Q1. What properties are commonly used on the request object?
Important req properties: req.params (route parameters), req.query (query string), req.body (parsed body), req.headers (HTTP headers), req.method (HTTP method), req.url (URL), req.cookies (cookies with cookie-parser), and req.ip (client IP).
Q2. What methods are commonly used on the response object?
Common res methods: res.send(), res.json(), res.status(), res.redirect(), res.render() (for templates), res.set() (set headers), res.cookie() (set cookies), res.end() (end response), and res.download() (send file for download).
Q3. How do you set HTTP status codes in Express?
Use res.status(code). It's chainable: res.status(201).json({...}). Common codes: 200 OK, 201 Created, 400 Bad Request, 401 Unauthorized, 403 Forbidden, 404 Not Found, 500 Internal Server Error.
Q4. How do you access request headers?
Through req.headers object. Example: const authHeader = req.headers['authorization']. Header names are lowercase. You can also use req.get(headerName). For cookies, you need cookie-parser middleware, then req.cookies.
Q5. What's the difference between res.send() and res.end()?
res.send() automatically sets appropriate Content-Type and ends the response. It can send objects, strings, buffers. res.end() simply ends the response without sending data. Use res.send() for most cases; res.end() is for when you just want to end without data.