Recoil

Recoil is a state management library for React, developed as an experimental project by the Facebook engineering team and released in 2020. The library was designed to address the challenges of managing global state in large React applications while maintaining the component-based, bottom-up philosophy that React developers expect. Recoil introduces two core primitives: atoms, which represent units of shared state that can be read and written from any component, and selectors, which are pure functions that derive new state from atoms or other selectors with built-in caching and automatic dependency tracking. Together, atoms and selectors form a directed acyclic data-flow graph where updates propagate only along affected paths, avoiding unnecessary re-renders. Selectors support both synchronous and asynchronous computation, enabling components to subscribe to data from APIs or databases through the same API used for local state, with automatic suspense integration for loading states and error boundaries for failure handling. The library provides cross-app observation through snapshots, allowing developers to implement persistence, routing, time-travel debugging, and undo functionality by observing all state changes without impairing code-splitting. Recoil integrates seamlessly with React concurrent features and Suspense, providing useRecoilState, useRecoilValue, and useSetRecoilState hooks that behave like built-in React hooks. The library does not require context providers at the root of the application, and atoms can be dynamically created at runtime. The project is open source under the MIT license with development on GitHub under the facebookexperimental organization.