xstate README

The project's README from github.com/statelyai/xstate. As one markdown file: README.md.


XState logotype
Actor-based state management & orchestration for complex app logic. → Documentation

XState is a state management and orchestration solution for JavaScript and TypeScript apps. It has zero dependencies, and is useful for frontend and backend application logic.

It uses event-driven programming, state machines, statecharts, and the actor model to handle complex logic in predictable, robust, and visual ways. XState provides a powerful and flexible way to manage application and workflow state by allowing developers to model logic as actors and state machines.

✨ Create state machines visually in Stately Studio → state.new

📖 Read the documentation

➡️ Create state machines with the Stately Editor

🖥 Download our VS Code extension

📑 Inspired by the SCXML specification

💬 Chat on the Stately Discord Community

✍️ Browse through the many XState examples

Which package should I use?

Pick based on what you need:

They work great together, but you don't need one to use the other.

Sponsors

Special thanks to the sponsors who support this open-source project:

Templates

Get started by forking one of these templates on CodeSandbox:

Template

🤖 XState Template (CodeSandbox)

Open in StackBlitz
  • XState v5
  • TypeScript
  • No framework

⚛️ XState + React Template (CodeSandbox)

Open in StackBlitz
  • React
  • XState v5
  • TypeScript

💚 XState + Vue Template (CodeSandbox)

Open in StackBlitz
  • Vue
  • XState v5
  • TypeScript

🧡 XState + Svelte Template (CodeSandbox)

Open in StackBlitz

Super quick start

npm install xstate

import { createMachine, createActor, assign } from 'xstate';

// State machine
const toggleMachine = createMachine({
  id: 'toggle',
  initial: 'inactive',
  context: {
    count: 0
  },
  states: {
    inactive: {
      on: {
        TOGGLE: { target: 'active' }
      }
    },
    active: {
      entry: assign({ count: ({ context }) => context.count + 1 }),
      on: {
        TOGGLE: { target: 'inactive' }
      }
    }
  }
});

// Actor (instance of the machine logic, like a store)
const toggleActor = createActor(toggleMachine);
toggleActor.subscribe((state) => console.log(state.value, state.context));
toggleActor.start();
// => logs 'inactive', { count: 0 }

toggleActor.send({ type: 'TOGGLE' });
// => logs 'active', { count: 1 }

toggleActor.send({ type: 'TOGGLE' });
// => logs 'inactive', { count: 1 }

@xstate/store: simple state management

Not every app needs all the features of state machines and statecharts. @xstate/store is a separate, extremely small event-based store with first-class TypeScript inference; similar to Redux or Zustand, but with less boilerplate.

Use it on its own, or graduate to full XState machines when your logic gets more complex.

npm install @xstate/store

import { createStore } from '@xstate/store';

const donutStore = createStore({
  context: {
    donuts: 0,
    favoriteFlavor: 'chocolate'
  },
  on: {
    addDonut: (context) => ({ ...context, donuts: context.donuts + 1 }),
    changeFlavor: (context, event: { flavor: string }) => ({
      ...context,
      favoriteFlavor: event.flavor
    }),
    eatAllDonuts: (context) => ({ ...context, donuts: 0 })
  }
});

donutStore.subscribe((snapshot) => {
  console.log(snapshot.context);
});

donutStore.send({ type: 'addDonut' });
// => { donuts: 1, favoriteFlavor: 'chocolate' }

donutStore.send({ type: 'changeFlavor', flavor: 'strawberry' });
// => { donuts: 1, favoriteFlavor: 'strawberry' }

📖 See the @xstate/store README for React/Solid bindings, selectors, and more.

Stately Studio

XState Viz

state.new

Why?

Statecharts are a formalism for modeling stateful, reactive systems. This is useful for declaratively describing the behavior of your application, from the individual components to the overall application logic.

