What is React?
Answer
React is an open-source JavaScript library for building user interfaces, developed and maintained by Meta (formerly Facebook) and a large community of contributors. First released in 2013, React introduced a component-based architecture where UIs are broken into small, reusable pieces called components. React's core innovation is the Virtual DOM — an in-memory representation of the real DOM that React uses to compute the minimal set of changes needed, then batch-updates the actual DOM efficiently. React follows a declarative programming model: you describe what the UI should look like based on state, and React takes care of updating the DOM to match. React is unopinionated about routing, state management, and data fetching — it is a view library, not a full framework. It is used to build single-page applications (SPAs), mobile apps via React Native, and server-rendered apps via Next.js.