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    3.1.0 • Public • Published

    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.


    Read more about


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

    Release Notes

    See RELEASE NOTES file.


    See MIT LICENSE file.


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


    npm i javascript-state-machine

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    • jakesgordon