JavaScript regex with back reference

Question

I would like to construct regex (in JavaScript) that would return:

• for string "test" groups (test) and () second group being empty
• and for string "test-a" groups (test) and (test-a)

Is that possible?

Answer 1

Could be done with:

/(?=(test))(test-a)?/

Replace test and a with the pattern you are really looking for.

You may also want to anchor it, eg:

/^(?=(test))(?=(test-a)?)test(?:-a)?$/