What is middleware in Express.js?

Short answer: Middleware is a function that runs between the request and response cycle. It can: Modify request/response Execute logic Call the next middleware 📌

Example code

app.use((req, res, next) => { console.log(`${req.method} ${req.url}`); next(); // Move to next middleware or route });

Real-world example (ShopNest)

Express middleware authenticates JWT, then the /orders route handler creates the order.

Say this in the interview

1. Define — one clear sentence (the short answer above).
2. Example — relate it to a project like ShopNest or your real work.
3. Trade-off — when you would not use it.