minimal-state-machine

Finite State machine for NodeJS with basic state transitions

Install

$ npm install @nirangad/minimal-state-machine

Usage

Initializing the state machine

In order to begin, we need to import StateMachine, StateTransition & State

import StateMachine, {
  StateTransition,
  State,
} from "@nirangad/minimal-state-machine";

State is just another string type. Set of states need to be defined before initializing the StateMachine

const states = ["new", "pending", "processing", "finalized", "invoiced", "paid"];

Then we need to define allowed transitions based on defined states. For that we use StateTransition

const transitions =  [
    new StateTransition("new", "pending"),
    new StateTransition("pending", "pending"),
    new StateTransition("new", "processing"),
    new StateTransition("pending", "processing"),
    new StateTransition("processing", "finalized"),
    new StateTransition("finalized", "invoiced"),
    new StateTransition("invoiced", "paid"),
]

Finally we can initialize the StateMachine by providing the initial state, all available states and state transitions.

const initialState = states[0];
const fsm = new StateMachine(initialState, states, transitions);

Using the state machine

StateMachine will generate functions for state transitions based on provided states. Those will be available in moveTo property.

Get current state

// Prints 'new'
console.log("State: ", fsm.state);

Transitioning to next allowed state

// Moving to 'pending' state from 'new' state
fsm.moveTo.pending();

// Prints 'pending'
console.log("State: ", fsm.state);

Invalid transitions

// Trying to move to 'finalized' state from 'pending' state
// Prints 'ERROR:  Invalid state transition: From pending to finalized'
fsm.moveTo.finalized();

Reset the state machine

fsm.reset();

// Prints 'new'
console.log("State: ", fsm.state);

Passing a callback function

// Moving to 'pending' state from 'new' state with a callback function
fsm.moveTo.pending((previousState: State, newState: State) => {
  console.log(`In Callback function: From ${previousState} to ${newState}`);
});

// Prints 'pending'
console.log("State: ", fsm.state);