How does Next.js differ from React, and why use it?

React is a library for building UI. Next.js is a framework built on React that adds routing, server rendering, page generation and endpoint handling, among other things.

In an interview: “I describe the UI with React, and Next.js provides the structure of the whole app and the way that UI gets delivered to the user.”

Example: a shop needs indexable product pages, while the cart needs interactivity in the browser. One app can combine both approaches.

Pitfall: Next.js doesn't replace React, and it doesn't automatically mean every page is rendered on every request.