JSPM

 _  _  _ _    _  
|_)(_)_)_)|_|||| 
| state machine

I am able.

• From potis (“able, capable”) + sum (“I am”).

Inspiration

API inspiration from machina.js. Thanks to Jim Cowart and contributors for formulating a powerful api.

Install

npm install --save possum

Building

make build

Example

make example

Roadmap

• Hierarchical State Machine support
• Behavior tree generation (ala machine.js).
• Separate config from actor

Module Support

Works in nodejs and the browser using CJS modules. For the browser maybe use browserify. AMD isn't going to be supported, sorry.

Getting Started

This is in the app.js for the example.

//listening to Kiss' Love Gun on my record player

//first, define our state machine spec

var gun = {
    namespace: 'kiss'
    ,initialState: 'uninitialized'
    ,enable: function(actions) {
        Object.keys(controls).forEach(function(key){
            controls[key].setAttribute('disabled','disabled')
        })
        if(!actions || !actions.length) {
            return
        }
        actions.forEach(function(action){
            controls[action].removeAttribute('disabled')
        })
    }
    ,states: {
        'uninitialized': {
            _onEnter: function(){
                this.enable(['initialize'])
                return this.recordPlayer.turnOn()
            }
            ,'initialize': function(args) {
                return this.recordPlayer.spinRecord()
                    .then(this.transition.bind(this,'initialized'))
            }
        }
        ,'initialized': {
            _onEnter: function(){
                this.enable(['pullTrigger','load'])
            }
            ,'pullTrigger': function() {
                this.deferUntilTransition('aimed')
            }
            ,'load': function(args) {
                this.deferUntilTransition('loading')
                return this.transition('loading')
            }
        }
        ,'loading': {
            _onEnter: function(){
                this.enable(['load'])
            }
            ,'load': function(args) {
                this.loadWeapon(args && args.bullets)
                return this.transition('loaded')
            }
            ,'reload': function() {
                return this.handle('load')
            }
        }
        ,'loaded': {
            _onEnter: function(){
                document.querySelector('.remaining').innerHTML = ''
                this.enable(['aim'])
            }
            ,'aim': function(args) {
                this.song = (args && args.target) || this.bullets.shift()
                this.recordPlayer.hoverNeedleOver(this.song)
                return this.transition('aimed')
            }
        }
        ,'aimed':{
            _onEnter: function(){
                this.enable(['pullTrigger'])
            }
            ,'pullTrigger': function() {
                return this.fire()
                    .then(this.transition.bind(this,'smoking'))
            }
        }
        ,'smoking': {
            _onEnter: function(){
                console.log('light cigarette, sit back and relax')
                this.enable(['liftNeedle'])
            }
            ,'aim': function(args){
                this.deferUntilNextHandler()
                return this.handle('liftNeedle')
            }
            ,'liftNeedle': function(){
                if(this.bullets.length) {
                    return this.transition('loaded')
                }
                return this.transition('emptied')
            }
        }
        ,'emptied': {
            _onEnter: function(){
                this.enable(['reload'])
                return this.handle('aim')
            }
            ,'aim': function(args){
                return this.recordPlayer.returnArm()
            }
            ,'reload': function(){
                this.deferUntilTransition('loading')
                return this.transition('loading')
            }
        }
    }
    ,loadWeapon: function(bullets){
        return this.bullets = bullets || [
            'I Stole Your Love'
            ,'Shock Me'
            ,'Love Gun'
        ]
    }
    ,fire: function(){
        //asynchronous, returns a Promise
        return this.recordPlayer.play(this.song)
    }
}

//now pass the spec to possum to get a prototype
var model = possum(spec).create() // model.state === undefined

model.start().then(function(){
    console.log(model.state) // ->'uninitialized'
})

What is a Possum?

A marsupial.

But for our purposes, possum uses stampit under-the-hood for model prototyping.

This means that when you do this:

var model = possum(spec)

what you get is a 'stamp' that allows to to:

model
.state({ prop: 'erty'})
.methods({ meth: function isBad(){..}})
.enclose(function(){
    var secretData = 'shhhh'
    this.prop == 'erty' // -> true
})
.create() //this creates the possum instance; you may also just call it as a function

Extending a possum

Sometimes you may want to merge two spec objects into a single instance. Ideally, this is the burden of the calling code but possum exposes an extend function to assist with this form of composition. Note that will overwrite states of the same name with this procedure. If you want fancier mixing then prepare the input spec object before passing it to possum.

var spec = {
    initialState: 'foo'
    ,states: {
        'foo': {
            ...
        }
    }
}
var disposable = {
    states: {
        'disposed': {
            _onEnter: function(){
                this.disposed = true
            }
        }
    }
}
var model = possum(spec).extend(disposable).create()
model.transition('disposed') // model.disposed === true

Asynchronous transitions and handlers

We needed asynchronous support for transitioning to states and for input handlers found on states.

