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('geoff') == Number.NaN;

Answer 1

Hello,

you should use the global isNaN(value) function call.

• It is supported cross-browser
• See isNaN for documentation

Examples :

 isNaN('geoff'); // true
 isNaN('3'); // false

I hope this will help you.

Jerome Wagner

Answer 2

isNaN(parseFloat("geoff"))

Answer 3

Use

isNaN('geoff');

See isNaN

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