NaN and isNaN in JavaScript

The global property NaN represents any value that is Not A Number.
The global isNaN method allows you to check whether or not any value is Not A Number. The key point about using the isNaN( ) method is understanding that everything it tests is converted to a Number before the test is actually run.
Code GIST: gist.github.co...

[@MarstonH]

your calm, clarity, and experience is much appreciated

[@tranquiloteov]

You just saved me from a brain neurism. I've been reading the Mozilla documentation for half an hour and I didn't understand why it gave "false" with null or true. You explain great, I hope you make more videos. Thanks a lot.

[@salvadorgonzales5470]

Really enjoy your videos, your teaching style is just amazing.

[@SteveGriffith-Prof3ssorSt3v3]

Fuey Won Thanks!

[@Aprajita-mc8uy]

Thanks a lot. It really helped me as I was confused between Number.isNaN and isNan function.

[@rotrose7531]

Thank you very much, I hope someday my JS will get a little bit near the level you have mastered. I often get impressed by how many work you have done behind the scenes. Thank you.

[@williammansfield7471]

Gratitude. Saved me hours of agony.

[@dmytromoroz4451]

Splendid overview. Thanks a lot!

[@therealkayode]

Thank you. I am very grateful.

[@bsherrh4916]

Thank you, it was very useful

[@arzu300]

Thank you, now it all makes sense to me

[@chesterxp508]

Another very cool tutorial !!!

[@vrutishah3442]

Why does isNaN(" ") Returns false value? What is the logic behind the strings returning into false value?

[@SteveGriffith-Prof3ssorSt3v3]

It first tries to do a conversion of the value being passed in from whatever to number. If the conversion worked then it asks if that value is not a number. isNaN(" ") - false because Number(" ") == 0 which is a number isNaN("") - false because Number("") == 0 which is a number isNaN("hello") - true because Number("hello") == NaN ...

[@fivekncklshufl6146]

how would I check if an existing variable is equal to NaN?

[@alisabah9088]

thank u \

[@romeojoseph766]

what is the right way to check whether a value is a number data type or any other(without using regex)?

[@SteveGriffith-Prof3ssorSt3v3]

If you want to know if a value is a primitive value of type number, use the typeof operator

[@romeojoseph766]

@@SteveGriffith-Prof3ssorSt3v3 thanks for the information again!

[@yarik83men51]

Thx

[@rameshbhaip4732]

Can anyone explain this console.log(Number('hello')) // returns NaN console.log(Number.isNaN("hello")); // returns false

[@SteveGriffith-Prof3ssorSt3v3]

Number( ) - is taking a string value and trying to create a number from it. If the string cannot be interpreted as a number then the resulting value will be NaN (Not A Number). The isNaN( ) method takes a string and tests to see if the string is Not A Number.

[@rameshbhaip4732]

@@SteveGriffith-Prof3ssorSt3v3 then Number.isNaN("hello") should return true

[@SteveGriffith-Prof3ssorSt3v3]

@@rameshbhaip4732 yes

[@rameshbhaip4732]

@@SteveGriffith-Prof3ssorSt3v3 but it is returns false instead of true

[@JS-zm5se]

what will be output of IsNaN(NaN) and why?

[@SteveGriffith-Prof3ssorSt3v3]

The result would be true. isNaN( ) checks if the provided value is Not A Number. If you give it NaN, then it is, by definition, Not A Number. So, isNaN( ) will return true because NaN is not a number.

[@JS-zm5se]

@@SteveGriffith-Prof3ssorSt3v3 thank you

[@Thehealthycornerstore]

Do you know how to fix this when it appears in an ecommerce store? I'm at a loss, and I'm definitely not a programmer :/

[@SteveGriffith-Prof3ssorSt3v3]

Fix what? If there is a problem on your e-commerce store then you probably need a programmer to fix it.

[@Thehealthycornerstore]

Thanks, captain o.

[@SteveGriffith-Prof3ssorSt3v3]

I mean if it has to do with money, don't mess around with it. Hire a programmer who knows what they are doing.

[@kunjchoksi]

"let h" returns false!

[@SteveGriffith-Prof3ssorSt3v3]

Good catch. Yes. new Date() returns an integer timestamp... therefore false. Had I not been trying to finish the video quickly and had console logged out h then I would have corrected that. I have updated the code GIST with comments.

[@kunjchoksi]

thats fine :p