simple state machine

state-machine.js

(function(){

var State = function(name) {
  this.name = name;
};

State.prototype.from = function(from) {
  this.from_ = from;
  return this;
};

State.prototype.to = function(to) {
  this.to_ = to;
};

State.prototype.can = function(from, to){
  if(Array.isArray(this.from_)) {
    return !!~this.from_.indexOf(from) && to === this.to_;
  } else {
    return from === this.from_ && to === this.to_;
  }
};

window.KeyMaster = {
  events: {},
  _callbacks: {},

  add : function(evt){
    this.events[evt] = new State(evt);
    this[evt] = function(){
      return this.transition.apply(this, arguments);
    }.bind(this, evt);
    return this.events[evt];
  },

  transition : function(evt) {
    if(!this.current)
      throw "not initialized";
    if(!this.events[evt].can(this.current, this.events[evt].to_))
      return this.current + " can't transition to " + this.events[evt].to_;
    if(!this.events[evt])
      throw "unknown transition " + evt;

    this._call.apply(this, arguments);
  },

  on : function(e, fn){
    var callbacks = (this._callbacks[e] || (this._callbacks[e] = []));
    callbacks.push(fn);
  },

  initial : function(key){
    if(this.current) throw "Already initialized";
    this.current = key;
  },

  _call : function(evt){
    var before, after, args = [].slice.call(arguments, 1, arguments.length);

    this._trigger.apply(this, ['before:' + evt, evt].concat(args));
    this.current = this.events[evt].to_;
    this._trigger.apply(this, ['after:' + evt, evt].concat(args));
  },

  _trigger : function(e){
    var callbacks = this._callbacks[e];
    if(!callbacks) return;
    for(var i = 0; i < callbacks.length; i++)
      callbacks[i].apply(this, arguments);
  }
};

})();


// tests
KeyMaster.add('warn').from('green').to('yellow');
KeyMaster.add('panic').from('yellow').to('red');
KeyMaster.add('calm').from('red').to('yellow');
KeyMaster.add('clear').from('yellow').to('green');
KeyMaster.initial('green');

KeyMaster.warn();
KeyMaster.panic();
KeyMaster.calm();
KeyMaster.clear();