A condition or mode a system can be in. In UI, examples include loading, idle, error, editing.

Something that happens, usually triggered by the user or system. Events ask the machine to transition.

A change from one state to another in response to an event.

A condition that must be true for a transition to occur. Also known as a conditional transition.

A side effect that occurs as part of a transition, such as sending a request or updating context.

An entity that can receive and send events, and can spawn child actors. In XState v5, every interpreted machine is an actor.

Creating a new actor from within an existing actor.

Calling a service (promise, callback, observable, or another machine) from within a state.

A state that contains multiple orthogonal regions that are active simultaneously.

A pseudo-state that remembers the previous active sub-state when re-entering a compound state.

Extended state data associated with a machine, separate from the finite state value.

A finite state machine — defined by states, events, transitions, and initial state.

An extended state machine formalism that adds hierarchy, parallelism, and history.