What is the purpose of the main field in package.json?

Short answer: It specifies the entry point file of a package (default is index.js). When someone imports your package, Node.js loads the file in main.

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.