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Finite State Machine library Uses node-graph to work with state graph.

Meanwhile, you can look at test/test.js to see usage example.


npm install node-fsm


new FSM(machineSpec, routerFunc)

machineSpec should contain state graph (nodes and edges like in node-graph). Additional properties are currentState that contains name of current machine state. data contains your arbitrary data tied with fsm.

routerFunc(edge, requestData, callback) is async function that checks, whether we made our transition successfully, or not. First argument is an edge object represents state graph edge we attempt to follow (hint: here you can process any arbitrary data you put on edge object in state graph). At the routerFunc completion you should call callback, passing err object, if you encountered any errors, and boolean variable that indicates whether we made transition or not. routerFunc is bound to fsm instance, so you can use this variable to access machine object.

var machineSpec = {
    nodes: [
            name: 'A'
            name: 'B',
            youCanPutArbitraryDataOnYourNodes: { ... }
    edges: [
            name: 'A->B',
            from: 'A',
            to: 'B',
            youCanPutArbitraryDataOnYourEdgesToo: { ... }
    currentState: 'A',
    data: { … }
var routerFunc = function (edge, requestData, callback) {
    // Make any external calls to determine,
    // whether our transition is succesfull or not
    // …
    callback(null, true);
var fsm = new FSM(machineSpec, routerFunc);


Returns array of edges, that can be followed from current machine state.

    var edges = fsm.availableEdges();
    // Returns:
            name: 'A->B',
            from: 'A',
            to: 'B',
            youCanPutArbitraryDataOnYourEdgesToo: { ... }

follow(edgeName, [requestData], callback)

Attempt to change machine state following edge specified by edgeName and optional requestData that would be passed to routerFunc (useful, since it can provide addtional info on change state attempt without modifying any of fsm data). If you omit requestData argument, your routerFunc will receive null value as a second argument. Callback should take two arguments (err, status), where err will contain any errors encountered during attempt to change state, and status will contain boolean value indication whether attempt was successful, or not.


Returns instance of node-graph Graph object that you could use to navigate across fsm state graph. See docs for node-graph for methods reference.


emit('state', edge)

When we successfully made a transition to a new state, fsm instance emits 'state' event, passing edge we followed as argument. While edge object contains both from and to fields, you can figure out, what was previous state.

emit('terminal', edge)

When we successfully made a transition to a new state, and this state is terminal (there is no edges outbound for current state) fsm instance emits 'terminal' event, passing edge we followed as argument.



Now .follow() takes requestData as a second argument, containing data that will be passed to routerFunc without altering fsm. This change is backward incompatible — you should update your routerFunc to take three arguments (see docs on routerFunc earlier).