Read 📽 the slides (🎥 video) or check out these resources for learning about the importance of finite state machines and statecharts in user interfaces:

Packages

Package Description
🤖 xstate Core finite state machine and statecharts library + interpreter, including graph traversal and model-based testing utilities
🏪 @xstate/store Simple event-based state management (<1kb) — standalone, works with or without xstate
⚛️ @xstate/react React hooks and utilities for using XState in React applications
💚 @xstate/vue Vue composition functions and utilities for using XState in Vue applications
🎷 @xstate/svelte Svelte utilities for using XState in Svelte applications
🥏 @xstate/solid Solid hooks and utilities for using XState in Solid applications
🔍 @statelyai/inspect Inspection utilities for XState

Finite State Machines

CodeStatechart
 
import { createMachine, createActor } from 'xstate';

const lightMachine = createMachine({
  id: 'light',
  initial: 'green',
  states: {
    green: {
      on: {
        TIMER: 'yellow'
      }
    },
    yellow: {
      on: {
        TIMER: 'red'
      }
    },
    red: {
      on: {
        TIMER: 'green'
      }
    }
  }
});

const actor = createActor(lightMachine);

actor.subscribe((state) => {
  console.log(state.value);
});

actor.start();
// logs 'green'

actor.send({ type: 'TIMER' });
// logs 'yellow'
Finite states
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Hierarchical (Nested) State Machines

CodeStatechart
 
import { createMachine, createActor } from 'xstate';

const pedestrianStates = {
  initial: 'walk',
  states: {
    walk: {
      on: {
        PED_TIMER: 'wait'
      }
    },
    wait: {
      on: {
        PED_TIMER: 'stop'
      }
    },
    stop: {}
  }
};

const lightMachine = createMachine({
  id: 'light',
  initial: 'green',
  states: {
    green: {
      on: {
        TIMER: 'yellow'
      }
    },
    yellow: {
      on: {
        TIMER: 'red'
      }
    },
    red: {
      on: {
        TIMER: 'green'
      },
      ...pedestrianStates
    }
  }
});

const actor = createActor(lightMachine);

actor.subscribe((state) => {
  console.log(state.value);
});

actor.start();
// logs 'green'

actor.send({ type: 'TIMER' });
// logs 'yellow'

actor.send({ type: 'TIMER' });
// logs { red: 'walk' }

actor.send({ type: 'PED_TIMER' });
// logs { red: 'wait' }
Hierarchical states
Open in Stately Studio

Parallel State Machines

CodeStatechart
 
import { createMachine, createActor } from 'xstate';

const wordMachine = createMachine({
  id: 'word',
  type: 'parallel',
  states: {
    bold: {
      initial: 'off',
      states: {
        on: {
          on: { TOGGLE_BOLD: 'off' }
        },
        off: {
          on: { TOGGLE_BOLD: 'on' }
        }
      }
    },
    underline: {
      initial: 'off',
      states: {
        on: {
          on: { TOGGLE_UNDERLINE: 'off' }
        },
        off: {
          on: { TOGGLE_UNDERLINE: 'on' }
        }
      }
    },
    italics: {
      initial: 'off',
      states: {
        on: {
          on: { TOGGLE_ITALICS: 'off' }
        },
        off: {
          on: { TOGGLE_ITALICS: 'on' }
        }
      }
    },
    list: {
      initial: 'none',
      states: {
        none: {
          on: {
            BULLETS: 'bullets',
            NUMBERS: 'numbers'
          }
        },
        bullets: {
          on: {
            NONE: 'none',
            NUMBERS: 'numbers'
          }
        },
        numbers: {
          on: {
            BULLETS: 'bullets',
            NONE: 'none'
          }
        }
      }
    }
  }
});

const actor = createActor(wordMachine);

actor.subscribe((state) => {
  console.log(state.value);
});

actor.start();
// logs {
//   bold: 'off',
//   italics: 'off',
//   underline: 'off',
//   list: 'none'
// }

actor.send({ type: 'TOGGLE_BOLD' });
// logs {
//   bold: 'on',
//   italics: 'off',
//   underline: 'off',
//   list: 'none'
// }

actor.send({ type: 'TOGGLE_ITALICS' });
// logs {
//   bold: 'on',
//   italics: 'on',
//   underline: 'off',
//   list: 'none'
// }
Parallel states
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History States

CodeStatechart
 
import { createMachine, createActor } from 'xstate';

const paymentMachine = createMachine({
  id: 'payment',
  initial: 'method',
  states: {
    method: {
      initial: 'cash',
      states: {
        cash: {
          on: {
            SWITCH_CHECK: 'check'
          }
        },
        check: {
          on: {
            SWITCH_CASH: 'cash'
          }
        },
        hist: { type: 'history' }
      },
      on: { NEXT: 'review' }
    },
    review: {
      on: { PREVIOUS: 'method.hist' }
    }
  }
});

const actor = createActor(paymentMachine);

actor.subscribe((state) => {
  console.log(state.value);
});

actor.start();
// logs {
//   value: { method: 'cash' },
// }

actor.send({ type: 'SWITCH_CHECK' });
// logs {
//   value: { method: 'check' },
// }

actor.send({ type: 'NEXT' });
// logs {
//   value: 'review',
// }

actor.send({ type: 'PREVIOUS' });
// logs {
//   value: { method: 'check' },
// }
History state
Open in Stately Studio

