What does a server action do in the Next.js app router?

It is a function that handles an action like a form submission on the server. Here, the server action saves a guestbook entry into the in-memory server store.

How do I verify the new entry shows up on the list?

Run npm test for the server action, then use npm run dev and on /guestbook submit an entry and confirm it appears on the list, newest-first, right after submitting.

Where is the data stored?

In the in-memory server store in lib/guestbook-store.ts. That store is already complete and needs no changes; a DB and login are out of scope.

Guestbook

Your task

Build a guestbook. Submitting an entry saves it, and right after submitting, the new entry shows up on the /guestbook list. Complete the addEntry server action and the list view.

Ground rules

•Data lives in an in-memory server store (guestbook-store). No DB, no login.

Not required

•Editing/deleting entries, pagination, advanced input validation.

▶About this challenge

Build a guestbook with the Next.js app router. A server action saves an entry, and the /guestbook list shows entries newest-first. Data lives in an in-memory server store — no DB, no login. Complete it so the new entry appears on the list right after submitting.

In the Next.js app router, the list page is rendered on the server, and saving an entry is handled by a server action. This problem is about when and how a change to the data carries through to the list the user sees. The habit that matters is confirming not just that the entry was saved, but that it actually appears on the list right after submitting — both on screen and in tests.

What does a server action do in the Next.js app router?: It is a function that handles an action like a form submission on the server. Here, the server action saves a guestbook entry into the in-memory server store.
How do I verify the new entry shows up on the list?: Run npm test for the server action, then use npm run dev and on /guestbook submit an entry and confirm it appears on the list, newest-first, right after submitting.
Where is the data stored?: In the in-memory server store in lib/guestbook-store.ts. That store is already complete and needs no changes; a DB and login are out of scope.