A javascript finite state machine library
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Javascript State Machine

NPM version Build Status

A library for finite state machines.

matter state machine

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.


In a browser:

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

after downloading the source or the minified version

Using npm:

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

In Node.js:

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


A state machine can be constructed using:

  var fsm = new StateMachine({
    init: 'solid',
    transitions: [
      { name: 'melt',     from: 'solid',  to: 'liquid' },
      { name: 'freeze',   from: 'liquid', to: 'solid'  },
      { name: 'vaporize', from: 'liquid', to: 'gas'    },
      { name: 'condense', from: 'gas',    to: 'liquid' }
    methods: {
      onMelt:     function() { console.log('I melted')    },
      onFreeze:   function() { console.log('I froze')     },
      onVaporize: function() { console.log('I vaporized') },
      onCondense: function() { console.log('I condensed') }

... 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


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.


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

Release Notes





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