Add PUT /users/:id update endpoint

Adds updateUser to db/store.js and a PUT /:id route to routes/users.js.
Validates required fields (400), handles missing users (404), and returns
the updated user on success (200).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>

Author: QuanTranDoanAnh

NOTES.md

@@ -0,0 +1,10 @@
+# Model:
+I use Sonnet model
+
+# Changes: Add PUT /users/:id endpoint
+
+Added an update-user endpoint to the users resource following the existing patterns in the codebase.
+
+**`db/store.js`** — added `updateUser(id, { name, email })`: locates the user by id using `findIndex`, returns `undefined` if not found, otherwise replaces the record in-place and returns the updated user. Exported alongside the existing store methods.
+
+**`routes/users.js`** — added `PUT /users/:id` handler: converts the `:id` param to a number, rejects requests missing `name` or `email` with a 400 error, calls `store.updateUser` and returns 404 if the user doesn't exist, otherwise responds with the updated user object and a 200 status.

db/store.js

@@ -24,4 +24,11 @@ function createUser({ name, email }) {
   return user;
 }
 
-module.exports = { getAllUsers, getUserById, createUser };
+function updateUser(id, { name, email }) {
+  const index = users.findIndex((u) => u.id === id);
+  if (index === -1) return undefined;
+  users[index] = { ...users[index], name, email };
+  return users[index];
+}
+
+module.exports = { getAllUsers, getUserById, createUser, updateUser };

routes/users.js

@@ -20,6 +20,23 @@ router.get("/:id", (req, res) => {
   res.json(user);
 });
 
+// PUT /users/:id — update an existing user, or 404 if it doesn't exist
+router.put("/:id", (req, res) => {
+  const id = Number(req.params.id);
+  const { name, email } = req.body;
+
+  if (!name || !email) {
+    return res.status(400).json({ error: "name and email are required" });
+  }
+
+  const user = store.updateUser(id, { name, email });
+  if (!user) {
+    return res.status(404).json({ error: "User not found" });
+  }
+
+  res.json(user);
+});
+
 // POST /users — create a user; name and email are required
 router.post("/", (req, res) => {
   const { name, email } = req.body;