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Asked: 2026-06-01T20:22:55+00:00

What’s the difference between this regex: /(everything|cool)/gi and this one: /(?:everything|cool)/gi ? I’m asking

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What’s the difference between this regex: /(everything|cool)/gi and this one: /(?:everything|cool)/gi ?

I’m asking this because I’ve got an regex which I wasn’t able to write myself* and there are, as you can see below, a lot of ?: in that regex. I’ve read somewhere that ?: is bad for performance so I want to remove it.Can I remove it or is it important for anything?

* (?:(?=(?:(?:\\.|"(?:\\.|[^"\\])*"|[^\\'"])*'(?:\\.|"(?:\\.|[^"'\\])*"|[^\\'])*')*(?:\\.|"(?:\\.|[^"\\])*"|[^\\'])*$)(?=(?:(?:\\.|'(?:\\.|[^'\\])*'|[^\\'"])*"(?:\\.|'(?:\\.|[^'"\\])*'|[^\\"])*")*(?:\\.|'(?:\\.|[^'\\])*'|[^\\"])*$)(?:\\.|[^\\'"]))+

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1 Answer

  1. Editorial Team

    Without ?:, a reference to a matched group is created.
    With a ?:, the group is matched, but not captured.

    Here’s a benchmark on both methods: http://jsperf.com/regex-capture-vs-non-capture

    By looking at the bars, one would say that the non-captured groups are faster. However, if you look at the bottom, the differences can be neglected, since both methods are already incredibly fast.

    Removing or adding ?: to an existing solution might break the code, so I advise to not edit the RegExp when it’s not causing any issues.

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