In JavaScript regular expressions, parentheses have different meanings, capturing parentheses ( ... ) and non-capturing parentheses (?: ... ) are used differently.
Capture brackets ( ... ):
Capturing parentheses ( ... ) in a regular expression capture what is matched within the parentheses into a group and generate a corresponding capturing group when matched. This means you can use the contents of the capture group after the regex match. For example:
const regex = /(foo){1,2}/;
const input = 'foofoo';
const match = input.match(regex);console.log(match[1]); // Output "foo"
In the above example, the regular expression matches consecutive occurrences of "foo" and captures one of them into a capture group.
Non-capturing parentheses (?: ... ):
Non-capturing parentheses (?: ... ) are also a form of parentheses, but they do not create capturing groups. This means that the contents of the parentheses will still be used for matching, but will not be captured in any specific group. This is useful in situations where you want to match a set of subexpressions but don't need to keep the results of each subexpression. For example:
const regex = /(?:foo){1,2}/;
const input = 'foofoo';
const match = input.match(regex);console.log(match[0]); // Output "foofoo"
In this example, non-capturing parentheses are used, so no capturing group is generated, but the regular expression will still match consecutive occurrences of "foo".
In summary, the main difference between capturing parentheses and non-capturing parentheses is whether to create a capturing group, and whether to preserve the matching result of the subexpression when matching. If you only need to match without retaining the result of the subexpression, then using non-capturing parentheses (?: ... ) would be more appropriate.