xsfp

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An API to use xstate in a composable way!

View API

Installation

yarn add xstate xsfp

npm install xstate xsfp

Overview

import { interpret } from 'xstate';
import * as x from 'xsfp';

// Stateless machine definition
// machine.transition(...) is a pure function used by the interpreter.

// Original way
// const toggleMachine = createMachine({
//   id: 'toggle',
//   initial: 'inactive',
//   states: {
//     inactive: { on: { TOGGLE: 'active' } },
//     active: { on: { TOGGLE: 'inactive' } },
//   },
// });

// xsfp way
const toggleEvent = targetName => x.on('TOGGLE', targetName);
const toggleState = (stateName, targetName) =>
  x.state(stateName, toggleEvent(targetName));

const toggleMachine = x.createMachine(
  x.id('toggle'),
  x.states(
    // first state is implicitly the initial state
    x.state('inactive', x.on('TOGGLE', 'active')),
    x.state('active', x.on('TOGGLE', 'inactive')),
    // composed! both are equivalent
    toggleState('inactive', 'active'),
    toggleState('active', 'inactive')
  )
);

// Machine instance with internal state
const toggleService = interpret(toggleMachine)
  .onTransition(state => console.log(state.value))
  .start();
// => 'inactive'

toggleService.send('TOGGLE');
// => 'active'

toggleService.send('TOGGLE');
// => 'inactive'

Promise example

import { interpret } from 'xstate';
import * as x from 'xsfp';

const fetchTransition = x.on('FETCH', 'loading');

const fetchMachine = x.createMachine(
  x.id('SWAPI'),
  x.context({ user: null }),
  x.states(
    x.initialState('idle', fetchTransition),
    x.state(
      'loading',
      x.invoke(
        (context, event) =>
          fetch('https://swapi.dev/api/people/1').then(res => res.data),
        x.id('fetchLuke'),
        x.onDone('resolved', x.assign({ user: (_, event) => event.data })),
        x.onError('rejected')
      ),
      x.on('CANCEL', 'idle')
    ),
    x.state('rejected', fetchTransition),
    x.finalState('resolved')
  )
);

const swService = interpret(fetchMachine)
  .onTransition(state => console.log(state.value))
  .start();

swService.send('FETCH');

Finite State Machines

import * as x from 'xsfp';

const timerTransition = targetState => x.on('TIMER', targetState);
const timerState = (stateName, targetState) =>
  x.state(stateName, timerTransition(targetState));

const lightMachine = x.createMachine(
  x.id('light'),
  x.states(
    timerState('green', 'yellow'),
    timerState('yellow', 'red'),
    timerState('red', 'green')
  )
);

const currentState = 'green';

const nextState = lightMachine.transition(currentState, 'TIMER').value;

// => 'yellow'

Hierarchical (Nested) State Machines

import * as x from 'xsfp';

const pedTimerTransition = targetState => x.on('PED_TIEMR', targetState);

const pedestrianStates = x.states(
  x.state('walk', pedTimerTransition('wait')),
  x.state('wait', pedTimerTransition('stop')),
  x.state('stop')
);

const timerTransition = targetState => x.on('TIMER', targetState);

const lightMachine = x.createMachine(
  x.id('light'),
  x.state('green', timerTransition('yellow')),
  x.state('yellow', timerTransition('red')),
  x.state('red', timerTransition('green'), pedestrianStates)
);

const currentState = 'yellow';

const nextState = lightMachine.transition(currentState, 'TIMER').value;
// => {
//   red: 'walk'
// }

lightMachine.transition('red.walk', 'PED_TIMER').value;
// => {
//   red: 'wait'
// }

