Basic State Machine for Javascript objects

basic_fsm.js

//++++++++++++++++++++++++++++++++++++++++++++++++
// Basic FSM implementation
//++++++++++++++++++++++++++++++++++++++++++++++++
var StateMachine = function(initial_state) {

  var transitions = {},
  state_callbacks = {enter:{}, exit:{}},
  addTransition = function (from, to, guard) {
    transitions[from] = transitions[from] || {};
    transitions[from][to] = guard || function () {return true};
  },
  addCallback = function (clbk, state, handler) {
    state_callbacks[clbk][state] = state_callbacks[clbk][state] || [];
    state_callbacks[clbk][state].push(handler)
  },
  runCallbacks = function (obj, clbk, state, other_state) {
    var b = state_callbacks[clbk][state];
    if(!b) return true;
    for(var i=0;i<b.length;i++){
      b[i].apply(obj, [other_state]);
    }
  }

  return {
    state: initial_state,

    onStateChange: function (state) {
      return true;
    },

    transition: function (from, to, guard) {
      addTransition(from, to, guard);
      return this;
    },

    enter: function (state, handler) {
      addCallback('enter', state, handler);
      return this;
    },

    exit: function (state, handler) {
      addCallback('exit', state, handler);
      return this;
    },

    goTo: function (new_state) {
      var from = transitions[this.state];
      var to = from ? from[new_state] : false;
      if(!to){
        throw 'No transition defined from "'+this.state+'" to "'+new_state+'"';
      }
      if(to()) { // run guard function
        runCallbacks(this, 'exit', this.state, new_state);
        runCallbacks(this, 'enter', new_state, this.state);
        this.state = new_state;
        this.onStateChange(new_state);
        return true;
      } else {
        return false;
      }
    }

  }
}


//++++++++++++++++++++++++++++++++++++++++++++++++
// USAGE
//++++++++++++++++++++++++++++++++++++++++++++++++

function exampleGuard() {
  console.log('RUNNING GUARD'); 
  return true; // false to deny transition  
}

var Connection = function(){}
Connection.prototype = StateMachine('closed');

var conn = new Connection();

conn.onStateChange = function(state){console.log('SUCCESSFUL STATE CHANGE TO ', state)}

conn
//+++++++++++++++++++++++++++++++++++++++++++++
// TRANSITIONS
//+++++++++++++++++++++++++++++++++++++++++++++
.transition('closed',     'failed'     )
.transition('closed',     'connecting', exampleGuard)
.transition('connecting', 'unavailable' )
.transition('connecting', 'connected'   )
.transition('unavailable','connected'   )
.transition('connected',  'unavailable' )
//+++++++++++++++++++++++++++++++++++++++++++++
// CALLBACKS
//+++++++++++++++++++++++++++++++++++++++++++++
.exit('closed', function (to) {
  console.log('EXITING closed TO ', to);
})
.enter('connecting', function (from) {
  console.log('ENTERING connecting FROM ', from);
})
.exit('connecting', function (to) {
  console.log('EXITING connecting TO ', to);
})

try{
  conn.goTo('connected');
} catch(e) {console.log(e, 'CURRENT STATE IS', conn.state)}

conn.goTo('connecting');

console.log(conn.state);