Measure First in TypeScript

Before you make the shop faster, measure it: otherwise you can't tell whether a change really helped. In this module you measure the work a request does by counting its database queries. A count gives the same answer on every computer, while a time in milliseconds changes with the machine and with whatever else it is doing.

Every route in the shop asks the database through one helper, runQuery: it takes the SQL as a string and returns a prepared StatementSync. So that is the one place to count: a wrapper that does its job and keeps score on the way. The score lives in an object, because the shop can send an object as JSON just as it is, and TypeScript works out its type by itself. Here is the same idea on another value, a counter of visits:

const visits = { count: 0 };

app.get("/hello", (req: Request, res: Response) => {
  visits.count += 1;
  res.json({ message: "Hi!", visits: visits.count });
});

To read the count, add a debug route: a tool for you, the developer, not a page for customers. The count only goes up, so read it before and after a request: the difference is what that request cost. Your code must give these answers, in this order:

GET /debug/queries  →  200  {"queries": 0}
GET /products/1  →  200  {"category": "kitchen", "id": 1, "name": "Mug", "price": 12, "stock": 10}
GET /debug/queries  →  200  {"queries": 1}
GET /customers/1/orders  →  200  [{"id": 1, "items": […], …}, {"id": 3, "items": […], …}]
GET /debug/queries  →  200  {"queries": 4}
GET /customers/5/orders  →  200  []
GET /debug/queries  →  200  {"queries": 5}

Customer 1's orders cost 3 queries: one for the orders, then one for the items of each of the 2 orders. Customer 5 has no orders, so only the first query runs. Reading the count is not a query, so it never counts itself.

Your task: add an object stats whose property queries starts at 0 (its type, { queries: number }, needs no annotation), make runQuery add 1 to it every time it runs, and add a route for GET /debug/queries, with req: Request and res: Response, that answers stats as JSON.

Assignment
Follow the Coding Tutorial to count every query in runQuery and show the count at GET /debug/queries.

Hint
The counting line goes first in runQuery, the helper every route uses; its signature doesn't change. += 1 adds one to the value already in the object.