Parallel State Machines

const toggleStates = (toggleEvent: string) =>
  x.states(
    x.state('on', x.on(toggleEvent, 'off')),
    x.state('off', x.on(toggleEvent, 'on'))
  );

const wordMachine = x.createMachine(
  x.id('word'),
  x.parallelStates(
    x.state('bold', toggleStates('TOGGLE_BOLD')),
    x.state('underline', toggleStates('TOGGLE_UNDERLINE')),
    x.state('italics', toggleStates('TOGGLE_ITALICS')),
    x.state(
      'list',
      x.states(
        x.state('none', x.on('BULLETS', 'bullets'), x.on('NUMBERS', 'numbers')),
        x.state('bullets', x.on('NONE', 'none'), x.on('NUMBERS', 'numbers')),
        x.state('numbers', x.on('BULLETS', 'bullets'), x.on('NONE', 'none'))
      )
    )
  )
);

const boldState = wordMachine.transition('bold.off', 'TOGGLE_BOLD').value;

// {
//   bold: 'on',
//   italics: 'off',
//   underline: 'off',
//   list: 'none'
// }

const nextState = wordMachine.transition(
  {
    bold: 'off',
    italics: 'off',
    underline: 'on',
    list: 'bullets',
  },
  'TOGGLE_ITALICS'
).value;

// {
//   bold: 'off',
//   italics: 'on',
//   underline: 'on',
//   list: 'bullets'
// }

History States

const paymentMachine = x.createMachine(
  x.id('payment'),
  x.states(
    x.state(
      'method',
      x.on('NEXT', 'review'),
      x.state('cash', x.on('SWITCH_CHECK', 'check')),
      x.state('check', x.on('SWITCH_CASH', 'cash')),
      x.historyState('hist')
    ),
    x.state('review', x.on('PREVIOUS', 'method.hist'))
  )
);

const checkState = paymentMachine.transition('method.cash', 'SWITCH_CHECK');

// => State {
//   value: { method: 'check' },
//   history: State { ... }
// }

const reviewState = paymentMachine.transition(checkState, 'NEXT');

// => State {
//   value: 'review',
//   history: State { ... }
// }

const previousState = paymentMachine.transition(reviewState, 'PREVIOUS').value;

// => { method: 'check' }

Contribution

Please feel free to make issues and PRs!

API

The API will not go into too much details, as the library expects the user to have an understanding of how xstate works.

states | parallelStates

states takes state | initialState | finalState | historyState as arguments.

parallelStates takes state | finalState | historyState as arguments.

states also accepts a string shorthand. Useful for nested states with no transitions

states('clean', 'error', 'success');

The initialState function OR the first state argument determines the initial state

states(
  initialState('initial'),
  state('second'),
  historyState('hist'),
  finalState('final')
);

state | initialState | historyState | finalState

state | initialState is a function expects that all the same arguments as createMachine.

state(
  'name',
  states(),
  parallelStates(),
  id(),
  context(),
  history(),
  on(),
  invoke(),
  entry(),
  exit(),
  after(),
  always(),
  activties(),
  meta(),
  data(),
  delimiter()
);

function finalState(stateName: string);
function historyState(
  stateName: string,
  type?: 'shallow' | 'deep' = 'shallow',
  target?: string
);

on

on is used to describe events and its transitions

function on(event: string, ...Transition);

A guard acts as the condition that determines whether the transition described before it will run

on('CLICK', 'open');

// both below are equivalent
on(
  'CLICK',
  'open',
  effect((context, event) => {
    context.refs[event.name]?.open();
  })
);
on(
  'CLICK',
  transition(
    'open',
    effect((context, event) => {
      context.refs[event.name]?.open();
    })
  )
);

// both are equiavalent
on(
  'CLICK',
  'open',
  effect((context, event) => {
    context.refs[event.name]?.open();
  }),
  guard((context, event) => {
    // if false, the effect before will not run
    return context.canOpen;
  })
);

on(
  'CLICK',
  transition(
    'open',
    effect((context, event) => {
      context.refs[event.name]?.open();
    }),
    guard((context, event) => {
      // if false, the effect before will not run
      return context.canOpen;
    })
  )
);

A guard will also implicitly act as boundaries between different transitions

on(
  'BLUR',
  'error',
  guard((context, event) => !event.value),
  // this will run only if the guard above is false
  'idle',
  assign({ value: (context, event) => event.value })
);

// transitions make this explicit
on(
  'BLUR',
  transition(
    'error',
    guard((context, event) => !event.value)
  ),
  // this will run only if the guard above is false
  transition('idle', assign({ value: (context, event) => event.value }))
);

transition

transition is a function that describes an event transition. If a target is specified, it must be the first argument.

