Javascript - Greedy regex issue

Question

My regex must match what's within /* @DT-HIDE / and / @/DT-HIDE */. It's fine until a page contains two blocks.

If there are two blocks, well, $1 will match all that's between the first opening @DT-HIDE and last @/DT-HIDE. I suppose it's about a greedy * instead of an ? but I can't figure it out.

Regex:

const pattern = new RegExp(/(\/\*\s@DT-HIDE\s\*\/) ([\s\S]*?) (\/\*\s@\/DT-HIDE\s\*\/)/g);

Example value being processed:

/* @DT-HIDE */
function(){
    return "...";
}
/* @/DT-HIDE */

/* @DT-HIDE */
function logic(url){
    return new Promise( (resolve, reject) => {
        ...
    });
}
/* @/DT-HIDE */

Since you're using the new RegExp() constructor, it's a shame you don't pass it a string rather than a /.../ construct : you would avoid having to escape slashes inside the regexp. You would instead need to escape double-quotes, which wouldn't be a problem in your case. — Aaron
– Aaron, Commented May 30, 2017 at 15:34
Hah.. As I can see the only problem are the two spaces you have between the groups (between the brackets): /(\/\*\s@DT-HIDE\s\*\/)([\s\S]*?)(\/\*\s@\/DT-HIDE\s\*\/)/g. Also you don't need the constructor simply assign the regex to the pattern variable — Slim
– Slim, Commented May 30, 2017 at 15:36
@CasimiretHippolyte right, although they already need to be escaped in /.../ constructs — Aaron
– Aaron, Commented May 30, 2017 at 21:23

Wiktor Stribiżew · Accepted Answer · 2017-05-30 17:19:41Z

You should have had [\s\S]* in your original pattern, otherwise you would not obtain a "greedy" match.

However, as Slim noticed, the spaces you introduced failed the match since there is no space after /* @DT-HIDE */. So, you may solve the issue by removing the spaces. Declaring the pattern with a conbstructor notation is a good idea when your pattern contains many slashes, but in this case you may use a regex literal without the RegExp constructor:

const pattern = /(\/\*\s@DT-HIDE\s\*\/)([\s\S]*?)(\/\*\s@\/DT-HIDE\s\*\/)/g;

However, the pattern is not optimal, since the lazy dot matching patterns may involve many "forward-trackin" steps. I suggest unrolling it as

const pattern = /(\/\*\s@DT-HIDE\s\*\/)([^\/]*(?:\/(?!\*\s@\/DT-HIDE\s\*\/)[^\/]*)*)(\/\*\s@\/DT-HIDE\s\*\/)/g;
                                        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

See the regex demo.

The [^\/]*(?:\/(?!\*\s@\/DT-HIDE\s\*\/)[^\/]*)* will make matching more efficient especially if the number of / is not that big in between the delimiters.

Collectives™ on Stack Overflow

Javascript - Greedy regex issue

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related