mobx-state-tree

mobx-state-tree (often called MST) is a state management library for JavaScript and TypeScript applications. State management refers to how an app keeps track of its data as users interact with it: which items are in a shopping cart, whether a user is logged in, what posts are loaded in a feed. MST is built on top of another library called MobX and adds structure and organization on top of it.

The library is aimed at teams that want reactive updates with less code than alternatives like Redux. Reactive means that when data changes, anything that depends on that data updates automatically. MST makes this work while keeping a clear model of the application's shape, so developers can see what data exists and how it is organized. TypeScript users get type-checking for free, catching errors before the code runs.

The core concept is a model: a definition of what a piece of data looks like. Models can reference each other, hold computed values derived from other data, and define actions that are the only allowed way to change the data. This structure makes it easy to trace where changes come from, which helps when debugging. Snapshots, an idea influenced by Redux, let the app capture the entire state at a point in time and restore it later, which is useful for undo features or debugging.

MST pairs especially well with React and React Native. When the app state changes, only the React components that actually depend on the changed data re-render, which can be a meaningful performance improvement in large applications. The library has zero external dependencies beyond MobX itself.

There is a free egghead.io course and official documentation site for learning MST. The project is maintained with support from Infinite Red, a React Native consulting company.