@ue-too/being / index / extendState

Function: extendState()

extendState<E, C, S, O>(original, extension): State<E, C, S, O>

Defined in: expansion.ts:231

Builds a state for a wider machine out of an existing state plus additions.

Type Parameters

E

E

C

C extends BaseContext

S

S extends string

O

O extends Partial<Record<keyof E, unknown>> = DefaultOutputMapping<E>

Parameters

original

ExtendableState

extension

StateExtension<E, C, S, O>

Returns

State<E, C, S, O>

Remarks

Everything the original exposes through the State interface is inherited: reactions, guards, event guards, preconditions, delay and the enter/exit hooks. The extension merges over that, so an entry with the same event name replaces the inherited one. Use the function form of eventReactions when an override needs to call the inherited action. A _defer on the original is not carried over because the State interface does not expose it.

The target generics are usually inferred from the registration site; name them explicitly when they are not.

Example

const idle = extendState<ExpEvents, ExpContext, ExpStates, ExpOut>(new KmtIdleState(), {
    eventReactions: inherited => ({
        scroll: scaleZoom(inherited.scroll),
        leftPointerDown: { action: startPlacement, defaultTargetState: 'PLACEMENT' },
    }),
    uponEnter: (context, _m, _from, inherited) => {
        inherited();
        context.reapplyHoverCursor();
    },
});