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textarea multi-line regex

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  textarea multi-line regex Denis McMahon <denismfmcmahon@gmail.com> - 2013-08-17 12:56 +0000
    Re: textarea multi-line regex Martin Honnen <mahotrash@yahoo.de> - 2013-08-17 15:10 +0200
      Re: textarea multi-line regex "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-08-17 17:13 +0200
      Re: textarea multi-line regex Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-08-18 10:57 +0200
        Re: textarea multi-line regex "Joao Rodrigues (J.R.)" <groups_jr-1@yahoo.com.br> - 2013-08-19 11:04 -0300
    Re: textarea multi-line regex Denis McMahon <denismfmcmahon@gmail.com> - 2013-08-17 13:18 +0000
      Re: textarea multi-line regex Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-08-18 10:29 +0200
      Re: textarea multi-line regex Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-08-18 19:24 +0100
        Re: textarea multi-line regex "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-08-18 23:11 +0200
          Re: textarea multi-line regex Denis McMahon <denismfmcmahon@gmail.com> - 2013-08-18 21:36 +0000
            Re: textarea multi-line regex "Evertjan." <exxjxw.hannivoort@inter.nl.net> - 2013-08-19 00:50 +0200
            Re: textarea multi-line regex Dr J R Stockton <reply1300@merlyn.demon.co.uk.invalid> - 2013-08-19 19:48 +0100
        Re: textarea multi-line regex Stefan Weiss <krewecherl@gmail.com> - 2013-08-19 00:18 +0200
    Re: textarea multi-line regex Thomas 'PointedEars' Lahn <PointedEars@web.de> - 2013-08-18 10:22 +0200

#20966 — textarea multi-line regex

I'm trying to trim whitespace from the text in a textarea:

I assume that there are at least two non whitespace characters in the 
textarea.

function trim( id ) {

var re = /^\s*(\S.*\S)\s*$/m;

var cap = re.exec( document.getElementById( id ).value );

if ( cap.length == 2 ) document.getElementById( id ).value = cap[1];

}

Now I think that:

the first "\s*" should capture all whitespace before the first non-
whitespace character;

the second "\s*" should capture all whitespace after the last non-
whitespace character;

the "(\S.*\S)" should capture ereything except the leading and trailing 
whitespace (from the first non whitespace character to the last non 
whitespace character inclusive);

"/m" should mean that the whole capture works across multiple lines.

However, the textarea is set to the trimmed first line of the original 
only.

Any ideas why multiline matching isn't working the way I expect? I 
suspect that the ".*" in the middle of "(\S.*\S)" isn't being greedy 
across line breaks.

Example page:

http://www.sined.co.uk/tmp/textareatrim.htm

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#20967

Denis McMahon wrote:
> I'm trying to trim whitespace from the text in a textarea:
>
> I assume that there are at least two non whitespace characters in the
> textarea.
>
> function trim( id ) {
>
> var re = /^\s*(\S.*\S)\s*$/m;
>
> var cap = re.exec( document.getElementById( id ).value );
>
> if ( cap.length == 2 ) document.getElementById( id ).value = cap[1];
>
> }
>
> Now I think that:
>
> the first "\s*" should capture all whitespace before the first non-
> whitespace character;
>
> the second "\s*" should capture all whitespace after the last non-
> whitespace character;
>
> the "(\S.*\S)" should capture ereything except the leading and trailing
> whitespace (from the first non whitespace character to the last non
> whitespace character inclusive);
>
> "/m" should mean that the whole capture works across multiple lines.
>
> However, the textarea is set to the trimmed first line of the original
> only.
>
> Any ideas why multiline matching isn't working the way I expect? I
> suspect that the ".*" in the middle of "(\S.*\S)" isn't being greedy
> across line breaks.


I think the "." dot does not match the "\n" character.

If you want to trim leading and trailing white space can't you simply use
    string = string.replace(/^\s+|\s+$/g, '')
? See also http://jibbering.com/faq/#trimString.

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#20973

Martin Honnen wrote on 17 aug 2013 in comp.lang.javascript:

> I think the "." dot does not match the "\n" character.

[\s\S] does.

-- 
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

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#20978

Martin Honnen wrote:

> I think the "." dot does not match the "\n" character.

