Why is Node.js single-threaded?

Short answer: Node.js uses a single-threaded event loop to handle concurrency.

Explain a bit more

This design: Simplifies programming by avoiding thread-related bugs like race conditions. Uses non-blocking I/O so a single thread can handle many connections efficiently. Offloads heavy tasks (file I/O, network requests) to background threads in the libuv thread pool. So, Node.js can handle many tasks concurrently without spawning multiple OS threads for each.

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.