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createMachine()

createMachine<S, E>(definition, initial): object

createMachine<S, E, C>(definition, initial, initialContext): object

Creates a finite state machine.

Type Parameters​

S: S extends string​

Union of state names

E: E extends string​

Union of event names

C: C​

Context type

Parameters​

Overload 1:

definition: MachineDefinition<S, E, undefined>​

The state/transition map

initial: S​

The initial state

Overload 2:

definition: MachineDefinition<S, E, C>​

The state/transition map

initial: S​

The initial state

initialContext: C​

The initial context value

Returns: object​

A machine with current, send, matches, trySend, onTransition, reset

current(): () => S​

Returns: S​

send(): (event) => S​

event: E
Returns: S

matches(): (state) => boolean​

state: S
Returns: boolean

trySend(): (event) => Option<S>​

event: E
Returns: Option<S>

onTransition(): (listener) => () => void​

listener: TransitionListener<S, E>
Returns: > (): void

Returns: void​

reset(): () => void​

Returns: void​

Since​

2.4.0

Example​

const door = createMachine({
  locked: { unlock: { to: "closed" } },
  closed: { open: { to: "opened" }, lock: { to: "locked" } },
  opened: { close: { to: "closed" } },
}, "locked");

door.send("unlock"); // "closed"
door.send("open");   // "opened"
door.matches("opened"); // true

SimpleTransition<S>​

Interface

A simple transition to a target state.

Since​

2.4.0

Type Parameters​

S: S extends string​

Union of state names

Properties​

to​

readonly to: S

ContextTransition<S, C>​

Interface

A transition that updates context.

Since​

2.4.0

Type Parameters​

S: S extends string​

Union of state names

C: C​

Context type

Properties​

to: S​

update(): (ctx) => C​

ctx: C
Returns: C

Transition<S, C>​

Type

Transition<S, C> = SimpleTransition<S> | ContextTransition<S, C>

A transition is either simple (just target) or with context update.

Type Parameters​

S: S extends string​

Union of state names

C: C​

Context type

Since​

2.4.0

Transitions<S, E, C>​

Type

Transitions<S, E, C> = { readonly [K in E]?: Transition<S, C> }

A transition map for a single state.

Type Parameters​

S: S extends string​

Union of state names

E: E extends string​

Union of event names

C: C​

Context type

Since​

2.4.0

MachineDefinition<S, E, C>​

Type

MachineDefinition<S, E, C> = { readonly [K in S]: Transitions<S, E, C> }

Full state machine definition.

Type Parameters​

S: S extends string​

Union of state names

E: E extends string​

Union of event names

C: C​

Context type

Since​

2.4.0

TransitionListener()<S, E>​

Type

TransitionListener<S, E> = (from, event, to) => void

A transition listener receives the previous state, the event, and the new state.

Type Parameters​

S: S extends string​

Union of state names

E: E extends string​

Union of event names

Parameters​

from: S​

event: E​

to: S​

Returns: void​

Since​

2.4.0