Correct.

> If you want to trim leading and trailing white space can't you simply use
>     string = string.replace(/^\s+|\s+$/g, '')

  string = string.replace(/^\s+/, '').replace(/\s+$/, '');

might be more efficient:

<http://blog.stevenlevithan.com/archives/faster-trim-javascript>

ECMAScript Edition 5 introduces String.prototype.trim():

  string = string.trim();

<http://PointedEars.de/es-matrix/?filter=trim>
<http://ecma-international.org/ecma-262/5.1/#sec-15.5.4.20>
<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/String/Trim>

The following pattern appears to be useful:

  string = (typeof string.trim == "function"
    ? string.trim()
    : string.replace(/^\s+/, '').replace(/\s+$/, ''));

You may want to emulate the “trim” method if you cannot be sure it is 
implemented, and you need to trim more than one time:

  if (typeof String.prototype.trim != "function")
  {
    String.prototype.trim = function () {
      return this.replace(/^\s+/, '').replace(/\s+$/, '');
    };
  }

  // …

  string = string.trim();

(Emulations backwards compatible to the earliest versions of ECMAScript 
implementations, and beyond, are also conceivable.)

> ? See also http://jibbering.com/faq/#trimString.

An update there is indicated.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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#20993

Em 18/08/2013 05:57, Thomas 'PointedEars' Lahn escreveu:
> Martin Honnen wrote:
>> If you want to trim leading and trailing white space can't you simply use
>>      string = string.replace(/^\s+|\s+$/g, '')
>
>    string = string.replace(/^\s+/, '').replace(/\s+$/, '');
>
> might be more efficient:
>
> <http://blog.stevenlevithan.com/archives/faster-trim-javascript>
>
<snip>
>
> You may want to emulate the “trim” method if you cannot be sure it is
> implemented, and you need to trim more than one time:
>
>    if (typeof String.prototype.trim != "function")
>    {
>      String.prototype.trim = function () {
>        return this.replace(/^\s+/, '').replace(/\s+$/, '');
>      };
>    }
>
>    // …
>
>    string = string.trim();
>
> (Emulations backwards compatible to the earliest versions of ECMAScript
> implementations, and beyond, are also conceivable.)
>
>> ? See also http://jibbering.com/faq/#trimString.
>
> An update there is indicated.

Thomas, would please update the version in your site?
<http://pointedears.de/scripts/faq/cljs/#trimString>

--
Joao Rodrigues (J.R.)

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#20968

On Sat, 17 Aug 2013 12:56:27 +0000, Denis McMahon wrote:

> var re = /^\s*(\S.*\S)\s*$/m;

Meh, solved it now - in multiline . doesn't match newlines but \s does so:

var re = /^\s*(\S[\S\s]*\S)\s*$/m;

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#20977

Denis McMahon wrote:

> On Sat, 17 Aug 2013 12:56:27 +0000, Denis McMahon wrote:
>> var re = /^\s*(\S.*\S)\s*$/m;
> 
> Meh, solved it now - in multiline . doesn't match newlines

“.” *never* matches newline (e.g., never "\n" or "\r").  This is why 
jsx.regexp.RegExp introduces PCRE's “s” modifier:

<http://PointedEars.de/scripts/test/regexp>

> but \s does so:

“\s” matches whitespace which *includes* the newline characters "\n" and 
"\r".
 
> var re = /^\s*(\S[\S\s]*\S)\s*$/m;

This is pointless for matching newline.  There cannot be newline in a line 
except at the end (where it is _not_ considered in multiline mode).

If you want to match across several lines, you do _not_ want multiline mode.  
Curious, but true.

-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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#20987

In comp.lang.javascript message <kunt7j$bdr$2@dont-email.me>, Sat, 17
Aug 2013 13:18:43, Denis McMahon <denismfmcmahon@gmail.com> posted:

>On Sat, 17 Aug 2013 12:56:27 +0000, Denis McMahon wrote:
>
>> var re = /^\s*(\S.*\S)\s*$/m;
>
>Meh, solved it now - in multiline . doesn't match newlines but \s does so:
>
>var re = /^\s*(\S[\S\s]*\S)\s*$/m;

I have a recollection, which needs checking, that in a RegExp [^]
matches more than . does; but that is not _necessarily_ in a JavaScript
RegExp, or even anywhere true.
 ... ... ...
<http://www.merlyn.demon.co.uk/js-valid.htm#RG> refers

-- 
 (c) John Stockton, nr London UK               Reply address via Home Page.
   news:comp.lang.javascript FAQ <http://www.jibbering.com/faq/index.html>.
   <http://www.merlyn.demon.co.uk/js-index.htm> jscr maths, dates, sources.
   <http://www.merlyn.demon.co.uk/> TP/BP/Delphi/jscr/&c, FAQ items, links.

