Store

Context lives inside a machine. Some state belongs outside any one machine — shared across instances. createStore is a tiny reactive cell for exactly that: a plain value plus a listener set.

import { createStore } from '@dunky-dev/state-machine'

const store = createStore({ count: 0 })

store.get() // { count: 0 }
store.set({ count: 1 }) // shallow-merge a patch
store.set(s => ({ count: s.count + 1 })) // or an updater function
const off = store.subscribe(s => console.log(s.count))
off() // unsubscribe

No-op writes don’t notify — set compares the incoming patch against current values and skips unchanged fields.

Domain methods

Pass a second build argument to add named methods on top. build receives the base store, so the methods read/write through it:

const tooltipStore = createStore({ openId: null as string | null }, s => ({
  setOpen: (id: string | null) => s.set({ openId: id }),
  isOpen: (id: string) => s.get().openId === id,
}))

tooltipStore.setOpen('tip-1')
tooltipStore.isOpen('tip-1') // true
tooltipStore.isOpen('tip-2') // false

Bridging a store into a machine

A store is not wired into a machine’s select automatically. To make a machine react to a shared store, subscribe and forward a plain event:

machine({
  initial: 'idle',
  context: { id: 'tip-1' },
  states: {
    idle: {
      effects: [
        ({ context, send }) =>
          tooltipStore.subscribe(s => {
            send({ type: s.openId === context.id ? 'activate' : 'deactivate' })
          }),
      ],
    },
  },
})

The machine handles the event; the store drives it from outside.