Creating Finite State Machines with VivaGraph.js

fsm.js

/*******************************************
 * Usage:
 *
 * var fsm = new FiniteStateMachine(),
 *
 * fsm.from('state1')
 *   .goTo('state2').when(regex1)
 *   .goTo('state3').when(regex2);
 * fsm.from('state2')
 *   .goTo('state2').when(regex2);
 *
 * fsm.start('state1') // Defining starting state is state1
 * // running string input through FSM.
 * for (var i = 0; i < input.length; ++i) {
 *  if (fsm.step(input[i])) { all is good, state is valid } else { invalid input }
 */

var FiniteStateMachine = function() {
    this.graph = Viva.Graph.graph();
};

FiniteStateMachine.prototype = {
    from : function (fromStateName) {
        var that = this,
            stateDescription = {
                goTo : function(toStateName) {
                    return {
                        when : function (predicate) {
                            that.graph.addLink(fromStateName, toStateName, predicate);
                            return stateDescription;
                        }
                    };
                }
            };
        return stateDescription;
    },
    start : function (startState) {
        this.currentNode = this.start = startState;
    },
    reset : function () {
        this.currentNode = this.start;
    },
    step : function (input) {
        var links = this.graph.getLinks(this.currentNode),
            result = false;
        for(var i = 0; i < links.length; ++i) {
            if (links[i].fromId === this.currentNode && this.predicate(links[i].data, input)) {
                this.currentNode = links[i].toId;
                result = true;
                break;
            }
        }
        return result;
    },
    predicate : function(linkPredicate, input) {
        // assuming linkPredicate is a regex, but could be anything in future:
        return linkPredicate.test(input);
    }
};

Really good looking piece of code.