XState

Use XState when the domain has meaningful modes, transitions, async lifecycle, cancellation, guards, delays, or actor boundaries. The goal is not "state management"; the goal is to make the process explicit, typed, inspectable, and hard to misuse.

Core Standard

• Prefer setup({ types, actors, actions, guards, delays }).createMachine(...) for typed machines with named implementations.
• Put finite modes in states.
• Put durable facts in context.
• Put side effects behind actors, actions, guards, and delays.
• Put request data in invoke.input.
• Put UI decisions on snapshots: matches, hasTag, can, and selected context.
• Initialize each actor instance with input.
• Define default implementations in setup(...); replace runtime implementations with .provide(...).
• Model later external changes as keyed remounts, domain events, or subscription actors.

Reading Guide

Read only the references needed for the task:

• Modeling: states, state types, context, events, guards, tags, delays.
• Transitions: guarded, eventless, delayed, and pure transitions.
• Actors: async work, actor choice, invocation, outputs, cancellation.
• Promises: fromPromise, request input, output, errors, abort signals.
• Callbacks: subscriptions, imperative APIs, sendBack, receive, cleanup.
• Observables: observable snapshots and observable event streams.
• Child Actors: invoke, spawn, spawnChild, child ownership, inspection.
• React: @xstate/react, .provide(...), actor input, selectors.
• Testing: actor tests, waitFor, provided implementations, timing.

Working Loop

1. Name the process and its legal modes.
2. Define the domain events.
3. Decide what data survives transitions.
4. Move effects into actors or named implementations.
5. Connect UI through actor hooks and snapshot reads.
6. Test behavior at the actor boundary.