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From: Cezary Tomczyk <cezary.tomczyk@gmail.com>
Newsgroups: comp.lang.javascript
Subject: Re: regexp 0 - 3 digits
Date: Wed, 15 Mar 2017 09:29:58 +0100
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On 15/03/2017 09:19, Evertjan. wrote:
> Cezary Tomczyk <cezary.tomczyk@gmail.com> wrote on 15 Mar 2017 in
> comp.lang.javascript:
>
>> On 15/03/2017 04:55, JJ wrote:
>>> On Wed, 15 Mar 2017 14:39:22 +1100, Andrew Poulos wrote:
>>>> I have this string
>>>>    dd:dd:dd,ddd
>>>> where the d's are digits and I'm using this to match it
>>>>    match(/^[0-9][0-9]:[0-9][0-9]:[0-9][0-9],[0-9][0-9][0-9]/);
>>>>
>>>> Now I find that after the comma there may be from 0 to 3 digits.
>>>>
>>>> How can I modify the expression to handle that?
>>>>
>>>> Andrew Poulos
>>>
>>>   /^[0-9][0-9]:[0-9][0-9]:[0-9][0-9],[0-9]{0,3}/
>>>
>>> You can short it to:
>>>
>>>   /^[0-9]{2}:[0-9]{2}:[0-9]{2},[0-9]{0,3}/
>>
>> or to:
>>
>> /^[\d]{2}:[\d]{2}:[\d]{2},[\d]{0,3}/
>
> \d\d is shorter than \d{2}

Yes and it does the same.

> No reason for the '[]'s
> and
> '\d\d' is shorter than '\d{2}'
>
> /^\d\d:\d\d:\d\d,\d{0,3}/
>
> Meseems you want no trailing characters,
> so add a final '$':
>
> /^\d\d:\d\d:\d\d,\d{0,3}$/
>
> But probably you want to have no comma,
> when there are zero decimals:
>
> /^\d\d:\d\d:\d\d(,\d{1,3})?$/
>
> or if you want to make the comma optional,
> when no decimals:
>
> /^\d\d:\d\d:\d\d(,|,\d{1,3})?$/
>
> ==================
>
> testing:
>
> <script type='text/javascript'> 'use strict'
> 	function w(x,a) { document.write(x.test(a)+'<br>'); };
> 	w(/^\d\d:\d\d:\d\d(,\d{1,3})?$/, '01:01:01,12'); // true
> 	w(/^\d\d:\d\d:\d\d(,\d{1,3})?$/, '01:01:01,12 '); // false
> 	w(/^\d\d:\d\d:\d\d(,\d{1,3})?$/, '01:01:01'); // true
> 	w(/^\d\d:\d\d:\d\d(,\d{1,3})?$/, '01:01:01,'); // false
> 	w(/^\d\d:\d\d:\d\d(,|,\d{1,3})?$/, '01:01:01'); // true
> 	w(/^\d\d:\d\d:\d\d(,|,\d{1,3})?$/, '01:01:01,'); // true
> </script>

Nice.

Btw this is a very good case as a candidate to write first unit tests 
and then required function.

-- 
Cezary Tomczyk
http://www.ctomczyk.pl/
https://www.aslint.org/ - Accessibility linting tool