How do you validate request data in a REST API?

Short answer: You can use validation libraries to ensure incoming data is valid. 📌 Example with express-validator: npm install express-validator const { body, validationResult } = require('express-validator'); app.post('/users', body('email').isEmail(), (req, res) => { const errors = validationResult(req);

Example code

if (!errors.isEmpty()) return res.status(400).json({ errors: errors.array() }); res.send('User created'); });

Real-world example (ShopNest)

A ShopNest BFF in Node.js aggregates catalog and price APIs for the React storefront.

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.