It accepts the target state and assign | effect | action | choose | guard as arguments.

If a guard is specified it must be the last argument.

transition('idle');

transition('idle', assign({ value: (context, event) => event.value }));

transition(
  action('setValue'),
  effect((context, event) => {
    context.refs[event.name]?.focus();
  }),
  guard((context, event) => Boolean(event.value))
);

action

action is a function that accepts an action config key as the argument

action('setValue');

effect

effect is a function that accepts an action function as the argument

Also accepts a cleanup function that will be called within activities

function effect<TContext, TEvent>((context: TContext, event: TEvent) => void | (() => void))

effect((context, event) => {
  context.refs[event.name]?.focus();
});

activities(effect((context) => {
  const intervalId = setInterval(() => {
    // ...
  }, context.timeout)
  return () = {
    clearInterval(intervalId)
  }
}))

guard

guard is a function that returns a boolean. To be used within on or as the last argument of transition

function guard<TContext, TEvent>((context: TContext, event: TEvent) => boolean)

guard(context, event => Boolean(context.values[event.name]))

entry | exit | always

entry | exit | always are functions that expect the same arguments as on (minus the event name)

entry(
  'error',
  guard((context, event) => !event.value),
  // this will run only if the guard above is false
  'idle',
  assign({ value: (context, event) => event.value })
);

exit(
  'error',
  guard((context, event) => !event.value),
  // this will run only if the guard above is false
  'idle',
  assign({ value: (context, event) => event.value })
);

always(
  'error',
  guard((context, event) => !event.value),
  // this will run only if the guard above is false
  'idle',
  assign({ value: (context, event) => event.value })
);

choose

choose accepts the same arguments as transition (except for a target state) Guard acts as action boundaries as well

x.choose(
  x.action('onSave'),
  x.guard(context => Boolean(context.value)),
  // will do action below if guard is false
  x.assign({
  value: (context) => context.initialValue,
});
);

choice

choice accepts the same arguments as transition (except for a target state). Useful for explicitly setting boundaries (analogous to transition within on)

x.choose(
  x.choice(
    x.action('onSave'),
    x.guard(context => Boolean(context.value))
  ),
  // will do action below if guard is false
  x.choice(
    x.assign({
      value: context => context.initialValue,
    })
  )
);

after

after is a function that takes accepts delay arguments

after(
  2000,
  effect((context, event) => {
    context.refs[event.name]?.focus();
  })
);

after(
  (context, event) => {
    context.values[event.name] ? 2000 : 3000;
  },
  effect((context, event) => {
    context.refs[event.name]?.focus();
  })
);

delay

function delay<TContext, TEvent>(
  delay: number | ((context: TContext, event: TEvent) => number),
  ...Effects
);

invoke

invoke accepts the src type as the first argument, and onDone | onError | id | data | autoForward

x.invoke(
  (context, event) =>
    fetch('https://swapi.dev/api/people/1').then(res => res.data),
  x.id('fetchLuke'),
  x.onDone('resolved', x.assign({ user: (_, event) => event.data })),
  x.onError('rejected')
);

id

id is a function that takes a string

function id(id: string);

context

context is a function that takes the context of the machine or a function that returns the context of the machine

function context<TContext>(context: TContext | () => TContext)

history

history is a function that takes the history types

function history(type: 'shallow' | 'deep' | 'none');

merge

merge accepts on OR assign | action | effect and merges them

const reset = merge(
  assign({
    value: '',
  }),
  assign({
    open: false,
  })
  // ignores function assignment
  assign((context) => ({
    open: !context.open
  }))
);

const resetTransitions = merge(on('reset', reset), on('cancel', reset));