regular expressions difference between ((?:[^\"])) and ([^\"])

Question

what is the difference between this regular expressions are the replaceable?

((?:[^\"])*)


([^\"]*)

background to this question:

The javascript WYSIWYG editor (tinymce) fails to parse my html code in Firefox (23.0.1 and 25.0a2) but works in in Chrome.

I found the regular expression to blame:

attrRegExp = /([\w:\-]+)(?:\s*=\s*(?:(?:\"((?:[^\"])*)\")|(?:\'((?:[^\'])*)\')|([^>\s]+)))?/g;

which I modified, replacing

((?:[^\"])*)

with

([^\"]*)

and

((?:[^\'])*)

with

([^\']*)

the resulting regular expression is working in both browsers for my test case

attrRegExp = /([\w:\-]+)(?:\s*=\s*(?:(?:\"([^\"]*)\")|(?:\'([^\']*)\')|([^>\s]+)))?/g

can someone put some light on that?

my test data that only works with the modified regular expression is a big image >700 kb like:

var testdata = '<img alt="" src="data:image/jpeg;base64,/9j/4AAQSkZJRgA...5PmDk4FOGOHy6S3JW120W1uCJ5M0PBa54edOFAc8ePX/2Q==">'

doing something like that to test:

testdata.match(attrRegExp);

especially when the test data is big the unmodified regex is likely to fail in firefox.

You can find the jsfiddle example here:

@Cybȫʁgϟ37: That won't help OP at all, since he is not to blame for the code of TinyMCE (I suppose) — Niklas B., Sep 13 '13 at 14:46
By the way, you don't need to escape quotes in a regex. Do you see any difference when using `"` instead of `\"` (and `'` instead of `\'`)? — Tim Pietzcker, Sep 15 '13 at 09:02
Possible duplicate: http://stackoverflow.com/questions/6418985/capturing-group-in-regex — Sumurai8, Sep 15 '13 at 11:05
The only difference is that the former doesn't capture groups, the latter does. That is, you can use \num back references in the latter. — g13n, Sep 15 '13 at 16:36
@Sumurai8, g13n: No, both regexes do capture around the repetition. Only at the first one the repeated character class is enclosed in a non-capturing group, while it is not in the second — Bergi, Sep 15 '13 at 21:16

nmaier · Accepted Answer · 2013-09-15T17:51:05.260

There should be no difference in the result. So you should be fine.

However, there might be a big difference in how RegExp engines will process these two expressions, and in the case of Firefox/Safari you just proved there actually is ;)

Firefox makes use of WebKit/JavaScriptCore YARR. YARR imposes an arbitrary, artificial limit, which hits in the non-capturing group variant

// The below limit restricts the number of "recursive" match calls in order to
// avoid spending exponential time on complex regular expressions.
static const unsigned matchLimit = 1000000;

As such Safari is affected as well.

See the relevant Webkit bug and relevant Firefox bug and the nice test case comparing different expression types somebody put together.

regular expressions difference between ((?:[^\"])*) and ([^\"]*)

1 Answers1

regular expressions difference between ((?:[^\"])) and ([^\"])