Ts-state-machines NPM

TypeScript State Machines

What is this? 🧐

A TypeScript library to create state machines with type safe transitions. The available state transitions for the current state will autocomplete and type check.

This is accomplished by making each state immutable, with each transition method returning the next state.

Examples 🚀

Stoplight

const Stoplight = StateMachine({
  initialState: "red",
  states: {
    red: {
      timer: "green",
    },
    green: {
      timer: "yellow",
    },
    yellow: {
      timer: "red",
    },
  },
} as const);

const stoplight = Stoplight();

// TypeScript will infer this to be 'red';
stoplight.state;

// TypeScript will infer this to be 'green';
stoplight.timer().state;

// TypeScript will infer this to be 'yellow';
stoplight.timer().timer().state;

Promiselike

const Promiselike = StateMachine({
  initialState: "pending",
  states: {
    pending: {
      start: "loading",
    },
    loading: {
      resolve: "resolved",
      reject: "rejected",
    },
    resolved: {},
    rejected: {},
  },
} as const);

const promise = Promiselike();

// TypeScript will infer this to be 'resolved';
promise.start().resolve().state;

// TypeScript will infer this to be 'rejected';
promise.start().reject().state;

Maintaining a reference to the latest state

const Stoplight = StateMachine({
  initialState: "red",
  states: {
    red: {
      timer: "green",
    },
    green: {
      timer: "yellow",
    },
    yellow: {
      timer: "red",
    },
  },
} as const);

let stoplight: StateMachineInstance<typeof Stoplight.config>;

stoplight = Stoplight();
stoplight.state; // 'red'

stoplight = stoplight.timer();
stoplight.state; // 'green'

stoplight = stoplight.timer();
stoplight.state; // 'yellow'

stoplight = stoplight.timer();
stoplight.state; // 'red'