Express.js questions

Middleware functions in Express are functions that have access to the request, response, and the next middleware function in the application’s request-response cycle. Implement middleware by defining a function with `(req, res, next)` parameters and using `app.use(middlewareFunction)` to apply it globally or `router.use(middlewareFunction)` for specific routes. Middleware can perform tasks such as logging, authentication, or request modification.

Implement rate limiting in Express using middleware like `express-rate-limit`. Install it with `npm install express-rate-limit` and configure it to limit the number of requests from a single IP address. For example, `const limiter = rateLimit({ windowMs: 15 * 60 * 1000, max: 100 }); app.use(limiter);` limits requests to 100 per 15 minutes. This helps prevent abuse and ensure fair usage of resources.

Error handling in Express is typically done using middleware. Define an error-handling middleware function with four parameters: `err`, `req`, `res`, and `next`. Use `app.use((err, req, res, next) => { /* error handling logic */ })` to catch and handle errors. Ensure you place this middleware after all route and other middleware definitions. Handle different error types and send appropriate responses to the client.

Express.js is a fast, minimal web framework for Node.js that simplifies server creation and request handling. Example: Express allows you to define routes and middleware in a structured way. A simple Express app might handle GET requests at '/home' with app.get('/home').

Synchronous errors are caught using try-catch blocks, while asynchronous errors should be handled with `.catch()` or async error-handling middleware. For example: `app.use(async (req, res, next) => { try { await asyncFunction(); } catch (err) { next(err); } });`.