Actions

Actions are fire-and-forget functions that run on a transition. They receive { context, setContext, event, send, computed } and run in order.

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

const m = machine({
  initial: 'idle',
  context: { saved: false },
  states: {
    idle: {
      on: {
        save: {
          actions: [$ => $.setContext({ saved: true }), $ => console.log('saved!')],
        },
      },
    },
  },
})

act() — write-sugar

act() is shorthand for a context-writing action — drops the $ => $.setContext(...) wrapper. Takes one or many patches (applied in order; a later patch function sees earlier writes):

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

on: {
  save:  { actions: act({ saved: true }) },
  bump:  { actions: act({ touched: true }, $ => ({ n: $.context.n + 1 })) },
}

entry / exit

Run actions whenever a state is entered or left — regardless of which transition triggered it:

states: {
  open: {
    entry: ['focusFirstItem'],
    exit:  ['restoreFocus'],
    on: { close: { target: 'closed' } },
  },
  closed: {},
}

oneOf() — conditional actions

Pick one branch of actions by guard. First passing branch wins; a guardless branch is the fallback:

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

actions: [
  oneOf(
    { guard: 'isMobile', actions: 'lockScroll' },
    { guard: 'isDesktop', actions: 'dimBackground' },
    { actions: 'noop' }, // guardless = fallback
  ),
]

Named actions

Reference an action by string and define it in implementations.actions:

machine({
  initial: 'idle',
  context: {},
  states: {
    idle: {
      on: { ping: { actions: 'notify' } },
    },
  },
  implementations: {
    actions: {
      notify: () => console.log('ping!'),
    },
  },
})