Use `(?:...)` when parentheses need to group a pattern but their matched text should not become a capture. This keeps captures focused on the results you actually need; the trade-off is that complex patterns can become a little harder to read. section 10.4.4
Repeat a prefix without an extra capture
In `/((?:ninja-)+)sword/`, the inner group lets `+` repeat `ninja-` without capturing it separately. The outer group captures the full prefix. section 10.4.4
Listing 10.8. Grouping without capturing
const pattern = /((?:ninja-)+)sword/; #A
const ninjas = "ninja-ninja-sword".match(pattern);
assert(ninjas.length === 2,"Only one capture was returned.");
assert(ninjas[1] === "ninja-ninja-",
"Matched both words, without any extra capture.");
See the pattern return one capture for `ninja-ninja-`, rather than an additional capture for the repeated group. section 10.4.4
Noncapturing groups can also group alternatives: `(?:.|\s)*` matches across newlines without creating an unintended capture. The character-class alternative `/[\S\s]*/` is described as generally optimal. section 10.6.1
