

parseFloat(\'ge         


        

Answer 1

I use underscore's isNaN function because in JavaScript:

isNaN(undefined) 
-> true

At the least, be aware of that gotcha.