State Transition System

Use this module to create infinite-state-machines. A State Machine defines transition rules, which comprise a from state, a to state, and n array of functions to call when the machine transitions between those states. For example, you could have a rule, from 'loading' to 'idle' you call render().

Usage

Require the module and then instantiate however many state machines you need. The first and only argument is an initialState (defaults to 'null').

var StateMachine = require('state-transition-system')
var sm = new StateMachine('woo')

You then add transitions with the addTransition function.

sm.addTransition('woo', 'wee', function(){...})

Finally, change the state of the machine with sm.changeState()

sm.changeState('wee') // ... executes.

You can add multiple transitions in 1 call

sm.addTransition('woo', 'waa', function(){...}, function(){...})

You can add multiple transitions in multiple calls

sm.addTransition('woo', 'waa', function(){...})
sm.addTransition('woo', 'waa', function(){...})
sm.addTransition('woo', 'waa', function(){...})

It will find all functions that match a state change and execute them first-in first-out.

If any matching transition function returns false, the transition will be cancelled and will emit a transitionblocked event.

sm.addTransition('woo', 'waa', function() { return false })
sm.addTransition('woo', 'waa', function() { console.log('never reached') })

State Rules

There is some wildcard logic in state rules. '*' will match any state, and '*!waa' will match any state except 'waa'. You can chain more exclusions as you wish, for example '*!waa!wuu'.

By adding wildcards, it means multiple transitions could be valid for a single state change. In these cases, it will execute all transitions in the order that they were added to the state machine with addTransition()

Example

var StateMachine = require('state-transition-system')
var sm = new StateMachine('woo')
 
sm.addTransition('woo', 'wee', function() { console.log('nice') })
sm.addTransition('wee', 'waa', function() { console.log('one!') })
sm.addTransition('woo', '*!wee', function() { console.log('excluded') })
 
sm.changeState('wee') // 'nice!'
sm.changeState('waa') // 'one!'
sm.changeState('woo') // nothing, because no transition matches
sm.changeState('waa') // 'excluded'

Events

State Machine instances are node EventEmitters. As such they provide the EventEmitter API as well. Two events are emitted as the states change. Firstly, 'changestate', and 'changestate:<name>''.

changestate

Event that fires when state is changed. First argument to any callbacks is the state, subsequent arguments are those passed into the changeState call.

changestate:<name>

Event that fires when a state is changed. Includes the name of the state in the event name. Arguments match those passed into the changeState() call.

transitionblocked

Event that fires when any statechange is blocked. First argument to any callbacks is the state, subsequent arguments are those passed into the changeState call. The final argument is a reference to the function which blocked the transition as it is useful for debugging.

transitionblocked:<name>

Event that fires when a named statechange is blocked. Includes the name of the state in the event name. Arguments match those passed into the changeState() call. The final argument is a reference to the function which blocked the transition as it is useful for debugging.

API

new StateMachine(initialState)

Construct a state machine with an initial state of initialState.

sm.addTransition(from, to, fn[, fn, ...])

Adds a transition to a state machine. When the state machine transitions from from to to then fn will be called. The first two arguments to fn will be from and to, subsequent arguments will match those passed in when changeState is called.

sm.changeState(state)

Changes the state machines state to state. Any transitions that have been registered that match the transition will be called.

Changelog

• 2.0.0: If any transition functions return false, cancel the transition