Version: XState v5

@xstate/store

XState Store is a small library for simple state management in JavaScript/TypeScript applications. It is meant for updating store data using events for vanilla JavaScript/TypeScript apps, React apps, and more. It is comparable to libraries like Zustand, Redux, and Pinia. For more complex state management, you should use XState instead, or you can use XState Store with XState.

Installation

npm
pnpm
yarn

npm install @xstate/store

pnpm install @xstate/store

yarn add @xstate/store

Quick start

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

const store = createStore({
  // Initial context
  context: { count: 0, name: 'David' },
  // Transitions
  on: {
    inc: (context) => ({
      ...context,
      count: context.count + 1,
    }),
    add: (context, event: { num: number }) => ({
      ...context,
      count: context.count + event.num,
    }),
    changeName: (context, event: { newName: string }) => ({
      ...context,
      name: event.newName,
    }),
  },
});

// Get the current state (snapshot)
console.log(store.getSnapshot());
// => {
//   status: 'active',
//   context: { count: 0, name: 'David' }
// }

// Subscribe to snapshot changes
store.subscribe((snapshot) => {
  console.log(snapshot.context);
});

// Send an event (traditional way)
store.send({ type: 'inc' });
// logs { count: 1, name: 'David' }

// Send an event using the fluent trigger API
store.trigger.add({ num: 10 });
// logs { count: 11, name: 'David' }

store.trigger.changeName({ newName: 'Jenny' });
// logs { count: 11, name: 'Jenny' }

Creating a store

To create a store, pass a configuration object to the createStore(…) function with:

The initial context
An on object for transitions where the keys are event types and the values are context update functions

When updating context in transitions, you must return the complete context object with all properties:

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

const store = createStore({
  context: { count: 0, name: 'David' },
  on: {
    inc: (context) => ({
      ...context, // Preserve other context properties
      count: context.count + 1,
    }),
  },
});

Effects and Side Effects

You can enqueue effects in state transitions using the enqueue argument:

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

const store = createStore({
  context: { count: 0 },
  on: {
    incrementDelayed: (context, event, enqueue) => {
      enqueue.effect(async () => {
        await new Promise((resolve) => setTimeout(resolve, 1000));
        store.send({ type: 'increment' });
      });

      return context;
    },
    increment: (context) => ({
      ...context,
      count: context.count + 1,
    }),
  },
});

Emitting Events

You can emit events from transitions by defining them in the emits property and using enqueue.emit:

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

const store = createStore({
  context: { count: 0 },
  emits: {
    increased: (payload: { by: number }) => {
      // Optional side effects can go here
    },
  },
  on: {
    inc: (context, event: { by: number }, enqueue) => {
      enqueue.emit.increased({ by: event.by });

      return {
        ...context,
        count: context.count + event.by,
      };
    },
  },
});

// Listen for emitted events
store.on('increased', (event) => {
  console.log(`Count increased by ${event.by}`);
});

Pure transitions

You can use store.transition(state, event) to compute a tuple of the next state and any effects from a given state and event. This is useful for debugging and testing, or for having full control over the state transitions in your application.

const store = createStore({
  context: { count: 0 },
  emits: {
    incremented: (payload: { by: number }) => {},
  },
  on: {
    inc: (context, event: { by: number }, enqueue) => {
      enqueue.emit.incremented({ by: event.by });

      enqueue.effect(async () => {
        await new Promise((resolve) => setTimeout(resolve, 1000));
        store.send({ type: 'increment' });
      });

      return {
        ...context,
        count: context.count + event.by,
      };
    },
  },
});

const snapshot = store.getSnapshot();

const [nextState, effects] = store.transition(snapshot, {
  type: 'inc',
  by: 1,
});

console.log(nextState.context);
// => { count: 1 }

console.log(effects);
// => [
//   { type: 'incremented', by: 1 },
//   Function
// ]

