Groups | Search | Server Info | Keyboard shortcuts | Login | Register [http] [https] [nntp] [nntps]

Groups > comp.lang.javascript > #20559

Re: falsy and truthy

Show all headers | View raw

On Fri, 05 Jul 2013 20:01:38 -0700, tlbaxter99 wrote:

> Hi everyone,
> 
> I thought I understood falsy and truthy until I ran this code:
> 
> var falsyValues = [false, 0, null, "", undefined, NaN];
> 
> for (var index in falsyValues)
>    if (!falsyValues[index])
>       console.log("FALSE");
>    else
>       console.log("TRUE");
> 
> As I expected, "FALSE" was printed for all 6 values. No problem.
> 
> Now, when I modify the if() statement to this:
>    if (false == falsyValues[index])
> 
> I see that null, undefined and NaN do NOT compare as being equal to
> false, yet when using the not operator(!) a shown earlier, they ARE
> considered false.
> 
> Can someone explain this? Using the not operator (!) is apparently not
> the same as comparing directly against false.

falsy and false are two different things.

falsy values are never truthy, but that doesn't mean they're always false.

Languages may have pseudo-values or named constants or whatever else you 
want to call them which are never == anything else, even themselves, but 
are still considered falsy.

-- 
Denis McMahon, denismfmcmahon@gmail.com

Back to comp.lang.javascript | Previous | Next — Previous in thread | Next in thread | Find similar | Unroll thread

Thread

falsy and truthy tlbaxter99@yahoo.com - 2013-07-05 20:01 -0700
  Re: falsy and truthy Denis McMahon <denismfmcmahon@gmail.com> - 2013-07-06 07:20 +0000
  Re: falsy and truthy Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-07-06 10:24 +0200
    Re: falsy and truthy "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-07-06 11:22 +0200
  Re: falsy and truthy "Joao Rodrigues (J.R.)" <groups_jr-1@yahoo.com.br> - 2013-08-10 09:03 -0300

csiph-web