Re: Difference between == and ===?

From	"Jukka K. Korpela" <jkorpela@cs.tut.fi>
Newsgroups	comp.lang.javascript
Subject	Re: Difference between == and ===?
Date	2012-06-06 07:55 +0300
Organization	A noiseless patient Spider
Message-ID	<jqmnsi$3qt$1@dont-email.me> (permalink)
References	(16 earlier) <PjNch1HDZQzPFw9$@invalid.uk.co.demon.merlyn.invalid> <jql7em$9d0$1@news.albasani.net> <XnsA069CD919A8F5eejj99@194.109.133.133> <jqmf33$hre$1@news.albasani.net> <jqmi38$d3m$1@dont-email.me>

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2012-06-06 6:16, Norman Peelman wrote:

> NULL is not an object, nor can it represent one.

"NULL" is an identifier with no meaning assigned to it in JavaScript 
definition (ECMAScript standard).

>>> "null" means a variable is not filled
>>> with an allowed type value.
>>>
>
> NULL does not define a type. NULL is nothing.

"NULL" is anything you define it to be in your code, whereas "Null" is a 
predefined type, having only value, namely "null", which by definition 
means the "primitive value that represents the intentional absence of 
any object value".

> NULL literally means an absence of a value.

"NULL" is as such an undefined identifier, whereas "null" is a special 
value of a special type. The formulation "representing the absence of an 
object value" means that "null" is intended for use in a context where 
objects are referred to and a special indicator of lack of object is needed.

A simple example is a linked list, where each item contains some data 
and a reference to the next item in the list. In the last item, the 
property for such a reference is set to the value "null" so that the end 
of the list can be determined. This value is different from not setting 
any value, or setting it to "undefined". (Although "undefined" could be 
used for indicating list end, it would not be good programming practice, 
since attempts to use "undefined" should normally be treated as errors, 
in order to make it easier to detect flaws in program logic, whereas the 
use of "null" is normal good practice.)

-- 
Yucca, http://www.cs.tut.fi/~jkorpela/

Thread

Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-28 20:19 -0700
  Re: Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-28 21:46 -0700
    Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-05-29 08:20 +0300
      Re: Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-29 07:56 -0700
        Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-05-29 19:15 +0300
          Re: Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-29 10:35 -0700
            Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-05-29 21:52 +0300
            Re: Difference between == and ===? Gregor Kofler <usenet@gregorkofler.com> - 2012-05-29 21:34 +0200
            Re: Difference between == and ===? Dr J R Stockton <reply1222@merlyn.demon.co.uk.not.invalid> - 2012-05-30 19:53 +0100
              Re: Difference between == and ===? Scott Sauyet <scott.sauyet@gmail.com> - 2012-05-31 04:52 -0700
                Re: Difference between == and ===? Dr J R Stockton <reply1222@merlyn.demon.co.uk.not.invalid> - 2012-06-01 21:41 +0100
    Re: Difference between == and ===? Gregor Kofler <usenet@gregorkofler.com> - 2012-05-29 09:34 +0200
      Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-05-29 14:13 +0200
        Re: Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-29 08:08 -0700
          Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-05-29 17:32 +0200
            Re: Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-29 08:50 -0700
          Re: Difference between == and ===? "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-05-29 16:26 +0000
            Re: Difference between == and ===? Jason Kim <iamjsonkim@gmail.com> - 2012-05-29 10:36 -0700
              Re: Difference between == and ===? Scott Sauyet <scott.sauyet@gmail.com> - 2012-05-29 10:52 -0700
              Re: Difference between == and ===? "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-05-29 21:50 +0000
                Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-05-30 07:46 +0300
                Re: Difference between == and ===? "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-05-30 07:48 +0000
                Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-05-30 11:08 +0300
                Re: Difference between == and ===? "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-05-30 14:36 +0000
                Re: Difference between == and ===? John G Harris <john@nospam.demon.co.uk> - 2012-05-30 15:26 +0100
                Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-05-30 20:17 +0300
                Re: Difference between == and ===? John G Harris <john@nospam.demon.co.uk> - 2012-06-01 14:54 +0100
                Re: Difference between == and ===? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-01 13:09 -0700
                Re: Difference between == and ===? Gene Wirchenko <genew@ocis.net> - 2012-06-01 13:49 -0700
                Re: Difference between == and ===? Daniel Pitts <newsgroup.nospam@virtualinfinity.net> - 2012-06-01 14:21 -0700
                Re: Difference between == and ===? John G Harris <john@nospam.demon.co.uk> - 2012-06-03 11:41 +0100
                Re: Difference between == and ===? Dr J R Stockton <reply1223@merlyn.demon.co.uk.not.invalid> - 2012-06-04 20:02 +0100
                Re: Difference between == and ===? BGB <cr88192@hotmail.com> - 2012-06-05 10:06 -0500
                Re: Difference between == and ===? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-06-05 18:12 +0000
                Re: Difference between == and ===? BGB <cr88192@hotmail.com> - 2012-06-05 21:23 -0500
                Re: Difference between == and ===? Norman Peelman <npeelmandog@cfl.rr.com> - 2012-06-05 23:16 -0400
                Re: Difference between == and ===? "Jukka K. Korpela" <jkorpela@cs.tut.fi> - 2012-06-06 07:55 +0300
                Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-06 08:27 +0200
                Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-06 21:22 +0200
                Re: Difference between == and ===? Dr J R Stockton <reply1223@merlyn.demon.co.uk.not.invalid> - 2012-06-06 18:56 +0100
                Re: Difference between == and ===? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-06-07 07:12 +0000
                Re: Difference between == and ===? Dr J R Stockton <reply1223@merlyn.demon.co.uk.not.invalid> - 2012-06-08 20:11 +0100
                Re: Difference between == and ===? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-06-09 14:22 +0000
                Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-06 08:28 +0200
                Re: Difference between == and ===? "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2012-06-06 09:51 +0000
                Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-06 21:22 +0200
                Re: Difference between == and ===? BGB <cr88192@hotmail.com> - 2012-06-06 08:35 -0500
                Re: Difference between == and ===? Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2012-06-06 21:19 +0200
                Re: Difference between == and ===? John G Harris <john@nospam.demon.co.uk> - 2012-05-30 15:07 +0100
  Re: Difference between == and ===? John G Harris <john@nospam.demon.co.uk> - 2012-05-30 15:44 +0100
  Re: Difference between == and ===? Stefan Weiss <krewecherl@gmail.com> - 2012-06-01 10:05 +0200
    Re: Difference between == and ===? Ross McKay <au.org.zeta.at.rosko@invalid.invalid> - 2012-06-01 20:05 +1000
    Re: Difference between == and ===? "Evertjan." <exjxw.hannivoort@interxnl.net> - 2012-06-01 15:56 +0000

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