NaN === NaN is false in JavaScript
How to check for NaN when checking for a number in JavaScript
NaN is the only JavaScript value not equal to itself, so if you see a check for self-equality in JavaScript it is a NaN check, equivalent to Number.isNaN().
1 min readDec 5, 2019
Hi Jakub Szlapański, thanks for stopping by with your response to my article on how to check for JavaScript numbers!
You’re right, it seems like the following code checking for self-equality should always return true in JavaScript, since values should equal themselves.
The reality is that NaN (Not-A-Number) doesn’t follow that rule:
Indeed, I wrote about checking for NaN in Coding in Simple English:
I also have written about using Object.is() in JavaScript in Coding at Dawn:
Thanks again for sharing your response and helping me clarify this point!
