Isalpha, isalnum in Javascript?

[A.P.]

Hello,
I would like to know if there's a way to check if a character is
alphanumeric or if it belongs to a certain class of characters without
having to check explictly for al the cases with an endless if. I've
tried with character>='A' and also with the Ascii code but I had no
success.
Please answer to my mailbox too. Thank you very much in advance.

[Thomas Salvador]

hi.

>having to check explictly for al the cases with an endless if. I've
>tried with character>='A' and also with the Ascii code but I had no
>success.

hmmm, this should work.

function isalpha(c) {
return (((c >= 'a') && (c <= 'z')) || ((c >= 'A') && (c <= 'Z')));
}

function isdigit(c) {
return ((c >= '0') && (c <= '9'));
}

function isalnum(c) {
return (isalpha(c) || isdigit(c));
}

bye

--
thomas....@fernuni-hagen.de -+- http://www.come.to/salvador aka
http://www.stud.fernuni-hagen.de/q4307909/welcome.htm

[Thogek]

thomas....@fernuni-hagen.de writes:
>>having to check explictly for al the cases with an endless if. I've
>>tried with character>='A' and also with the Ascii code but I had no
>>success.
>
>hmmm, this should work.
>
> function isalpha(c) {
> return (((c >= 'a') && (c <= 'z')) || ((c >= 'A') && (c <= 'Z')));
> }
>
> function isdigit(c) {
> return ((c >= '0') && (c <= '9'));
> }
>
> function isalnum(c) {
> return (isalpha(c) || isdigit(c));
> }

Here's some funky-looking functions that'll also work:

var alphas = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ";
var digits = "0123456789";

function isAlpha(c) {
return (alphas.indexOf(c) != -1);
}

function isDigit(c) {
return (digits.indexOf(c) != -1);
}

function isAlphaNum(c) {
return (isAlpha(c) || isDigit(c));
}

--
========================================================================
Thogek
tho...@alumni.caltech.edu
http://www.alumni.caltech.edu/~thogek

[ms.20...@gmail.com]

On Friday, 2 January 1998 10:00:00 UTC+2, A.P. wrote:
> Hello,
> I would like to know if there's a way to check if a character is
> alphanumeric or if it belongs to a certain class of characters without

> having to check explicitly for all the cases with an endless if. I've

> tried with character>='A' and also with the Ascii code but I had no
> success.

> Please answer to my mailbox too. Thank you very much in advance.

You can use regex expressions to check, but it will check for English letters,
code:
var isAlpha = (c) => (/[A-Za-z]/).test(c);

[JJ]

I taut I taw a millennial.

[dr.j.r....@gmail.com]

On Friday, 17 January 2020 16:05:20 UTC, JJ wrote:

> On Fri, 17 Jan 2020 00:50:09 -0800 (PST), ms.2052001#gmail.com wrote:
> > On Friday, 2 January 1998 10:00:00 UTC+2, A.P. wrote:
> >> Hello,

> > ...

> > var isAlpha = (c) => (/[A-Za-z]/).test(c);
>
> I taut I taw a millennial.

Indeed. The answers given might have been reasonable in those far-off days, but appear inadequate now, except for those who believe that the only real characters are those on the keyboard of an American PC.

ISTM that Java has a Character entity, with methods such as Character.getType(), and that Java can access many sorts of information about characters which we here could write as \u0000 to \uFFFF - and higher.

So : what information can modern JavaScript obtain about Unicode characters such as the single characters `xi` and `XI` and strange characters existing in Eastern alphabets such as Danish, Russian, Japanese ... ?


--
(c) John Stockton, near London, UK. Using Google Groups. |
Mail: J.R.""""""""@physics.org - or as Reply-To, if any. |

[Ben Bacarisse]

If you have ECMAScript 9, you can use

/\p{Letter}/u

as the pattern to match all Unicode characters with property
General_Category = Letter. Still not 100%, but it might be what's wanted.

--
Ben.

[dr.j.r....@gmail.com]

On Friday, 17 January 2020 21:10:12 UTC, Ben Bacarisse wrote:

> If you have ECMAScript 9, you can use

Well, yes, but for Web authors the need must be for the readers to have ECMAscript 9.

> /\p{Letter}/u
>
> as the pattern to match all Unicode characters with property
> General_Category = Letter. Still not 100%, but it might be what's wanted.

My up-to-date Firefox 72.0.1 (64-bit) then appears not to have ECMAScript 9. Is there now a way in ECMAScript to determine the ECMAScript version number?

H'mm - if there is such a way, it would be necessary, I suppose, to use the above RegExp within try...catch, and compose a moderately graceful failure.

[JJ]

On Sat, 18 Jan 2020 02:42:22 -0800 (PST), dr.j.r....@gmail.com wrote:
>
> My up-to-date Firefox 72.0.1 (64-bit) then appears not to have ECMAScript
> 9. Is there now a way in ECMAScript to determine the ECMAScript version
> number?

