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

Try this code:

isNaN(parseFloat("geoff"))

For checking whether any value is NaN, instead of just numbers, see here: How do you test for NaN in Javascript?