Add a Product in TypeScript

Until now every route used GET, the method for reading. To send new data, a client uses POST. Express picks the function by the path and the method together, so GET /products and POST /products can go to two different functions.

A POST carries a request body, usually a JSON object. Express reads a JSON body only when you ask it to, with app.use(express.json()); near the top of the file; then req.body holds the body as a JavaScript object, with the TypeScript type any. When something new is stored, the answer has the status 201 Created, written like the 404: res.status with the number, then .json with the body. Here is the idea on another route:

app.use(express.json());

const messages: string[] = [];

app.post("/messages", (req: Request, res: Response) => {
  const data = req.body;
  messages.push(data.text);
  res.status(201).json({ count: messages.length });
});

The client doesn't choose the id: the shop gives the new product the largest id so far, plus 1, and stores it in products, so every route sees it. Your code must give, in this order:

POST /products  {"name": "Plant", "price": 15, "category": "home"}  →  201  {"id": 5, "name": "Plant", "price": 15, "category": "home"}
POST /products  {"name": "Stapler", "price": 9, "category": "office"}  →  201  {"id": 6, "name": "Stapler", "price": 9, "category": "office"}
GET /products/6  →  200  {"id": 6, "name": "Stapler", …}
GET /products?category=office  →  200  [{"id": 2, …}, {"id": 4, …}, {"id": 6, …}]
GET /products/count  →  200  {"count": 6}

Your task: add a POST /products route that reads the JSON body from req.body, gives the new product the next id, pushes it to products as a Product and answers it with the status 201. Turn on express.json() so Express reads the body.

Assignment
Follow the Coding Tutorial to build the POST /products route, from app.post to the 201 answer.

Hint
Find the largest id with a variable of type number that starts at 0, declared with let, and a loop that keeps the biggest id it has seen. Build the new product in newProduct with the type Product, not in product, and answer it with res.status(201) followed by .json.