// The store's state is unchanged
console.log(store.getSnapshot().context);
// => { count: 0 }

If you need to determine the next state from the store's initial state, you can get the initial snapshot using store.getInitialSnapshot():

const initialSnapshot = store.getInitialSnapshot();

const [nextState, effects] = store.transition(initialSnapshot, {
  type: 'inc',
  by: 1,
});

Selectors

Store selectors provide an efficient way to select and subscribe to specific parts of your store's state. With store selectors, you can:

Get the current value of a specific part of state via selector.get()
Subscribe to changes of only that specific part via selector.subscribe(observer)
Optimize performance by only notifying subscribers when the selected value actually changes via selector.subscribe(observer, equalityFn)

You can create a selector using store.select(selector):

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

const store = createStore({
  context: {
    position: { x: 0, y: 0 },
    name: 'John',
    age: 30,
  },
  on: {
    positionUpdated: (
      context,
      event: { position: { x: number; y: number } },
    ) => ({
      ...context,
      position: event.position,
    }),
  },
});

// Create a selector for the position
const position = store.select((state) => state.context.position);

// Get current value
console.log(position.get()); // { x: 0, y: 0 }

// Subscribe to changes
position.subscribe((position) => {
  console.log('Position updated:', position);
});

// When position updates, only position subscribers are notified
store.trigger.positionUpdated({ position: { x: 100, y: 200 } });
// Logs: Position updated: { x: 100, y: 200 }

Custom Equality Functions

You can provide a custom equality function as the second argument to store.select(selector, equalityFn) to control when subscribers should be notified:

const position = store.select(
  (state) => state.context.position,
  // Only notify if x coordinate changes
  (prev, next) => prev.x === next.x,
);

XState Store also provides a shallowEqual function that can be used as a default equality function:

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

const position = store.select((state) => state.context.position, shallowEqual);

Atoms

An atom is a lightweight, reactive piece of state that can be read, written to, and subscribed to. Atoms can be used standalone or combined with other atoms and stores for more complex state management.

You can:

Create an atom with createAtom(initialValue)
Read the atom's value with atom.get()
Subscribe to changes with atom.subscribe(observer)
Update the atom with atom.set(value)

Creating Atoms

Create an atom using createAtom() with an initial value:

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

// Create an atom with a primitive value
const countAtom = createAtom(0);

// Create an atom with an object
const userAtom = createAtom({ name: 'David', age: 30 });

Reading and Writing Atoms

You can read an atom's value using atom.get() and update it using atom.set():

const countAtom = createAtom(0);

// Read the current value
console.log(countAtom.get()); // 0

// Set a new value directly
countAtom.set(1); // 1

// Update value using a function
countAtom.set((prev) => prev + 1); // 2

Subscribing to Changes

Atoms support subscriptions to react to value changes:

const countAtom = createAtom(0);

// Subscribe to changes
const subscription = countAtom.subscribe((newValue) => {
  console.log('Count changed:', newValue);
});

countAtom.set(1); // Logs: "Count changed: 1"

// Unsubscribe when done
subscription.unsubscribe();

countAtom.set(2); // Does not log anything

Combined Atoms

You can create derived atoms that combine values from other atoms, stores, or selectors:

const nameAtom = createAtom('David');
const ageAtom = createAtom(30);

// Combine multiple atoms
const userAtom = createAtom((read) => ({
  name: read(nameAtom),
  age: read(ageAtom),
}));

// Combined atoms are read-only and update automatically
console.log(userAtom.get()); // { name: 'David', age: 30 }
nameAtom.set('John');
console.log(userAtom.get()); // { name: 'John', age: 30 }
ageAtom.set(31);
console.log(userAtom.get()); // { name: 'John', age: 31 }

Working with Stores and Selectors

Atoms can seamlessly integrate with XState stores and selectors:

const store = createStore({
  context: { count: 0 },
  on: {
    increment: (context) => ({ ...context, count: context.count + 1 }),
  },
});

