Valtio is a proxy-based state management library and reactive state engine that provides a mutable state store. It allows application state to be updated through direct object mutations rather than immutable patterns, using JavaScript proxies to track changes and trigger updates. For React applications, it includes a synchronization hook that ensures components re-render only when the specific properties they access are modified.
The system supports reactive data derivation through computed properties that automatically update when their underlying dependencies change. It maintains reactivity across deep data structures via nested proxy composition and extends this tracking to native Map and Set collections.
Additional capabilities include state composition for nesting or splitting state objects and the ability to subscribe to changes across the entire state tree. The library provides mechanisms for transient state updates to read values without triggering re-renders and supports the storage of untracked objects to reduce memory overhead.