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javascript-state-machine v3.1.0

A finite state machine library

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:

  • - 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, or via my website: Code inComplete

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