Black Lives Matter. Support the Equal Justice Initiative.


Fast 1kB functional library for creating Finite State Machines

# transition

A transition is used to move from one state to another. Transitions are triggered by events, the first argument to the transition function. The second argument is the destination state.

Optionally you can add guards and reducers to transitions. Guards will be applied first; if a guard returns false the reducers will not run.

Transitions are always a child of either state or invoke types. Here's a typical transition from one state to another:

import { createMachine, state, transition } from 'robot3';

const machine = createMachine({
sleep: state(
transition('wake', 'breakfast')
breakfast: state(
transition('eat', 'work')

And similarly when used with an invoke state:

import { createMachine, invoke, state, transition } from 'robot3';
import { loadUsers } from './api.js';

const machine = createMachine({
idle: state(
transition('load', 'loading')
loading: invoke(loadUsers,
transition('done', 'show',
reduce((ctx, ev) => ({ ...ctx, users: })))
}, () => ({ users: [] }));

There can be multiple transitions for the same event, in which case the first will be chosen if its guards pass:

import { createMachine, guard, state, transition } from 'robot3';

const machine = createMachine({
shopping: state(
transition('buy', 'food',
transition('buy', 'clothes')