X-Robot FSM

X-Robot FSM: A lightweight, developer-friendly finite state machine library for JavaScript and TypeScript.

Why X-Robot?

• Entry pulses — Async state management without boilerplate
• Frozen state by default — No manual cloning required
• Native async guards — No workarounds needed
• Small bundle — 16.55KB core, 79.93KB with documentate + validate
• Fast — 1.1-15.4x faster than XState in benchmarks
• TypeScript — Includes TypeScript types for machine definitions and generated code
• Living visual docs — documentate() separates visual outputs by concept:
  • Mermaid: Markdown-friendly source diagrams and previews
  • PlantUML: richer source diagrams and preferred visual styling
  • SVG formats: explicit svg-* exports for sharing, embedding, and vector assets
  • PNG formats: explicit png-* exports for raster docs, tickets, and slides
• Redux DevTools integration — Inspect wrapped machine operations with x-robot/devtools

Quick Start

import {
  machine,
  state,
  initial,
  init,
  context,
  transition,
  invoke,
  entry
} from "x-robot";

// Define a fetch machine with async handling
async function fetchData(ctx) {
  const res = await fetch("/api/data");
  ctx.data = await res.json();
}

const fetchMachine = machine(
  "Fetch",
  init(initial("idle"), context({ data: null, error: null })),
  state("idle", transition("fetch", "loading")),
  state("loading", entry(fetchData, "success", "error")),
  state("success", transition("reset", "idle")),
  state("error", transition("reset", "idle"))
);

await invoke(fetchMachine, "fetch");
console.log(fetchMachine.current); // "success" or "error"
console.log(fetchMachine.context.data); // { ... }

Installation

npm install x-robot
# or
bun add x-robot

Framework Adapters

Official framework adapters:

• @x-robot/react - React hook: useMachine(machine, options?)
• @x-robot/vue - Vue composable: useMachine(machine, options?)
• v1 contract: framework updates are guaranteed only for the wrapper methods returned by the adapter (start, invoke, invokeAfter)
• Important caveat: direct external invoke(machine, ...) calls are not tracked in v1

Adapter docs:

• Framework guide: docs/guides/framework-adapters.md
• React: packages/react/README.md
• Vue: packages/vue/README.md

Key Features

• Nested and parallel states
• Guards (synchronous and asynchronous)
• Immediate transitions
• Entry and exit pulses
• Context management with frozen state
• Delayed transitions with invokeAfter()
• History tracking
• Redux DevTools integration via x-robot/devtools
• Machine validation with validate()
• Code generation (TypeScript, ESM, CJS)
• Diagram generation:
  • Mermaid: Markdown-friendly state diagrams, sequence diagrams, and focused structural maps
  • PlantUML: richer source diagrams for state, sequence, and focused structural views
  • SVG formats: explicit svg-* exports for sharing, embedding, and vector assets
  • PNG formats: explicit png-* exports for raster images in docs, tickets, and slides
• SCXML import/export

Redux DevTools

Use x-robot/devtools to connect a machine to the Redux DevTools Extension during development.

if (import.meta.env.DEV) {
  const { connectXRobot } = await import("x-robot/devtools");
  const connection = connectXRobot(fetchMachine, {
    name: "Fetch"
  });

  await connection.start();
  await connection.invoke("fetch");
  connection.disconnect();
}

See docs/guides/devtools.md for setup, supported monitor actions, production exclusion, and cleanup patterns.

API Overview

Function	Purpose
machine()	Create a state machine
state()	Define a state
transition()	Define state transitions
invoke()	Trigger a transition
entry()	Entry pulse - runs when entering a state
exit()	Exit pulse - runs when leaving a state
guard()	Conditional transitions
invokeAfter()	Delayed transitions
connectXRobot()	Connect Redux DevTools via x-robot/devtools
documentate()	Generate code, serialization, Mermaid diagrams, PlantUML diagrams, explicit svg-* image exports, and explicit png-* image exports via x-robot/documentate
validate()	Validate machine structure via x-robot/validate

Documentation

docs/guides/getting-started.md · docs/guides/framework-adapters.md · docs/guides/visualization.md · docs/guides/serialization.md · docs/guides/devtools.md · docs/guides/publishing-adapters.md · packages/react/README.md · packages/vue/README.md · docs/concepts/ · docs/api/ · docs/recipes/ · docs/performance.md

License

Apache-2.0