$ show statelyai/xstate
XState is a production-grade TypeScript library for creating, interpreting, and executing finite state machines and statecharts, based on the SCXML standard and the actor model. The repository is a monorepo (pnpm workspaces) containing the core `xstate` package, the lighter `@xstate/store` for event-sourced state management, and framework-specific bindings for React, Vue, Svelte, Solid, Preact, and Angular. It also includes `xstate-inspect` for debugging, `xstate-immer` for Immer integration, a graph analysis module for model-based testing, and many example applications and templates. The core engine provides `createMachine`, `createActor`, `setup()` for type-safe machine definitions, built-in actions (assign, sendTo, raise, etc.), guard combinators, and actor logic factories (`fromPromise`, `fromCallback`, `fromObservable`). The store sub-package offers atoms, source atoms, and composable extensions like persist and undo/redo. The codebase demonstrates high craftsmanship with extensive TypeScript type inference, well-encapsulated modules, and comprehensive test coverage. It is actively maintained with continuous CI/CD and version management via changesets.
The LLM identified 4 files worth highlighting for reuse:
The `setup()` function is the primary entry point for declaring a state machine with full type safety. It provides a builder pattern that accepts typed configurations for actions, guards, delays, actors, and schemas, then returns an object with `createMachine()` and other factory methods. This pattern enables compile-time validation of machine logic and is a reusable, composable approach to building complex statecharts.
`fromPromise` is a factory that converts a promise-returning function into actor logic conforming to the XState actor model. It manages lifecycle states (idle, pending, resolved, rejected) and integrates with the actor system (system, self, input). This is a reusable pattern for wrapping any async operation (e.g., API calls, timers) as a first-class actor, enabling declarative orchestration.
The `persist` extension implements state persistence for `@xstate/store` with two strategies: snapshot (periodically saves full context) and event (logs events with checkpoint replay). It supports custom storage adapters (including BroadcastChannel for cross-tab sync), throttling, data migration, and filtering. The extension is composed via `.with(persist(...))` and is a clean, reusable solution for adding durable state to any store.
`getShortestPaths` computes all shortest transition paths from a given state machine state to all reachable states using a breadth-first search. It is part of the graph analysis toolkit used with `TestModel` to generate minimal test sequences for model-based testing. The algorithm is well-encapsulated and reusable for any graph-based state exploration beyond XState.