Question

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Non capturing group?

I’m learning regex in JavaScript, and the (?:x) character or “non-capturing parentheses” just doesn’t make sense to me. If you don’t want the match to be remembered why not just abandon parentheses altogether? What’s the advantage of using /(?:x)/ instead of just /x/?

Answer 1

Because you might need the parentheses for other reasons. For example, suppose you want to capture the digit at the end of abababababab9. If you wrote ab*(\d) then it would match abbbbbbbbb9. You need to parenthesize the ab so that the * operator will repeat the whole thing. (ab)*(\d). But maybe you don’t care about how many times ab was repeated. That’s where you use (?:): (?:ab)*(\d).