Probably not.

> H'mm - if there is such a way, it would be necessary, I suppose, to use
> the above RegExp within try...catch, and compose a moderately graceful
> failure.

It can be determined by checking feature presence and/or functionalities.

[JJ]

On Fri, 17 Jan 2020 13:07:27 -0800 (PST), dr.j.r....@gmail.com wrote:
>
> So : what information can modern JavaScript obtain about Unicode
> characters such as the single characters `xi` and `XI` and strange
> characters existing in Eastern alphabets such as Danish, Russian,
> Japanese ... ?

Only the code point.

[Thomas 'PointedEars' Lahn]

Much more after reading in the Unicode Character Database (BTDT in my JSX,
see UnicodeData.js, UnicodeData.txt, and jsx.regexp.RegExp in regexp.js):

<http://www.unicode.org/ucd/>

<https://stackoverflow.com/a/8568325/855543> (my answer in 2011)

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

[Michael Haufe (TNO)]

On Saturday, January 18, 2020 at 4:42:29 AM UTC-6, dr.j.r...@gmail.com wrote:
> On Friday, 17 January 2020 21:10:12 UTC, Ben Bacarisse wrote:
>
> > If you have ECMAScript 9, you can use
>
> Well, yes, but for Web authors the need must be for the readers to have ECMAscript 9.

There is a babel plugin for this:

<https://babeljs.io/docs/en/next/babel-plugin-proposal-unicode-property-regex.html>

with an example:

<https://mothereff.in/regexpu#input=var+regex+%3D+/%5Cp%7BScript_Extensions%3DGreek%7D/u%3B&unicodePropertyEscape=1>

[Julio Di Egidio]

On Friday, 17 January 2020 22:10:12 UTC+1, Ben Bacarisse wrote:
> ms.20...@gmail.com writes:
> > On Friday, 2 January 1998 10:00:00 UTC+2, A.P. wrote:
> >> Hello,
> >> I would like to know if there's a way to check if a character is
> >> alphanumeric or if it belongs to a certain class of characters without
> >> having to check explicitly for all the cases with an endless if. I've
> >> tried with character>='A' and also with the Ascii code but I had no
> >> success.
> >> Please answer to my mailbox too. Thank you very much in advance.
> >
> > You can use regex expressions to check, but it will check for English letters,
> > code:
> > var isAlpha = (c) => (/[A-Za-z]/).test(c);

You would use Unicode code points in character ranges, as in the last
example here:
<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Guide/Regular_Expressions/Character_Classes>

> If you have ECMAScript 9, you can use
>
> /\p{Letter}/u

If all you have is a hammer...

> as the pattern to match all Unicode characters with property
> General_Category = Letter. Still not 100%, but it might be what's
> wanted.

LOL. Haven't you and the others noticed that you are replying to a thread
from 1998? As far as I remember, at the time JS didn't have RegExp at all,
and even a quite limited support (certainly browser-wise) for Unicode in
strings: which is the reason for that question...

Julio

[dr.j.r....@gmail.com]

On Sunday, 19 January 2020 18:07:34 UTC, Julio Di Egidio wrote:


> LOL. Haven't you and the others noticed that you are replying to a thread
> from 1998?

One does not reply to a thread; one replies to an article. My first article in the thread was only technically a Reply; in essence, it proposed renewing the question.

> As far as I remember, at the time JS didn't have RegExp at all,
> and even a quite limited support (certainly browser-wise) for Unicode in
> strings: which is the reason for that question...

That may depend on which parts of 1998 you remember.

I am holding David Flanagan's JavaScript Pocket Reference, First Edition, October 1998. Its Object Reference part includes a RegExp section (Availability, Core JavaScript 1.2), and its description of the String Data Type says that ECMA-262 requires support of full 16-bit Unicode.

It does say that IE4 supports Unicode but Navigator 4 does not.

His Definitive Guide, 3rd Edn, says much the same, at greater length; the Preface is dated April 1998, publication June 1998.

[Julio Di Egidio]

On Monday, 20 January 2020 00:39:53 UTC+1, dr.j.r...@gmail.com wrote:
> On Sunday, 19 January 2020 18:07:34 UTC, Julio Di Egidio wrote:
>
> > LOL. Haven't you and the others noticed that you are replying to a thread
> > from 1998?
>
> One does not reply to a thread; one replies to an article. My first article
> in the thread was only technically a Reply; in essence, it proposed renewing
> the question.

Besides that it's not an article but just a technical question, I hadn't
even mentioned it but it is actually VERY inappropriate to resurrect years
old threads, you guys still can't get your head around the fact that this
is not a forum and you are rather messing up with the Usenet ARCHIVE.

I mean, I am even being charitable, you guys have no fucking clue...

HTH and EOD.

Julio