i did

No, you just have to make sure that the User class works appropriately. The test will create User instances and assert that your internal logic is right.

my code is correct

Yeah, you can say that once it's accepted, not before.

what the return should looks like ?

What do you mean? You need to write a class with specified methods, and return types are different for each. Unfortunately for JS there don't seem to be any sample tests. You can try switching to some other language (if you understand it) to see what the tests look like, or just hit 'Attempt'.

If your tests are all green, but you are getting timeout, then it usually means that your solution returns correct answers, there are no failed assertions, but test suite did not manage to run to its end before time run out. Your code is not failing, but it's too slow.

Can you also please delete duplicated message below?

if you know append(), you'll be okay. i think its about logic and ordering