ts-fsm-fix

🤖 Finite state machine written in typescript

❄️ ↔️ 🌊 ↔️ ♨️ Advanced control of entities' lifecycle.

npm install ts-fsm
yarn add ts-fsm

Simple usage

import StateMachine from "ts-fsm";

enum STATE {
    SOLID = "SOLID",
    LIQUID = "LIQUID",
    GAS = "GAS",
} 

enum TRANSITION {
    MELT = "MELT",
    VAPORIZE = "VAPORIZE",
    CONDENSE = "CONDENSE",
    FREEZE = "FREEZE",
}

interface IDATA {
    temperature: number;
}

const states = [{
    name: STATE.SOLID,
    data: { temperature: -100 },
}, {
    name: STATE.LIQUID,
    data: { temperature: 50 },
}, {
    name: STATE.GAS,
    data: { temperature: 200 },
}];

const transitions = [{
    name: TRANSITION.MELT,
    from: STATE.SOLID,
    to: STATE.LIQUID,
}, {
    name: TRANSITION.FREEZE,
    from: STATE.LIQUID,
    to: STATE.SOLID,
}, {
    name: TRANSITION.VAPORIZE,
    from: STATE.LIQUID,
    to: STATE.GAS,
}, {
    name: TRANSITION.CONDENSE,
    from: STATE.GAS,
    to: STATE.LIQUID,
}];

const sm = new StateMachine<STATE, TRANSITION, IDATA>(STATE.SOLID, states, transitions);

sm.state // "SOLID"
sm.data // { temperature: -100 }

sm.transitTo(STATE.LIQUID) // Promise { sm }
   .then(sm => {
       sm.state; // "LIQUID"
       sm.data; // { temperature: 50 }
   });

sm.doTransition(TRANSITION.VAPORIZE) // Promise { sm }
   .then(sm => {
       sm.state; // "GAS"
       sm.data; // { temperature: 200 }
   });

🏁🏁 Initialization

ts-fsm provide overloaded constructor and methods signature.

new StateMachine<STATE, TRANSITION, IDATA>(
    STATE.SOLID, 
    states,
    transitions
);

new StateMachine<STATE, TRANSITION, IDATA>(
    STATE.SOLID, // initial state 
    {
        before: () => {}, // beforeEachState
        states,
        after: [() => {}, () => {}], // afterEachState
    }, {
        before: () => {}, // beforeEachTransition
        transitions,
        after: [() => {}, () => {}], // afterEachTransition
    }, {
        onError: () => {};
        timeout: 1000;
    }
);

🍃🎣 Lifecycle Hooks

State machine provide several hooks for track or perform an action when a transition occurs.

As a handler, both a single function and an array of functions can be passed.

As a value, the handler takes transport, from-state, to-state. this - an instance of state machine.

transport argument - mutable object, shared and passed through each hook handler.

Transition can be canceled from any handler with explicitly return false or Promise { false }, in this case, then the subsequent handlers are not called, and state machine return to previous state.

Each handler can be limited by time with passing timeout setting into constructor.

Hook	Define	Fired
afterEachState	constructor: state: after	after any state
afterState	state: after	after specific state
beforeEachTransition	constructor: transition: before	before any transition
beforeTransition	transition: before	before specific transition
-	-	-
afterTransition	transition: after	after specific transition
afterEachTransition	constructor: transition: after	after any transition
beforeState	state: before	before specific state
beforeEachState	constructor: state: before	before any state

const increaseEntropy = ({ transport }: { transport: IObject }) => {
    transport["entropy"] = transport["entropy"] === undefined ? 0 : transport["entropy"] + 1;
};

new StateMachine<STATE, TRANSITION, IDATA>(
    STATE.SOLID, 
    {
        before: increaseEntropy, // accept single function or array of functions
        states,
        after: [ // accept single function or array of functions
            (transport, from, to) => {
                console.log(transport["entropy"]); // 0
            },
            increaseEntropy,
            (transport, from, to) => {
                console.log(transport["entropy"]); // 1
            },
        ]
    },
    transitions 
); 

Also additional aruments can be passed to transitTo and doTransition methods.

const handler = (transport, from, to, ...args) => { console.log(args); }

sm.transitTo(STATE.GAS, 1, null, "3"); // [1, null, "3"]

⏲️⏲️ Pending state

doTransition and transitTo methods set state machine into pending state.

sm.isPending; // false

sm.transitTo(STATE.GAS)
  .then(sm => {
      sm.isPending; // false
  });

sm.isPending; // true

sm.transitTo(STATE.LIQUID) // throws: StateMachineError#PENDING_STATE

🏜️🌧️ Hydration \ dehydration

Hydration\dehydration mechanism allows save\recover current state of state machine.

Getter dehydrated returns simple plain object-representation of state machine's state.

Method hydrate accept object returned by dehydrated and recover state.

const currentState = sm.hydrated;
console.log(currentState);
/* {
    state: "GAS",
    data: { temperature: 200 },
    transport: { entropy: 2 }
} */

saveToAnywhere(currentState);


// ***********
// later
const savedState = getFromAnywhere();
sm.hydrate(savedState);

🚫⚠️ Custom error handling

By default ts-fsm throw errors, but this behaviour mey be changed with onError handler function implementation.

Each time, then ts-fsm throw an error firstly will fire onError handler with error passed with first argument.

onError may throw it's custom error, otherwise ts-fsm's error will thrown.

Anyway state machine throw error.

new StateMachine<STATE, TRANSITION, IDATA>(
    STATE.SOLID, 
    states,
    transitions,
    {
        onError(error) {
            someAwesomeLogger(error);
            makeSomeAction();
            throw CustomError("Custom Error!");
        }
    }
);