***

title: "StateMachineConfig"
generated: true
---------------

## StateMachineConfig

<GenerationInfo sourceFile="packages/core/src/common/finite-state-machine/types.ts" sourceLine="89" packageName="@vendure/core" />

The config object used to instantiate a new [FSM](/current/core/reference/typescript-api/state-machine/fsm#fsm) instance.

```ts title="Signature"
interface StateMachineConfig<T extends string, Data = undefined> {
    readonly transitions: Transitions<T>;
    onTransitionStart?: OnTransitionStartFn<T, Data>;
    onTransitionEnd?: OnTransitionEndFn<T, Data>;
    onError?: OnTransitionErrorFn<T>;
}
```

<div className="members-wrapper">

### transitions

\<MemberInfo kind="property" type={`<a href='/current/core/reference/typescript-api/state-machine/transitions#transitions'>Transitions</a><T>`}   />

Defines the available states of the state machine as well as the permitted
transitions from one state to another.

### onTransitionStart

\<MemberInfo kind="property" type={`<a href='/current/core/reference/typescript-api/state-machine/state-machine-config#ontransitionstartfn'>OnTransitionStartFn</a><T, Data>`}   />

Called before a transition takes place. If the function resolves to `false` or a string, then the transition
will be cancelled. In the case of a string, the string (error message) will be forwarded to the onError handler.

If this function returns a value resolving to `true` or `void` (no return value), then the transition
will be permitted.

### onTransitionEnd

\<MemberInfo kind="property" type={`<a href='/current/core/reference/typescript-api/state-machine/state-machine-config#ontransitionendfn'>OnTransitionEndFn</a><T, Data>`}   />

Called after a transition has taken place.

### onError

\<MemberInfo kind="property" type={`<a href='/current/core/reference/typescript-api/state-machine/state-machine-config#ontransitionerrorfn'>OnTransitionErrorFn</a><T>`}   />

Called when a transition is prevented and the `onTransitionStart` handler has returned an
error message.

</div>
## OnTransitionStartFn

<GenerationInfo sourceFile="packages/core/src/common/finite-state-machine/types.ts" sourceLine="48" packageName="@vendure/core" />

Called before a transition takes place. If the function resolves to `false` or a string, then the transition
will be cancelled. In the case of a string, the string (error message) will be forwarded to the onError handler.

If this function returns a value resolving to `true` or `void` (no return value), then the transition
will be permitted.

```ts title="Signature"
type OnTransitionStartFn<T extends string, Data> = (
    fromState: T,
    toState: T,
    data: Data,
) => boolean | string | void | Promise<boolean | string | void> | Observable<boolean | string | void>
```

## OnTransitionErrorFn

<GenerationInfo sourceFile="packages/core/src/common/finite-state-machine/types.ts" sourceLine="62" packageName="@vendure/core" />

Called when a transition is prevented and the `onTransitionStart` handler has returned an
error message.

```ts title="Signature"
type OnTransitionErrorFn<T extends string> = (
    fromState: T,
    toState: T,
    message?: string,
) => void | Promise<void> | Observable<void>
```

## OnTransitionEndFn

<GenerationInfo sourceFile="packages/core/src/common/finite-state-machine/types.ts" sourceLine="75" packageName="@vendure/core" />

Called after a transition has taken place.

```ts title="Signature"
type OnTransitionEndFn<T extends string, Data> = (
    fromState: T,
    toState: T,
    data: Data,
) => void | Promise<void> | Observable<void>
```