Routing

Routing refers to how an application’s endpoints (URIs) respond to client requests. In Express, you define routes that specify what should happen when a request with a particular HTTP method (like GET, POST, etc.) and URL path is received. A route definition takes the following structure: `app.METHOD(PATH, HANDLER)`. Here, `app` is an instance of Express, `METHOD` is an HTTP request method in lowercase (e.g., `app.get`), `PATH` is a path on the server (e.g., `/about`), and `HANDLER` is the function executed when the route is matched. This handler function receives the request (`req`) and response (`res`) objects as arguments. The `req` object contains information about the incoming HTTP request, such as the URL parameters, query strings, and request body. The `res` object is used to send the HTTP response back to the client. You can send various types of responses, such as plain text (`res.send()`), JSON data (`res.json()`), or render a template (`res.render()`). Express also allows for dynamic routes using route parameters. For example, a route like `/users/:userId` will match requests for `/users/1`, `/users/abc`, etc. The value of `userId` can then be accessed in the handler via `req.params.userId`. To keep your code organized, you can use the `express.Router` class to create modular, mountable route handlers for different parts of your application.