Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!1.eu.feeder.erje.net!ecngs!feeder2.ecngs.de!46.4.82.166.MISMATCH!weretis.net!feeder1.news.weretis.net!news.solani.org!.POSTED!not-for-mail
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Newsgroups: comp.lang.javascript
Subject: Re: Why does (a,b,c) return only c?
Supersedes: <2074322.mqz4NpIYxF@PointedEars.de>
Date: Tue, 26 May 2015 12:26:19 +0200
Organization: PointedEars Software (PES)
Lines: 46
Message-ID: <1687513.QYX3roR0lP@PointedEars.de>
References: <55630af5$0$13000$c3e8da3$5496439d@news.astraweb.com> <gf4c3c-iks.ln1@mail.binaryfoundry.ca> <XnsA4A5DF4D39BAAeejj99@194.109.133.246> <mk07ei$t55$1@speranza.aioe.org>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Mime-Version: 1.0
Content-Type: text/plain; charset="UTF-8"
Content-Transfer-Encoding: 8Bit
X-Trace: solani.org 1432636140 20493 eJwFwYkRwDAMArCV/EEu47jk2H+ESmgmdYbgwPD6bWVuxQrcowBh3QigPlvyNJ0Yvu71Dyi6EXg= (26 May 2015 10:29:00 GMT)
X-Complaints-To: abuse@news.solani.org
NNTP-Posting-Date: Tue, 26 May 2015 10:29:00 +0000 (UTC)
User-Agent: KNode/4.14.2
Cancel-Key: sha1:s6GXb/bxrfWOfpRFittlgVbpOk4=
X-User-ID: eJwFwYEBwCAIA7CXBEvRc0DW/09YEpvGl2AQoVAK94Qt4xUK85Ex1YbK8dez+0PsdDIfF1tXXC7S3OZ0/UYdFTg=
Cancel-Lock: sha1:MtPHDCsivGzpUDk5d0QvI/Mah4k=
X-NNTP-Posting-Host: eJwFwQEBwDAIAzBLbGvh2IGCfwlP+Px4B5wOLtf37rzwSeRMW9dNOxRUSMxrKbQso7bsqx8scxH7
Xref: csiph.com comp.lang.javascript:27880

Joao Rodrigues wrote:

> But why on Earth would someone use comma operators? Because they let you
> specify more than one expression where JavaScript expects only one. See
> examples at:
> <https://javascriptweblog.wordpress.com/2011/04/04/the-javascript-comma-operator/>

Bogus.

| //original
| var a = 7, 5;
| //apply = operator
| var a, 5; //a is now 7
| //SyntaxError: missing variable name 

is not a syntax error because “we [haven’t] wrapped the variable assignment 
in parentheses”, but because _“5” is not a valid variable name_.

And the value of “a” is not 7, but _not defined_ at this line (that is 
different from the “undefined” value), because

  var a = 7, 5;

is a syntax error already:

| >>> var a = 7, 5;
| Uncaught SyntaxError: Unexpected number
|   at Object.InjectedScript._evaluateOn (<anonymous>:895:140)
|   at Object.InjectedScript._evaluateAndWrap (<anonymous>:828:34)
|   at Object.InjectedScript.evaluate (<anonymous>:694:21)

The subsequent example in that article, where it works, is

| //original
| var a = (7, 5);
| //apply group
| var a = 5;

where not only the parentheses have been inserted, but magically the comma 
has been replaced by a “=”.  Surprise.

-- 
PointedEars
FAQ: <http://PointedEars.de/faq> | SVN: <http://PointedEars.de/wsvn/>
Twitter: @PointedEars2 | ES Matrix: <http://PointedEars.de/es-matrix>
Please do not cc me. / Bitte keine Kopien per E-Mail.