Due to asynchronous _onEnter callback potential, a possum must invoke .start() to be properly initialized.

This allows separation between construction and initialization.

Possum Spec API

namespace {String} [optional]

The namespace for this instance

initialState {String} required

The state to transition to when .start() is called

states {Object} required

The states configuration in the shape of:

var states = {
    'myState': {
        _onEnter: function(){
            //optional
            //steps to perform right when entering a state
            //can return an Promise for async support
        }
        ,'doIt': function(args) {
            //handle the command 'doIt'
            //receiving exactly ONE argument
            return this.doIt()
        }
        ... 
        ,_onExit: function() {
            //optional
            //steps to perform right before transitioning
            //out of this state
        }
    }
}

Note that each state's input handler, will receive one argument. That means you must invoke the handlers this way:

model.handle('doIt','myArgument')

Additional arguments will be ignored.

handlers {Array} [optional]

Provide handler objects can be in the form of :

var handler = {
    name: 'myHandler'
    ,fn: function(args) {
        // just like any other handler
    }
    ,match: function(spec) {
        //spec.inputType is the input type being invoked
        //spec.state is the current state of the possum instance
        return true/false
    }
}

Or, you may provide wildcard handlers in the form of :

var handler = { '*': function(args) { //just like any other handler } }

The order of execution for matching handlers is:

1. Wildcard handlers
2. Handlers configured through handlers collection that match (not through state config)
3. State input handler

Possum Instance API

state {String}

The current state of the possum instance. This is undefined until the instance has been .start()-ed.

priorState {String}

The priorState state of the possum instance, if any. This is undefined until a transition has occurred.

handle(inputType, args) {Function}

Queues the command inputType and processes it with the singular args payload. Note that only one argument will be used. Other arguments will be ignored.

Returns a Promise resolving the context.

transition(toState) {Function}

Convenience method that queues the transition commands _onExit, _transition, and _onEnter and processes them.

Returns a Promise resolving the context.

start {Function}

Causes a transition to the initialState.

Returns a Promise, resolving when transition has completed.

deferUntilTransition(toState) {Function}

Queues the current message (input) to be replayed after the possum has transitioned to toState. If toState is not provided, then it will replay after any transition has occurred.

Returns this possum instance.

deferUntilNextHandler {Function}

Queues the current message (input) to be replayed after the possum has handled another input, regardless of whether a transition has occurred. Note: be careful that you avoid infinite loops using this functionality.

Returns this possum instance.

current {Function}

Returns an processContext which exposes:

• currentMessage {Function} The message currently being handled
• completed {Boolean} A flag indicating if the processing has completed

This is really for internal use, but you may use this inside a handler to get access to the current message being invoked.

Possum Events

handled

Emitted just after an input handler has been invoked but probably before the handler has completed (asynchronously).

Event properties:

• topic: 'handled'
• inputType: {String} the name of the handler you just called
• payload: {Any} The arguments passed into the handle call
• action: {String} the path of the handler you just called ; eg 'myState.myHandler'

completed

Emitted after an input handler Promise has resolved.

Event properties:

• topic: 'completed'
• inputType: {String} the name of the handler you just called
• payload: {Any} The arguments passed into the handle call
• action: {String} the path of the handler you just called ; eg 'myState.myHandler'

transitioned

Emitted after a possum has transitioned into a state, but before its entry callback has been invoked (_onEnter).

Event properties:

• topic: 'completed'
• inputType: {String} the name of the handler you just called
• payload: {Object} having these properties
  • toState The state you just transitioned to
  • fromState The state you just transitioned from
• action: {String} the path of the handler you just called ; eg 'myState.myHandler'

noHandler

Emitted when an input has been attempted on a state that does not declare it.

invalidTransition

Emitted when an transition is attempted to a state that does not exist.

Diagnostics

possum likes to talk alot using the debug npm module. To enable logging, drop into your console and type localStorage.debug = 'possum*'. To turn it back off, type localStorage.debug = undefined. In node, you can pass DEBUG=possum* as an environment variable.

Tests

make test will by default run tests on Safari, Chrome, Firefox, and NodeJS.

You can also do make node to quickly run tests or make silent node to shut possum up during test runs.

Credits

• machina.js
• ascii generation