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

So I see several responses to this,

But I just use:

function isNaN(x){
     return x == x && typeof x == 'number';
}