MobX

MobX is a state management library for JavaScript and TypeScript applications, created by Michel Weststrate and built on the principles of transparent functional reactive programming. The library uses a signal-driven architecture where observable state, derived computations, and reactions automatically track dependencies at runtime, ensuring that only the minimal set of computations are re-evaluated when state changes. Unlike libraries that require immutable updates and explicit action dispatchers, MobX allows direct mutation of observable objects, arrays, and maps through plain JavaScript assignment, with changes propagated synchronously to all observers. The core primitives include observable for creating reactive state, computed for derived values that are cached and only recalculated when their dependencies change, autorun and reaction for side effects triggered by state changes, and when for explicit transactional batching of multiple mutations. The observer HOC from mobx-react-lite integrates MobX with React components, causing them to re-render only when the specific observable values they actually read during render change, without manual selector functions or memoization. MobX supports fine-grained observability where individual object properties become independent reactive nodes, enabling granular dependency tracking. The library has over 50,000 GitHub stars and platinum sponsors including Canva, Coinbase, Facebook, Mendix, and Guilded. MobX is framework-agnostic and works with React, Vue, Angular, and vanilla JavaScript. The project is open source under the MIT license with extensive documentation in English, Chinese, and Korean.