API

const machine = createMachine(definition, options)

Options

Option	Meaning
scripts	name → function, for string references in the definition.
context	merged over definition.context, shallowly.
state	a stored value to restore instead of entering and settling.
onSend	(event) before an event is processed.
onTransition	(state) after start, send and back.
onChange	({...context}, event) after a transition that carried actions.
onFinal	(state) when the root reaches final.

The merge is shallow, and the machine mutates its context. If definition.context holds nested objects, build it with a factory instead — otherwise every machine compiled from that definition shares them.

Methods

Method	Returns
start(event?)	enters the initial state, settles, resolves to the state.
send(type, payload?)	processes an event, settles, resolves to the state.
back(event?)	moves to the previous step on the trail. Deliberately does not settle.
path()	the trail as dotted ids, e.g. ["profile.name", "billing.card"].
route(segments)	{ target, prev }.
state()	{ value, context, done }. Synchronous.

Everything except state() is async. start() is idempotent. send() before start() throws.

back() does not settle on purpose: settling from the previous step would walk straight forward again, because the answer that opened the guard is still there.

State value

A snapshot is { value, context, done }. value follows the xstate convention: "idle", { parent: "child" }, { region: { a: "x", b: "y" } }.

state() called before start() reports undefined for value.

Helpers

assign(updates)

Builds an action from an object of values or (context, event) functions.

assign({ email: (_ctx, event) => event.value })

toPath(value) / toValue(segments)

toPath({ profile: 'name' })   // ["profile", "name"]
toValue(['profile', 'name'])  // { profile: "name" }

Series-only. See URLs.

Errors

The engine throws rather than degrading, at compile time where it can:

• target "x" not found from "y" — a transition points at nothing reachable.
• state "x" has child states but no initial — a compound state without an entry.
• parallel state "x" has no regions
• script "x" is not a function — a name with no options.scripts entry.
• call start() before send()
• microstep limit reached: machine has a transition loop — 1000 microsteps without settling.

@1state/validate reports the first group of these, plus schema and reachability problems, without running the flow.