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#20988

Dr J R Stockton wrote on 18 aug 2013 in comp.lang.javascript:

> I have a recollection, which needs checking, that in a RegExp [^]
> matches more than . does; but that is not _necessarily_ in a JavaScript
> RegExp, or even anywhere true.

Conceptually, [^] should match any string but an empty one.

And in practice it seems to do the job:

alert(/[^]/.test(',')); // true
alert(/[^]/.test('\n')); // true
alert(/[^]/.test('')); // false

Even more interesting is [], 
not matching any string, not even an empty one: 

alert(/[]/.test(',')); // false
alert(/[]/.test('\n')); // false
alert(/[]/.test('')); // false

What would match only empty strings?
I mean as a regex, this one not being quite cricket:

alert(!/[^]/.test('')); // true


-- 
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

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#20989

On Sun, 18 Aug 2013 23:11:49 +0200, Evertjan. wrote:

> What would match only empty strings?
> I mean as a regex, this one not being quite cricket:

How about: /^$/

-- 
Denis McMahon, denismfmcmahon@gmail.com

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#20991

Denis McMahon wrote on 18 aug 2013 in comp.lang.javascript:

> On Sun, 18 Aug 2013 23:11:49 +0200, Evertjan. wrote:
> 
>> What would match only empty strings?
>> I mean as a regex, this one not being quite cricket:
> 
> How about: /^$/

Elementary, my dear D.

-- 
Evertjan.
The Netherlands.
(Please change the x'es to dots in my emailaddress)

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#20998

In comp.lang.javascript message <kureou$npc$1@dont-email.me>, Sun, 18
Aug 2013 21:36:30, Denis McMahon <denismfmcmahon@gmail.com> posted:

>On Sun, 18 Aug 2013 23:11:49 +0200, Evertjan. wrote:
>
>> What would match only empty strings?
>> I mean as a regex, this one not being quite cricket:
>
>How about: /^$/

<http://www.merlyn.demon.co.uk/quotings.htm#Donatus>;
and /ibid/ #FrancisDrake on debugging.

-- 
 (c) John Stockton, nr London, UK.   E-mail, see Home Page.    Turnpike v6.05.
 Website  <http://www.merlyn.demon.co.uk/> - w. FAQish topics, links, acronyms
 PAS EXE etc. : <http://www.merlyn.demon.co.uk/programs/> - see in 00index.htm
 Dates - miscdate.htm estrdate.htm js-dates.htm pas-time.htm critdate.htm etc.

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#20990

On 2013-08-18 20:24, Dr J R Stockton wrote:
> In comp.lang.javascript message <kunt7j$bdr$2@dont-email.me>, Sat, 17
> Aug 2013 13:18:43, Denis McMahon <denismfmcmahon@gmail.com> posted:
>>Meh, solved it now - in multiline . doesn't match newlines but \s does so:
>>
>>var re = /^\s*(\S[\S\s]*\S)\s*$/m;
> 
> I have a recollection, which needs checking, that in a RegExp [^]
> matches more than . does; but that is not _necessarily_ in a JavaScript
> RegExp, or even anywhere true.

That is the case in JavaScript (and ECMAScript). Unfortunately, it's a
syntax error in IE8. IE9 and IE10 handle it correctly. The same goes for [].

- stefan

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#20976

Denis McMahon wrote:

> "/m" should mean that the whole capture works across multiple lines.

No, it means that the meaning of “^” changes from “start of input” to “start 
of line”, and of “$” from “end of input” to “end of line”.
 
-- 
PointedEars

Twitter: @PointedEars2
Please do not Cc: me. / Bitte keine Kopien per E-Mail.

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