Path: csiph.com!v102.xanadu-bbs.net!xanadu-bbs.net!feeder.erje.net!eu.feeder.erje.net!newsfeed.datemas.de!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: Puzzling JS Error
Date: Fri, 10 Apr 2015 00:20:52 +0200
Organization: PointedEars Software (PES)
Lines: 38
Message-ID: <4117321.jCF6XAfRs9@PointedEars.de>
References: <consduF625qU1@mid.individual.net>
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 1428618179 3972 eJwNxskBwDAIA7CVEsAEj5PD7D9Cq5fgOfOuSGSg0f/ECNPx0hxeY6ntMXlCb9AK3nsn2wjpfgwiEO8= (9 Apr 2015 22:22:59 GMT)
X-Complaints-To: abuse@news.solani.org
NNTP-Posting-Date: Thu, 9 Apr 2015 22:22:59 +0000 (UTC)
User-Agent: KNode/4.14.2
X-User-ID: eJwNysERACEIBLCWgFsWKEdQ+y/hnHzjH5UToBN+H845IUjFreotsUZiOknf1oo09JRNi+nO4gq1iHmFWNd/SjcVOQ==
Cancel-Lock: sha1:nlDyuAhmaL9H6I/4BK0kPlf2qdI=
X-NNTP-Posting-Host: eJwFwQkBwDAIA0BLZeGVQ2HxL6F3BhefUDdXo1EalahBBqf6cjfP/ti4qJhPnafVJuZQWPIAJZARcA==
Xref: csiph.com comp.lang.javascript:27284

Mel Smith wrote:

> ****** fragment of Ajax set up code ********
> 
> var HTTP;
> /*
> // problem in this next statement
> if (HTTP && (typeof HTTP !== "object" || HTTP.NAME)) {
>     throw new Error("Namespace 'HTTP' already exists");
>    }
> */
> alert("Ready toComplete Ajax set up.") ;

Please post *real* code.

With *this* code, the alert will be displayed because you have *commented 
out* the offending code.

If we assume that you have not commented it out, there will never be thrown 
an exception because, barring an assignment to “HTTP” earlier, the value of 
the “HTTP” variable is the “undefined” value, the sole value of the 
Undefined type, with which all variables are initialized if they are not 
initialized explicitly.

“undefined“ is type-converted to boolean “false”, and shortcut evaluation of 
a logical AND expression causes the remaining operands to be ignored if one 
operand evaluates to “false” (because the result can never become “true” by 
further evaluation).

Next time, before you post use the debugger that is nowadays built into 
*all* Web browsers (by virtue of the most of them being based on WebKit, 
Gecko or MSHTML); see the FAQ.

-- 
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.