Javascript State Machine

A library for finite state machines.

NOTE for existing users

VERSION 3.0 Is a significant rewrite from earlier versions. Existing 2.x users should be sure to read the Upgrade Guide.

Installation

In a browser:

1  <script src='state-machine.js'></script>

after downloading the source or the minified version

Using npm:

1  npm install --save-dev javascript-state-machine

In Node.js:

1  var StateMachine = require('javascript-state-machine');

Usage

A state machine can be constructed using:

1  var fsm = new StateMachine({
2    init: 'solid',
3    transitions: [
4      { name: 'melt',     from: 'solid',  to: 'liquid' },
5      { name: 'freeze',   from: 'liquid', to: 'solid'  },
6      { name: 'vaporize', from: 'liquid', to: 'gas'    },
7      { name: 'condense', from: 'gas',    to: 'liquid' }
8    ],
9    methods: {
10      onMelt:     function() { console.log('I melted')    },
11      onFreeze:   function() { console.log('I froze')     },
12      onVaporize: function() { console.log('I vaporized') },
13      onCondense: function() { console.log('I condensed') }
14    }
15  });

... which creates an object with a current state property:

• fsm.state

... methods to transition to a different state:

• fsm.melt()
• fsm.freeze()
• fsm.vaporize()
• fsm.condense()

... observer methods called automatically during the lifecycle of a transition:

• onMelt()
• onFreeze()
• onVaporize()
• onCondense()

... along with the following helper methods:

• fsm.is(s) - return true if state s is the current state
• fsm.can(t) - return true if transition t can occur from the current state
• fsm.cannot(t) - return true if transition t cannot occur from the current state
• fsm.transitions() - return list of transitions that are allowed from the current state
• fsm.allTransitions() - return list of all possible transitions
• fsm.allStates() - return list of all possible states

Terminology

A state machine consists of a set of States

• solid
• liquid
• gas

A state machine changes state by using Transitions

• melt
• freeze
• vaporize
• condense

A state machine can perform actions during a transition by observing Lifecycle Events

• onBeforeMelt
• onAfterMelt
• onLeaveSolid
• onEnterLiquid
• ...

A state machine can also have arbitrary Data and Methods.

Multiple instances of a state machine can be created using a State Machine Factory.

Documentation

Read more about

• States and Transitions
• Data and Methods
• Lifecycle Events
• Asynchronous Transitions
• Initialization
• Error Handling
• State History
• Visualization
• State Machine Factory
• Upgrading from 2.x

Contributing

You can Contribute to this project with issues or pull requests.

Release Notes

See RELEASE NOTES file.

License

See MIT LICENSE file.

Contact

If you have any ideas, feedback, requests or bug reports, you can reach me at jake@codeincomplete.com, or via my website: Code inComplete