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

Use this code:

isNaN('geoff');

See isNaN() docs on MDN.

alert ( isNaN('abcd'));  // alerts true
alert ( isNaN('2.0'));  // alerts false
alert ( isNaN(2.0));  // alerts false