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: 'Loadingβ¦',
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