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nanostate
Advanced tools
Small Finite State Machine implementation
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Readme
Small Finite State Machines. Great data structure to make code more readable, maintainable and easier to debug.
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'
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'
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' }
}))
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'
// }
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'))
}
}
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'
.
$ npm install nanostate
FAQs
Small Finite State Machine implementation
The npm package nanostate receives a total of 24 weekly downloads. As such, nanostate popularity was classified as not popular.
We found that nanostate demonstrated a not healthy version release cadence and project activity because the last version was released a year ago. It has 2 open source maintainers collaborating on the project.
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