// Create an atom from a store selector
const countSelector = store.select((state) => state.context.count);
const doubleCountAtom = createAtom((read) => 2 * read(countSelector));

console.log(doubleCountAtom.get()); // 0
store.trigger.increment();
console.log(doubleCountAtom.get()); // 2

Inspection

Just like with XState, you can use the Inspect API to inspect events sent to the store and state transitions within the store by using the .inspect method:

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

const store = createStore({
  // ...
});

store.inspect((inspectionEvent) => {
  // type: '@xstate.snapshot' or
  // type: '@xstate.event'
  console.log(inspectionEvent);
});

The .inspect(…) method returns a subscription object:

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

const sub = store.inspect((inspectionEvent) => {
  console.log(inspectionEvent);
});

// Stop listening for inspection events
sub.unsubscribe();

You can use the Stately Inspector to inspect and visualize the state of the store.

import { createBrowserInspector } from '@statelyai/inspect';
import { createStore } from '@xstate/store';

const store = createStore({
  // ...
});

const inspector = createBrowserInspector({
  // ...
});

store.inspect(inspector);

Using Immer

You can use the produce(…) function from Immer to update the context in transitions:

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

const store = createStore({
  context: { count: 0, todos: [] },
  on: {
    inc: (context, event: { by: number }) =>
      produce(context, (draft) => {
        draft.count += event.by;
      }),
    addTodo: (context, event: { todo: string }) =>
      produce(context, (draft) => {
        draft.todos.push(event.todo);
      }),
    // Not using a producer
    resetCount: (context) => ({
      ...context,
      count: 0,
    }),
  },
});

Deprecated: createStoreWithProducer(…)

In previous versions of @xstate/store, you could use the createStoreWithProducer(…) function to pass in a producer function to update the context for every transition. This will not be supported in future versions of @xstate/store. Instead, you can use the produce(…) function from Immer or similar libraries directly with createStore(…).

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

// Deprecated API
const store = createStoreWithProducer(produce, {
  context: { count: 0, todos: [] },
  on: {
    inc: (context, event: { by: number }) => {
      // No return; handled by Immer
      context.count += event.by;
    },
    addTodo: (context, event: { todo: string }) => {
      // No return; handled by Immer
      context.todos.push(event.todo);
    },
  },
});

// ...

Usage with React

If you are using React, you can use the useSelector(store, selector) hook to subscribe to the store and get the current state.

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

// Create a store
const store = createStore({
  context: { count: 0, name: 'David' },
  on: {
    inc: (context) => ({
      ...context,
      count: context.count + 1,
    }),
  },
});

// Use the `useSelector` hook to subscribe to the store
function Component(props) {
  const count = useSelector(store, (state) => state.context.count);

  // This component displays the count and has a button to increment it
  return (
    <div>
      <button onClick={() => store.trigger.inc()}>Increment</button>
    </div>
  );
}

A store can be shared with multiple components, which will all receive the same snapshot from the store instance. Stores are useful for global state management.

Local Stores with `useStore()`

The useStore() hook allows you to create local stores within React components, similar to useReducer(). This is useful when you want to manage component-specific state that doesn't need to be shared globally:

import { useStore, useSelector } from '@xstate/store/react';

function Counter({ initialCount = 0 }) {
  const store = useStore({
    context: {
      count: initialCount,
    },
    emits: {
      increased: (payload: { by: number }) => {},
    },
    on: {
      increment: (context, event: { by: number }, enqueue) => {
        enqueue.emit.increased({ by: event.by });
        return { ...context, count: context.count + event.by };
      },
    },
  });

  const count = useSelector(store, (state) => state.context.count);

  return (
    <div>
      <div>Count: {count}</div>
      <button onClick={() => store.trigger.increment({ by: 1 })}>
        Increment by 1
      </button>
      <button onClick={() => store.trigger.increment({ by: 5 })}>
        Increment by 5
      </button>
    </div>
  );
}

