How do you prevent Cross-Site Scripting (XSS)?

Short answer: Sanitize user inputs and outputs. Use libraries like DOMPurify for front-end. Use HTTP headers like Content Security Policy (CSP) via Helmet. Escape data before rendering in HTML.

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.