nanostate

Small Finite State Machines. Great data structure to make code more readable, maintainable and easier to debug.

Usage

var nanostate = require('nanostate')

var machine = nanostate('green', {
  green: { timer: 'yellow' },
  yellow: { timer: 'red' },
  red: { timer: 'green' }
})

machine.emit('timer')
console.log(machine.state)
// => 'yellow'

machine.emit('timer')
console.log(machine.state)
// => 'red'

machine.emit('timer')
console.log(machine.state)
// => 'green'

Hierarchical

Let's implement a traffic light that flashes red whenever there's a power outage. Instead of adding a powerOutage event to each normal state, we introduce a hierarchy which allows any normal state to emit the powerOutage event to change the state to flashingRed.

var nanostate = require('nanostate')

var machine = nanostate('green', {
  green: { timer: 'yellow' },
  yellow: { timer: 'red' },
  red: { timer: 'green' }
})

machine.event('powerOutage', nanostate('flashingRed', {
  flashingRed: { powerRestored: 'green' }
}))

machine.emit('timer')
console.log(machine.state)
// => 'yellow'

machine.emit('powerOutage')
console.log(machine.state)
// => 'flashingRed'

machine.emit('powerRestored')
console.log(machine.state)
// => 'green'

History (to be implemented)

Implementers note: keep track of the last state a machine was in before exiting to the next machine. That way if '$history' is called, it can be merged into the previous machine.

TODO: figure out how it works if machines are combined in a non-linear fashion.

var nanostate = require('nanostate')

var machine = nanostate('cash', {
  cash: { check: 'check' },
  check: { cash: 'cash' }
})

machine.join('next', nanostate('review', {
  review: { previous: '$history' }
}))

Parallel

Sometimes there's multiple parallel states that need expressing; nanostate.parallel helps with that. For example when editing text, a particular piece of text might be bold, italic and underlined at the same time. The trick is that all of these states operate in parallel

var nanostate = require('nanostate')

var machine = nanostate.parallel({
  bold: nanostate('off', {
    on: { 'toggle': 'off' },
    off: { 'toggle': 'on' },
  }),
  underline: nanostate('off', {
    on: { 'toggle': 'off' },
    off: { 'toggle': 'on' },
  }),
  italics: nanostate('off', {
    on: { 'toggle': 'off' },
    off: { 'toggle': 'on' },
  }),
  list: nanostate('none', {
    none: { bullets: 'bullets', numbers: 'numbers' },
    bullets: { none: 'none', numbers: 'numbers' },
    numbers: { bullets: 'bullets', none: 'none' }
  })
})

machine.emit('bold:toggle')
console.log(machine.state)
// => {
//   bold: 'on',
//   italics: 'off',
//   underline: 'off',
//   list: 'none'
// }

Nanocomponent

Usage in combination with nanocomponent to create stateful UI components.

var Nanocomponent = require('nanocomponent')
var nanostate = require('nanostate')

module.exports = class Component extends Nanocomponent {
  constructor (name, state, emit) {
    super(name, state, emit)

    this.state = {
      data: {},
      input: ''
    }

    this.machine = nanostate('idle', {
      idle: { click: 'loading' },
      loading: { resolve: 'data', reject: 'error' },
      data: { click: 'loading' },
      error: { click: 'loading' }
    })

    this.machine.on('loading', () => this.searchRepositories())
  }

  createElement () {
    var buttonText = {
      idle: 'Fetch Github',
      loading: 'Loading…',
      error: 'Github fail. Retry?',
      data: 'Fetch Again?'
    }[this.machine.state]

    return html`
      <div>
        <input
          type="text"
          value=${this.state.input}
          onChange=${e => (this.state.input = e.target.value) && this.rerender()}
        >
        <button
          onClick=${() => this.machine.emit('click')}
          disabled=${this.machine.state === 'loading'}
        >
          ${buttonText}
        </button>
        ${data && html`<div>${JSON.stringify(data, null, 2)}</div>`}
        ${this.machine.state === 'error' && html`<h1>Error</h1>`}
      </div>
    `
  }

  searchRepositories () {
    fetch(`${ROOT_URL}/${this.state.input}`)
      .then(res => res.json())
      .then(res => {
         this.state.data = res.data
         this.machine.emit('resolve')
       })
      .catch(err => this.machine.emit('reject'))
  }
}

API

machine = nanostate(initialState, transitions)

Create a new instance of Nanostate. Takes the name of the initial state, and a mapping of states and their corresponding transitions. A state mapping is defined as { 1: { 2: 3 }}, where 1 is the state's name, 2 is an event name it accepts, and 3 is the new state after the event has been emitted.

machine.emit(event)

Move from the current state to a new state. Will throw if an invalid command is passed.

machine.on(state, cb)

Trigger a callback when a certain state is entered. Useful to trigger side effects upon state change.

state = machine.state

Return the current state.

machine.event(eventName, machine) (to be implemented)

Add another machine to the transition graph. The first argument is an event name, which can be transitioned to from all other states in the graph.

machine = nanostate.parallel(machines) (to be implemented)

Combine several state machines into a single machine. Takes an object of state machines, where the key is used to prefix the events for the state machine.

Say we have two state machine: 'foo' and 'bar'. 'foo' has an event called 'beep'. When combined through .parallel(), the event on the combined machine would be 'foo:beep'.

Installation

$ npm install nanostate

See Also

• Infinitely Better UIs With Finite Automata (video)
• yoshuawuyts/fsm-event
• davidkpiano/xstate

License

Apache-2.0