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Fiume 🏞️

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Fiume is a zero-dependency, simple, and flexible state machine library written in TypeScript. It supports Deterministic and partially Non-Deterministic state machines. It is compatible with all JavaScript runtimes and is designed to manage the flow of a system through various states. This library provides a lightweight and intuitive way to define states, transitions, and hooks for state entry, exit, and transition events.

Unlike other libraries, Fiume does not require hardcoding state transitions. Instead, you can write the transition logic inside the transitionTo function.

Docs

You can find documentation and examples at fiume.dev.

Installation

npm install fiume

Usage

import { StateMachine, State } from "fiume";

// Define a simple ON-OFF machine
const states: Array<State> = [
  {
    id: "OFF",
    initial: true,
    transitionGuard: ({ event }) => event === 'button clicked',
    transitionTo: () => "ON",
  },
  {
    id: "ON",
    transitionGuard: ({ event }) => event === 'button clicked',
    transitionTo: () => "OFF",
  },
];

// Create a state machine instance
const machine = StateMachine.from(states);

// Start the state machine
await machine.start();
console.log(machine.currentStateId); // OFF

// Trigger a transition by sending an event
await machine.send('button clicked');
console.log(machine.currentStateId); // ON

// Trigger another transition
await machine.send('button clicked');
console.log(machine.currentStateId); // OFF

// Trigger another transition
await machine.send('wrong event'); // wrong event wont trigger the transition
console.log(machine.currentStateId); // OFF

With autoTransition set to true, the machine does not wait for the send method to trigger the transition to the next state:

import { StateMachine, State } from "fiume";

const states: Array<State> = [
  {
    id: "OFF",
    initial: true,
    autoTransition: true,
    transitionTo: () => "ON",
  },
  {
    id: "ON",
    final: true,
  },
];

const machine = StateMachine.from(states);
await machine.start();
console.log(machine.currentStateId); // ON

You can define custom hooks onEntry, onExit and onFinal:

const states: Array<State> = [
  {
    id: "OFF",
    initial: true,
    transitionTo: async ({ context, event, sharedData }) => "ON",
    onEntry: async ({ context, event, sharedData }) => console.log(event.name, event.value),
    onExit: async ({ context, event, sharedData }) => console.log(event.name, event.value),
  },
  {
    id: "ON",
    final: true,
    transitionTo: ({ context, event, sharedData }) => "OFF",
    onEntry: async ({ context, event, sharedData }) => console.log(event.name, event.value),
    onExit: ({ context, event, sharedData }) => console.log(event.name, event.value),
    onFinal: ({ context, event, sharedData }) => console.log(event.name, event.value),
  },
];

type MyContext = { foo: string, bar: string }
type MyEvent = { name: string, value: number }

const machine = StateMachine.from<MyContext, MyEvent>(
  states,
  { context: { foo: 'foo', bar: 'bar' }}
);

// Start the state machine
await machine.start();

await machine.send({ name: 'foo', value: 1 });
machine.currentStateId; // ON
await machine.send({ name: 'foo', value: 2 });
machine.currentStateId; // OFF

You can also subscribe to state transitions:

const states: Array<State> = [
  {
    id: "ONE",
    initial: true,
    transitionTo: () => "TWO",
  },
  {
    id: "TWO",
    transitionTo: () => "THREE",
  },
  { id: "THREE", final: true },
];

const machine = StateMachine.from(states);
await machine.start();

// Subscribe to state transitions
const subId = machine.subscribe(
  ({ context, currentStateId }) => console.log(currentStateId)
); // ONE, TWO
console.log(machine.currentStateId); // ONE
await machine.send();
console.log(machine.currentStateId); // TWO

// Unsubscribe the previous subscription
machine.unsubscribe(subId);

await machine.send();
console.log(machine.currentStateId); // THREE

API

StateMachine

Constructor

StateMachine.from: A static function that returns a new instance of the state machine. It takes the following parameters:
- states: An array of State objects representing the states of the state machine.
- options (optional): Configuration options for the state machine:
  - id (string): The id of the machine,
  - context: User-defined object.
  Don't add in context objects that cannot be copied, like database connections, sockets, emitter, request, etc. Instead use sharedData!
  - sharedData: User-defined object.
  Use sharedData to store database connection, sockets, request/response, etc.

Example:

import { StateMachine } from "fiume";
const machine = StateMachine.from(states, options);

StateMachine.fromSnapshot: A static function that returns a new instance of the state machine from an existing snapshot. It takes the following parameters:
- snapshot: The snapshot object produced by machine.createSnapshot().
- states: An array of State objects representing the states of the state machine.
- sharedData (optional): User-defined object.

Example:

import { StateMachine } from "fiume";
const machine = StateMachine.from(states, options);
await machine.start();
const snapshot = machine.createSnapshot();
const refromSnapshot = StateMachine.fromSnapshot(snapshot, states);

Public Methods

start (async): Initiates the state machine and triggers the execution of the initial state.
send (async): Send events to states that are not autoTransition. If current state has autoTransition: false, calling the send function is required to move to next state. If the machine is in a final state and isFinished set to true, using send will reject.
createSnapshot: Returns a snapshot of the current machine with the following properties:
- snapshotId (string): Id of the current snapshot.
- machineId: (string): Id of the machine.
- stateId: (string): Id of the current state when snapshot is taken.
- context: (TContext): User defined context
sharedData will not be snapshotted!
subscribe: You can register a callback that will be invoked on every state transition between the onEntry and onExit hooks. The callback returns the subscriptionId and receives context, event, sharedData, and currentStateId.
unsubscribe: Remove the subscription with the given subscriptionId.

Public properties

id string: The id of the machine, if not supplied in the constructor, will be a randomUUID.
currentStateId string: The id of current state of the machine.
isFinished boolean: True if the machine has finished in a final state.
context: User defined context.
sharedData (TSharedData): User defined data shared with the state machine.

Do not add in context, objects that cannot be copied, like database connections, EventEmitter, Request, Socket, use sharedData instead!

State

Represents a state in the state machine.

id: (required) Unique identifier for the state.
transitionTo (optional): Function or AsyncFunction that defines the transition logic to move to another state, must return the id of the next state.
autoTransition (optional): Boolean, if true the machine will transition to the next state without waiting for an event. If set to true is not possibile to use transitionGuard.
onEntry (optional): Hook called when entering the state.
onExit (optional): Hook called when exiting the state.
onFinal (optional): Hook called when execution has ended in final state.
initial (optional): Boolean indicating whether the state is the initial state, there can only be one initial state.
final (optional): Boolean indicating whether the state is a final state.
transitionGuard (optional): Function or AsyncFunction takes as input a user event and defines whether or not transition to the next state