Capturing Group Regex Javascript match returns two values why?

Question

Why does "abcabcabc".match(/(abc){3}/);

return two entries ["abcabcabc", "abc"] ? both "abcabcabc" and "abc"

similarly,

["1234", "1234"]

Answer 1

Every regexp has an implicit capturing group around it, which is stored in result 0.

The second result comes from your capturing group (abc) . Most regexp implementations only keep the last match of that capturing group.

Answer 2

/(abc){3}/ :

• 1st Capturing Group (abc){3}

  {3} Quantifier — Matches exactly 3 times

  A repeated capturing group will only capture the last iteration. Put a capturing group around the repeated group to capture all iterations or use a non-capturing group instead if you're not interested in the data.

  abc matches the characters abc literally (case sensitive)

So the first value is the whole match, ie "abcabcabc" .

The second value is the last iteration captured by (abc) , ie "abc" .