State Machine Class

State Machine Class is a generic state machine that can be used on its own or as a base class to create objects that must cleanly transitoin between states.

Usage

Installation

npm install --production state-machine-class
# use "--production" to avoid installing unnecessary development dependencies

In Program

const StateMachine = require("state-machine-class");
const transitions = {...};// List of permitted transitions between states.
const defaultState = "...";// Default state in which to start;
const cleanup = function(current){//Cleanup function
    this...
}
export default class extends StateMachine{
    constructor(){
        super(transitions, defaultState, cleanup);
    }
}

API

Constructor

new StateMachine(transitions, defaulltState, cleanup, dieOnError, events);

transitions:Object

The transition object represents avaliable transitions between states.

Truthy transitions

The ability to transition between states is defined by the truthiness of values in the transitions objects. Given state1 and state2, and a transition object transitions, a transition is only allowed if the value of of transitions[state1][state2] is truthy.

Example: Samptle transitons object

const transitions = {
    "first-state":
    {
        "second-state":true,
        "third-state":true
    },
    "second-state":{
        "third-state":true
    }
}

In the above example, the state machine may be transion:

- from "first-state" to "second-state" (transitions["first-state"]["second-state"] === true)
- from "first-state" to "third-state" (transitions["first-state"]["third-state"] === true)
- from "second-state" to "third-state" (transitions["second-state"]["third-state"] === true)

The state machine may NOT transion:

- from "second-state" to "first-state" (transitions["second-state"]["first-state"] is undefined)
- away from "third-state" at all. (transitions["third-state"] is undefined)

Functional transitions

If the value defined by two states within the transitions object is a function (instead of just being "truthy"), it will be run before the transition completes.

If the function returns a FALSY value, the transition happens smoothy.

Example: Sample transitons object with transition function

const transitions = {
    "first-state":
    {
        "second-state":function(){
            return "";
        }
    }
}

If the function returns a TRUTHY value, the transition will be interrupted and a warning will be emitted containing the value returned.

Example: Sample transitons object with "interrupted" transition function

const transitions = {
    "first-state":
    {
        "second-state":function(){
            return "transition interrupted for demonstration!";
        }
    }
}

If the function throws an error, the state machine will die.

Example: Sample transitons object with transition function that kills state machine

const transitions = {
    "first-state":
    {
        "second-state":function(){
            throw new Error();
        }
    }
}

defaultState:String

The default state. This must be defined.

cleanup:Function

This optional function runs after a state machine begins to die, but before it is fully dead meaning that it's state has yet to be nullified. If defined as a non-arrow function, "this" will reference the state machine instance.

dieOnError:Boolean

This optional parameter (defalut:false) determines whether or not a state machine dies after an error.

events:Object

This set of events is passed to the constructor for the Event Emitter Class from which this class derives.

Example: Constructor

const transtions ={
    "first-state":{
        "secons-state":true
    },
    "secons-state":{
        "first-state":true
    }
}
const sm = new StateMachine(transitions, "first-state");

Instance Methods

Statemachine#getState(stateName:string)

Gets the current state.

Example: getState

sm.getState();

Also available as getter with sm.state;

Example: state (getter)

sm.state;

Statemachine#setState (stateName:string)

Attempts to set current state while invoking any transition handlers

Example: setState

await sm.setState("secons-state");

Also available as setter with sm.state.

Example: state (setter)

sm.state = "secons-state";

Statemachine#die(reason:string):

Puts state machine into a dead state where it will no longer transition. Cleanup function will run if defined.

Example: die

sm.die("reason for dying");

Statemachine#dead:boolean

Getter that returns dead status

Example: die (getter)

sm.dead;

Events

StateMachine.STATECHANGED

Emitted when state changes from one to anotuer

Emitted Specifically

- At the end of a successful call to StateMachine#.setState

Payload

- Original State
- New State
- (optional) Reason

StateMachine.STATEPENDING

Emitted when a state change begins.

Emitted Specifically

- At the beginning of a call to StateMachine#.setState

Payload

- Current State
- Desired State
- (optional) Reason

StateMachine.WARNING

Emitted when a warning is thrown but state machine does not transition into from being alive to dead.

Emitted Specifically

- A transition function is interrupted for a user defined reason (truthy return)
- An attempt to get the state of a dead state machine is made
- An attempt to set the state of a dead state machine is made

Payload

- Message indicatating what happened

StateMachine.ERROR

Emitted when a state machine throw an error Note: Stete machine will die after emitting this error, even when forced to emait

Emitted Specifically

- An attempt to transiton into a falsy state
- An attempt to transition into when a machine is alredy in pending
- An attempt to transition into a state that is ot allowed
- A transition function throws an error

Payload

- Error Message

StateMachine.DYING

Emmited when a state machine starts to die.

Emitted Specifically

- At the beginning of a call to StateMachine#.die

Payload

- (Optional) reason for dying

StateMachine.DEAD

Emmited when a state machine has died.

Emitted Specifically

- At the end of a call to StateMachine#.die

Payload

- Result of a user defined cleanup function

Development

NPM Scripts

test

runs tests

Testing

Tests can be run with node test, npm run test, or npm test

TAP

Because test output in the standard TAP format, there are a number of existing utilities that exist to format the output

Example: HTML Output

npm test | npx  tap-html --out ./tap-html.html

Example: Graphical Output

npm test | npx tap-nyan
 17  -_-_-_-_-_-_-_-_-_,------,
 0   -_-_-_-_-_-_-_-_-_|   /\_/\
 0   -_-_-_-_-_-_-_-_-^|__( ^ .^)
     -_-_-_-_-_-_-_-_-  ""  ""
 Pass!