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Message-ID: <1805042.BzeuYpbCYS@PointedEars.de>
From: Thomas 'PointedEars' Lahn <PointedEars@web.de>
Reply-To: Thomas 'PointedEars' Lahn <cljs@PointedEars.de>
Organization: PointedEars Software (PES)
Date: Fri, 02 Nov 2012 18:41:48 +0100
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Subject: Re: Good use of bitwise NOT "~" or unnecessary obfuscation?
Newsgroups: comp.lang.javascript
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Patricia Shanahan wrote:

> On 11/2/2012 2:22 AM, Evertjan. wrote:
> ...
>> if ( /foo/.test(someString) ) {..}
>>
>> I trust not understanding Regex is not a valid counterargument.
> 
> If I'm prepared to look at it long enough, I can generally work out what
> a Regex does, but Regex does not seem to me to be a very human-friendly,
> smoothly readable language.

That depends on the flavor and your experience with them.
 
> For this particular case, it looks OK if the probe really is a literal
> such as "foo".

In exactly that case using a Regular Expression is overkill.  You need to 
consider that for every RegExp literal in the code (and per ES 5.x in every 
use of that literal), a new RegExp instance is being created.

> Could you show me the code you would use for this if the probe were an
> actual parameter or variable with unknown contents?
> 
> That is, what would you use to replace:
> 
> if(someString.indexOf(someOtherString)) != -1)

It is possible with

  if ((new RegExp(someOtherString)).test(someString))

but I would not use that.  However, the following can be useful and 
necessary:

  if ((new RegExp(someOtherString, "i")).test(someString))

The caveat in both cases is that any special characters in the value of 
`someOtherString' that should not assume their special meaning need to be 
escaped.  This can be accomplished with a previous replace() –

  if ((new RegExp(someOtherString.replace(/…/g), "i")).test(someString))

– or with a user-defined method:

  if ((new RegExp(jsx.regexp.escape(someOtherString), "i"))
      .test(someString))

One could also augment the ECMAScript String prototype object:

  if ((new RegExp(someOtherString.regexpEscape(), "i"))
      .test(someString))
  
See jsx.dom.css.addClassName() for a working example of a variable RegExp:

<http://PointedEars.de/websvn/filedetails.php?repname=JSX&path=%2Ftrunk%2Fdom%2Fcss.js>


PointedEars
-- 
Danny Goodman's books are out of date and teach practices that are
positively harmful for cross-browser scripting.
  -- Richard Cornford, cljs, <cife6q$253$1$8300dec7@news.demon.co.uk> (2004)