Glossary

Action: An effect scheduled by a transition, entry, or exit function through the enqueue argument (enq).

Actor: A running process that receives events and produces snapshots.

Actor logic: The rules used by an actor to process events. Created with createMachine(...), createAsyncLogic(...), and the other logic creators.

Actor reference (ActorRef): The object used to interact with an actor: send events, subscribe, and read snapshots.

Choice state: A state with type: 'choice' that immediately routes to another state based on a choice function.

Context: Data stored in a state machine snapshot.

Delayed transition: A transition configured with after that runs once its state has been active for a duration.

Durable step: A step inside async logic (enq.step(key, fn)) whose result is recorded on the snapshot so it is not re-executed after restoring the actor.

Emitted event: An event published by an actor through enq.emit(...) and observed with actor.on(...). Emitted events do not change the actor's state.

Event: A value sent to an actor. Events have a type.

Eventless transition: A transition configured with always that runs without an external event.

Final state: A state with type: 'final' that completes its parent. A top-level final state completes the machine actor.

Guard: A condition that chooses whether a transition can run.

History state: A state with type: 'history' that records and restores the previously active child state of its parent.

Input: Data provided when an actor is created, or to a state via a transition's input.

Internal event: An event listed in internalEvents that can be raised inside the machine but rejected when sent from outside the actor.

Invoked actor: A child actor whose lifecycle belongs to a state.

Output: Final data produced when an actor completes.

Parallel state: A state with type: 'parallel' whose child regions are all active at the same time.

Registry key: A name that registers an actor in its system so other actors can look it up with system.get(...).

Route state: A state with an id and a route that can be navigated to directly with an xstate.route event.

Selector: A memoized, subscribable view of an actor's snapshot created with actor.select(...).

Snapshot: An actor's observable state at one point in time. Snapshot status is active, done, error, or stopped.

Spawned actor: A child actor created during a transition with enq.spawn(...) and managed by its parent.

State: A named mode in a state machine.

State machine: A model with a finite set of states and transitions.

Statechart: A state machine with features such as nested, parallel, and history states.

System: The tree of actors created by a root actor, including its registry of named actors.

Timeout: A limit configured with timeout/onTimeout on a state or invocation, or with timeout on async logic.

Transition: A response to an event that may change state, context, or run effects.

Wildcard: An event pattern such as pointer.* or * that matches a family of event types when no exact transition matches.