NaN is a number

Wednesday, June 28, 2006

JavaScript, like .NET, has a special thing called NaN, which stands for Not a Number. It is useful to determine if parsing a string successfully returned a number or for some operation results. Well, guess what this evaluates to:

typeof(Number.NaN)

Yes, you guessed it from the title, it evaluates to "number".

Just thought you might find this funny (as I did).

9 Comments

I know :|

Bertrand Le Roy - Thursday, June 29, 2006 10:07:50 PM

that's hilarious :-/

dave - Thursday, June 29, 2006 11:37:56 PM

Hi...

Thanks for ....

Can you give one more example of this in detail.

Mukesh

Mukesh - Friday, June 30, 2006 7:15:39 AM

It is wrong to be as amused as I am. And yet, I am. :)

Chris - Friday, June 30, 2006 3:20:24 PM

Not as silly as you think.
NaN is a property of the Number object. It is intended to be uses in comparisons, not as a value (object or not) of its own. You can think of it as a special form of Number or as a special type within the Number object. Number is really a helper object, mainly to deal with conversions to strings. So if you keep in mind that NaN is intended to be used -- by javascript -- as a test value for the function IsNaN, it perfectly makes sence.

EricW - Thursday, August 3, 2006 7:44:35 AM

Eric: sure, I was just pointing out that it's funny. Please notice that I didn't say it was stupid ;) but I wouldn't go so far as saying it "perfectly makes sense".

bleroy - Thursday, August 3, 2006 5:58:15 PM

NaN stands for Not-A-Number, but internally you can also assume it to be infinity. So 0/0 should churn out NaN

NoBuddy - Friday, September 4, 2009 7:50:09 AM

@NoBuddy: not exactly true. JavaScript actually has positive and negative infinities, which you can get by doing 1/0 or -1/0. 0/0 does give you NaN though because it can't determine the sign, but isNaN(1/0) returns false. So infinity is a number as far as JavaScript is concerned...

Bertrand Le Roy - Friday, September 4, 2009 3:34:11 PM

This may also make sense when considered from the standpoint of the floating-point standard.

Shawn T - Wednesday, October 27, 2010 11:01:19 PM

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