SemVer Policy

We understand the importance of the public contract and do not intend to release any breaking changes to the runtime API in a minor or patch release. We consider this with any changes we make to the XState libraries and aim to minimize their effects on existing users.

Breaking changes

XState executes much of the user logic itself. Therefore, almost any change to its behavior might be considered a breaking change. We recognize this as a potential problem but believe that treating every change as a breaking change is not practical. We do our best to implement new features thoughtfully to enable our users to implement their logic in a better, safer way.

Any change could affect how existing XState machines behave if those machines are using particular configurations. We do not introduce behavior changes on a whim and aim to avoid making changes that affect most existing machines. But we reserve the right to make some behavior changes in minor releases. Our best judgment of the situation will always dictate such changes. Please always read our release notes before deciding to upgrade.

TypeScript changes

We also reserve a similar right to adjust declared TypeScript definitions or drop support for older versions of TypeScript in a minor release. The TypeScript language itself evolves quickly and often introduces breaking changes in its minor releases. Our team is also continuously learning how to leverage TypeScript more effectively - and the types improve as a result.

For these reasons, it is impractical for our team to be bound by decisions taken when an older version of TypeScript was its latest version or when we didn’t know how to declare our types in a better way. We won’t introduce declaration changes often - but we are more likely to do so than with runtime changes.

Packages

Most of the packages in the XState family declare a peer dependency on XState itself. We’ll be cautious about maintaining compatibility with already-released packages when releasing a new version of XState, but each release of packages depending on XState will always adjust the declared peer dependency range to include the latest version of XState. For example, you should always be able to update xstate without @xstate/react. But when you update @xstate/react, we highly recommend updating xstate too.

xstate (statelyai/xstate)

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30.3K ·GitHub
Xstate
What is this?XState is a state management and orchestration solution for JavaScript and TypeScript apps. It models complex application logic as state machines, statecharts, and actors, so behavior stays predictable, robust, and visual.
Is this a library I add to my project, or a separate tool?A family of npm libraries: the core xstate package is a finite state machine and statechart library with an interpreter, plus companion packages like @xstate/store and framework bindings such as @xstate/react.
How do I get it running?Install the xstate package from npm, or fork one of the ready-made CodeSandbox templates — plain TypeScript, React, Vue, or Svelte — to try it in the browser right away.
Does it work with React and Vue?Yes — the core library is framework-agnostic with zero dependencies and runs on both frontend and backend, with official integrations for React, Vue, and Svelte if you want them.
Anything to watch out for when upgrading to newer versions?Since XState executes much of your app's logic itself, minor releases may include behavior changes, and TypeScript definitions may be adjusted in minors too — always read the release notes before upgrading.
What is @xstate/store and when would I pick it over full XState?It's a separate, extremely small event-based store with first-class TypeScript inference — similar to Redux or Zustand but with less boilerplate. Start there for simple state management and graduate to full state machines when your logic gets more complex.
What is Stately Studio?A visual editor for creating, editing, and collaborating on state machines. It exports to XState v5, autogenerates test paths and documentation, can deploy to Stately Sky, and includes AI-assisted machine generation.
Why model app logic as statecharts instead of plain state management?Statecharts are a formalism for modeling stateful, reactive systems. They describe application behavior declaratively — from individual components up to overall app logic — which keeps complex flows predictable and easy to visualize.
Can I edit my machines visually inside my editor?Yes — there's a VS Code extension for XState, and for full visual editing with collaboration and autogeneration you can open machines in Stately Studio.
What are similar projects?Recoil, jotai, formily, shaders, akka-core, xyflow, mitosis, blobatar
Which topics is it in?actor-model, state, state-machine, background-jobs, interpreter, reactive, event-driven, svelte, state-management, workflow, orchestration, vue
Creator
statelyai
Size
273 MB
Stars
30.3K
Updated
CommitOct 17Release[email protected]Oct 17
Age
11y
Commits · 90 Days