Using two capturing groups with JavaScript's replace() function

Question

Given such a string +as[23+"AS@D"-@] replace all instances of @ between the [ and ] with the number right after the [ (in this case: 23). Please answer using JavaScript (a suggestion is using .replace()). So using this algorithm, +as[23+"AS@D"-@] will be changed to +as[23+"AS23D"-23]

Here is my regex \[(\d+)[^\]]*(\@*)\] The second capturing group is not captured (Regexr tells me that nothing is captured within the second capturing group). I need help on making the second capturing group capture all instances of @

I have tried using Mozilla Developer for help, but it did not work. Any help will be appreciated. Answers have to have explanation.

If this question is not clear enough, please tell me in the comments how can this be improved.

I'm voting to close this question as off-topic because stackoverflow is not a code writing service. — melpomene, Nov 08 '15 at 16:04
Why do you think the second capturing group "is not captured"? (And what do you mean by that?) — melpomene, Nov 08 '15 at 16:07
@melpomene I think there is an error with my regex. If the regex works, then I would have solved my problem. — user41805, Nov 08 '15 at 16:08
@melpomene http://www.regexr.com/ tells me that nothing is captured in the second capturing group. — user41805, Nov 08 '15 at 16:10
The second capturing group captures a string of length zero (`[\@]*` (better written as `@*`) matches 0 or more `@` signs). It matches 0 times because there are no `@` signs following the number `[23`. — melpomene, Nov 08 '15 at 16:11
@melpomene My newest code doesn't work either: `\[(\d+)[^\]]*(\@*)\]` — user41805, Nov 08 '15 at 16:13
In that version, `+"AS@D"-@` is matched by `[^\]]*`; `\@*` (better written as `@*`) has nothing left, so matches 0 characters. Then `\]` matches the final `]`. — melpomene, Nov 08 '15 at 16:16
Er. That's for you to figure out, isn't it? I mean, it's your homework. — melpomene, Nov 08 '15 at 16:20
You should split it to 2 operations: 1. get a number, 2. replace all '@' to a number. — vp_arth, Nov 08 '15 at 16:28

score 0 · Accepted Answer · answered Nov 08 '15 at 16:22

You can use replace with a callback function in Javascript:

var s = '+as[23+"AS@D"-@]';
var r = s.replace(/\[(\d+)[^\]]*\]/, function($0, $1) {
                   return $0.replace(/@/g, $1);});
//=> +as[23+"AS23D"-23]

$0 represents whole string between [ and ] and $1 is the first capture group i.e. number right after [.

Using two capturing groups with JavaScript's replace() function

1 Answers1