2.1.0 • Public • Published

Fsm-hub (@peter.naydenov/fsm-hub)

FSM orchestration and state managment tool.

Did you have tried Fsm (@peter.naydenov/fsm) till now? Fsm-hub extends reactivity control to this eco-system. Fsm-hub will listen for changes in all hub's registrated machines(fsm) and will trigger an execution of callback code - listener functions or update with action in other fsm machines. Register all fsm machine instances and form an application with centralized control of the logic.

Fsm-hub Description Object

Fsm-hub's description is an object that contains information about how the hub should work. Description contains reactivity and transformation tables. Provide the description object during the hub creation process.

const hub = new FsmHub ( description, transformerLibrary )

TransformerLibrary is an object with functions used in transformation process described later in this document.


Fsm-hub reactivity is described as a table. Every single row describes single reactivity-reaction. Remember that reactivity reaction is always an array. Reactivity is part of fsm-hub description object.

Reactivity-Reaction with 3 Elements

Reaction on state-change with listener function. The row has 3 elements:

[ 'machine', 'open', 'listenerFn']

Read it as: When fsm machine change it status to open then execute the function listenerFn.

Reactivity-Reaction with 4 Elements

Reaction on state-change with update-action in another fsm. The row contains 4 elements:

[ 'machine', 'open', 'camera', 'wake' ]

Read it as: When fsm machine change it status to open then fsm camera should trigger update with action wake.

Reactivity Rules

Execution of reactivity reactions goes always from top to bottom by type. Fsm-hub will execute fsm updates first and then will trigger the listener functions. Example:

    [ 'machine', 'open', 'informSecurity' ]
    [ 'machine', 'open', 'activateLights' ]
    [ 'machine', 'open', 'camera', 'wake' ]

Order of execution:

  1. Will trigger fsm update of the camera fsm with action wake.
  2. Will trigger listener function informSecurity.
  3. Will trigger listener function activateLights.

Description\Transformers (not required)

Transformers take care of data-compatibility across the hub. Fsm machines registrated to the hub could vary in their update-results data structures. Transformers can apply data-model where is needed. Example:

    //    from/to     :  functionName
      'oneFsm/twoFsm' : 'one2two'
    , 'twoFsm/showme' : 'simple' 

Read as:

  • Row 1: Listener twoFsm will use transformer function one2two for results of state-changes in oneFsm;
  • Row 2: Listener showme will use transformer function simple for results of state-changes in twoFsm;

Transformer functions are defined in transformerLibrary object, that is provided as second parameter during hub-creation. Missing transformer means that the result of update will be provided to the listener without modifications. Transformers are available for both type of listeners: fsm machines and functions.

Transformer functions

Transformer function are receiving two arguments - fsm state after update and result from response object. Transformer response is provided to the listener as an argument.

 const transformerLib = {
     one2two ( stateUpdate, result ) { // stateUpdate is the state of fsm, result is from fsm transition response.
                switch ( status ) {
                    case 'none' :
                                return result   // ...in case of state 'none': Provide result to the listener without changes
                    case 'active':
                                let x;
                                if ( result == 'none' )   x = {name: 'abc', project: 'undefined' }
                                else                      x = { name: result.name, project: result.project }
                                return x
                                return false
                } // switch status
        } // one2two func.
 } // transformerLib


   constructor  : 'Create the hub. Provide hub-description object and transformation'
 , addFsm       : 'Register fsm instances to the hub'
 , addFunctions : 'Register callback function to the hub'


Create hub and register two fsm machines: oneFsm and twoFsm. Register also a callback function showme.

Hub should start twoFsm when oneFsm is started. When twoFsm is active trigger a showme callback function. The transformer twoFsm/showme should be applied.

// Define Fsm machines
         miniOne = {
                          init : 'none'
                        , table : [
                                    [ 'none', 'activate', 'active', 'switchOn']

// Setup fsm transition libraries
    const transitionOne = {
                    switchOn ( task, dependencies, stateObj, dt ) {
                                task.done ({ 
                                          success  : true 
                                        , response : dt   // send data without changes

// Init fsm machines
    const  // oneFsm and twoFsm are identical fsm machines
          one = new Fsm ( miniOne, transitionOne  )
        , two = new Fsm ( miniOne, transitionOne  )

// Define hub
        machine = {
                        reactivity : [
                                    //    [ fsm, onStateChange, listenerFsm , action  ]
                                          [ 'one', 'active', 'two', 'activate'  ]
                                    //    [ 'fsm',     'state', 'callbackFn' ]
                                        , [ 'two', 'active', 'showme' ]
                        , transformers : {
                                        // "from/to" : functionName
                                        'two/showme' : 'simple'
      , transformerLib = {
                        simple : function ( state, resultResponseData ) {
                                        return {
                                                  second : 'second'
                                                , state
                                                , 'answer' : resultResponseData.response

// Initialize the hub
    let hub = new FsmHub ( machine, transformerLib );

    function showme (transitionResult) {
                console.log ( 'ShowMe' )
                console.log ( transitionResult.answer )
        } // showme func.

    hub.addFsm ({ one, two })
    hub.addFunctions ( { showme })

// Start!
    oneFsm.update ( 'activate', { response:'try'} )

// Result on the screen:
// ShowMe
// { second: 'second', state: 'active', answer: 'try' }



'@peter.naydenov/fsm-hub' was created by Peter Naydenov.


'@peter.naydenov/fsm-hub' is released under the MIT License.

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