The store created by useStore() has all the same capabilities as a global store:

Send events using store.trigger or store.send()
Select state using useSelector()
Listen to emitted events
Use effects and side effects
Use selectors

Listening to Emitted Events

You can listen to events emitted by the local store via useEffect(…):

function Counter({
  initialCount = 0,
  onIncreased,
}: {
  initialCount?: number;
  onIncreased?: (by: number) => void;
}) {
  const store = useStore({
    // ... store config
  });

  // Listen to emitted events
  useEffect(() => {
    const subscription = store.on('increased', ({ by }) => {
      onIncreased?.(by);
    });

    return subscription.unsubscribe;
  }, [store, onIncreased]);

  // ... rest of component
}

Initializing with Props

Local stores can be initialized using component props, making them more reusable:

function Counter({ initialCount = 0, step = 1 }) {
  const store = useStore({
    context: {
      count: initialCount,
      step,
    },
    on: {
      increment: (context) => ({
        ...context,
        count: context.count + context.step,
      }),
    },
  });

  // ... rest of component
}

Props and Store State

Similar to useState and useReducer, changes to props after the initial render will not automatically update the store's state. The store's state can only be updated by sending events:

function Counter({ currentCount = 0 }) {
  const store = useStore({
    context: {
      // currentCount is only used once during initialization
      count: currentCount,
    },
    on: {
      countUpdated: (context, event: { value: number }) => ({
        ...context,
        count: event.value,
      }),
    },
  });

  // If you need to update the store when props change,
  // you'll need to send an event explicitly:
  useEffect(() => {
    store.trigger.countUpdated({ value: currentCount });
  }, [store, currentCount]);

  // ... rest of component
}

This behavior ensures that state updates are always explicit and traceable through events, maintaining a predictable data flow in your application.

Usage with Solid

Documentation coming soon!

Using XState Store with XState

You may notice that stores are very similar to actors in XState. This is very much by design. XState's actors are very powerful, but may also be too complex for simple use cases, which is why @xstate/store exists.

However, if you have existing XState code, and you enjoy the simplicity of creating store logic with @xstate/store, you can use the fromStore(context, transitions) actor logic creator to create XState-compatible store logic that can be passed to the createActor(storeLogic) function:

import { fromStore } from '@xstate/store';
import { createActor } from 'xstate';

// Instead of:
// const store = createStore( ... };
const storeLogic = fromStore({
  context: { count: 0, incremented: false /* ... */ },
  on: {
    inc: {
      count: (context, event) => context.count + 1,
      // Static values do not need to be wrapped in a function
      incremented: true,
    },
  },
});

const store = createActor(storeLogic);
store.subscribe((snapshot) => {
  console.log(snapshot);
});
store.start();

store.send({
  type: 'inc',
});

In short, you can convert createStore(…) to fromStore(…) just by changing one line of code. Note that fromStore(…) returns store logic, and not a store actor instance. Store logic is passed to createActor(storeLogic) to create a store actor instance:

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

// Instead of:
// const store = createStore({
const storeLogic = fromStore({
  context: {
    // ...
  },
  on: {
    // ...
  },
});

// Create the store (actor)
const storeActor = createActor(storeLogic);

Using fromStore(…) to create store actor logic also has the advantage of allowing you to provide input by using a context function that takes in the input and returns the initial context:

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

const storeLogic = fromStore({
  context: (initialCount: number) => ({
    count: initialCount,
  }),
  on: {
    // ...
  },
});

const actor = createActor(storeLogic, {
  input: 42,
});

Converting stores to state machines

If you have a store that you want to convert to a state machine in XState, you can convert it in a straightforward way:

Use createMachine(…) (imported from xstate) instead of createStore(…) (imported from @xstate/store) to create a state machine.
Wrap the assignments in an assign(…) action creator (imported from xstate) and move that to the actions property of the transition.
Destructure context and event from the first argument instead of them being separate arguments.

