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

Maybe also this:

function isNaNCustom(value){
    return value.toString() === 'NaN' && 
           typeof value !== 'string' && 
           typeof value === 'number'
}