捕获组：`(...)`

Parentheses (...) have two functions in one:

1. Group sub-patterns, so that a quantifier applies to the whole group ((ab)+ matches ab, abab, ababab).
2. Capture the matched substring, exposing it as a numbered group accessible separately (group 1, 2, 3… from left to right based on the opening parenthesis).

Pattern: (\d{4})-(\d{2})-(\d{2})
Sample:  Data: 2024-03-15.
               ^^^^^^^^^^
Gruppi:
  match  = "2024-03-15"
  gruppo1 = "2024"
  gruppo2 = "03"
  gruppo3 = "15"

The editor on the right shows the groups under each match.

Quantifying a group

Without parentheses, ab+ means "a followed by one or more b". With parentheses it becomes "one or more ab":

Pattern   Matcha su 'ababab':
ab+       'ab' (poi 'a' e 'b' separati, non collegati)
(ab)+     'ababab' come gruppo unico

Capture group indices and usage

Each pair of parentheses not preceded by special characters creates a numbered capture group. Group 1 corresponds to the first open parenthesis, group 2 to the second, and so forth. In JavaScript, you can access these groups via the array returned by exec or matchAll.

Try it

Review exercise

Additional challenge