For example, here is our store before conversion:

import { createMachine } from 'xstate';

// 1. Use `createMachine(…)` instead of `createStore(…)`
const store = createStore({
  context: { count: 0, name: 'David' },
  on: {
    inc: {
      // 2. Wrap the assignments in `assign(…)`
      count: (context, event: { by: number }) => context.count + event.by,
    },
  },
});

const machine = createMachine({
  // ...
});

And here is the store as a state machine after conversion:

import { createMachine } from 'xstate';

// const store = createStore({
//   context: { count: 0, name: 'David' },
//   on: {
//     inc: {
//       count: (context, event: { by: number }) => context.count + event.by
//     }
//   }
// });

// 1. Use `createMachine(…)` instead of `createStore(…)`
const machine = createMachine({
  context: {
    count: 0,
    name: 'David',
  },
  on: {
    inc: {
      // 2. Wrap the assignments in `assign(…)`
      actions: assign({
        // 3. Destructure `context` and `event` from the first argument
        count: ({ context, event }) => context.count + event.by,
      }),
    },
  },
});

For stronger typing, use the setup(…) function to strongly type the context and events:

import { setup } from 'xstate';

const machine = setup({
  types: {
    context: {} as { count: number; name: string },
    events: {} as { type: 'inc'; by: number },
  },
}).createMachine({
  // Same as the previous example
});

Comparison

This section compares XState Store to other popular state management libraries in TypeScript. It is meant for reference purposes only, and not intended to favor one approach over the other. The examples are copied from Zustand's comparison docs.

Compare to Zustand

Zustand

import { create } from 'zustand';

type State = {
  count: number;
};

type Actions = {
  increment: (qty: number) => void;
  decrement: (qty: number) => void;
};

const useCountStore = create<State & Actions>((set) => ({
  count: 0,
  increment: (qty: number) =>
    set((state) => ({
      count: state.count + qty,
    })),
  decrement: (qty: number) =>
    set((state) => ({
      count: state.count - qty,
    })),
}));

const Component = () => {
  const count = useCountStore((state) => state.count);
  const increment = useCountStore((state) => state.increment);
  const decrement = useCountStore((state) => state.decrement);
  // ...
};

XState Store

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

const store = createStore({
  context: {
    count: 0,
  },
  on: {
    increment: (context, { qty }: { qty: number }) => ({
      ...context,
      count: context.count + qty,
    }),
    decrement: (context, { qty }: { qty: number }) => ({
      ...context,
      count: context.count - qty,
    }),
  },
});

const Component = () => {
  const count = useSelector(store, (state) => state.context.count);
  const { increment, decrement } = store.trigger;
  // ...
};

Installation​

Quick start​

Creating a store​

Effects and Side Effects​

Emitting Events​

Pure transitions​

Selectors​

Custom Equality Functions​

Atoms​

Creating Atoms​

Reading and Writing Atoms​

Subscribing to Changes​

Combined Atoms​

Working with Stores and Selectors​

Inspection​

Using Immer​

Usage with React​

Local Stores with useStore()​

Listening to Emitted Events​

Initializing with Props​

Props and Store State​

Usage with Solid​

Using XState Store with XState​

Converting stores to state machines​

Comparison​

Compare to Zustand​

Installation

Quick start

Creating a store

Effects and Side Effects

Emitting Events

Pure transitions

Selectors

Custom Equality Functions

Atoms

Creating Atoms

Reading and Writing Atoms

Subscribing to Changes

Combined Atoms

Working with Stores and Selectors

Inspection

Using Immer

Usage with React

Local Stores with `useStore()`

Listening to Emitted Events

Initializing with Props

Props and Store State

Usage with Solid

Using XState Store with XState

Converting stores to state machines

Comparison

Compare to Zustand