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Version: XState v4

@xstate/vue

The @xstate/vue package contains utilities for using XState with Vue.

Quick start​

  1. Install xstate and @xstate/vue:
npm i xstate @xstate/vue

Via CDN​

<script src="https://unpkg.com/@xstate/vue/dist/xstate-vue.min.js"></script>

By using the global variable XStateVue

or

<script src="https://unpkg.com/@xstate/vue/dist/xstate-vue.fsm.min.js"></script>

By using the global variable XStateVueFSM

  1. Import the useMachine composition function:
<template>
  <button @click="send('TOGGLE')">
    {{
      state.value === 'inactive'
        ? 'Click to activate'
        : 'Active! Click to deactivate'
    }}
  </button>
</template>

<script>
import { useMachine } from '@xstate/vue';
import { createMachine } from 'xstate';

const toggleMachine = createMachine({
  id: 'toggle',
  initial: 'inactive',
  states: {
    inactive: {
      on: { TOGGLE: 'active' },
    },
    active: {
      on: { TOGGLE: 'inactive' },
    },
  },
});

export default {
  setup() {
    const { state, send } = useMachine(toggleMachine);
    return {
      state,
      send,
    };
  },
};
</script>

API​

useMachine(machine, options?)​

A Vue composition function that interprets the given machine and starts a service that runs for the lifetime of the component.

Arguments​

  • machine - An XState machine.
  • options (optional) - Interpreter options OR one of the following Machine Config options: guards, actions, activities, services, delays, immediate, context, or state.

Returns { state, send, service}:

  • state - Represents the current state of the machine as an XState State object.
  • send - A function that sends events to the running service.
  • service - The created service.

useActor(actor, getSnapshot)​

A Vue composition function that provides access to an existing actor.

Since 0.5.0

Arguments (Since 0.5.0)​

  • actor - an actor-like object that contains .send(...) and .subscribe(...) methods.
  • getSnapshot - a function that should return the latest emitted value from the actor.
    • Defaults to attempting to get the actor.state, or returning undefined if that does not exist.
import { useActor } from '@xstate/vue';

export default {
  props: ['someSpawnedActor'],
  setup(props) {
    const { state, send } = useActor(props.someSpawnedActor);
    return { state, send };
  },
};

To subscribe to changes on the an actor whilst retaining reactivity from props or another reactive variable, Vue’s computed can be used.

const { state, send } = useActor(computed(() => props.someSpawnedActor));

useInterpret(machine, options?, observer?)​

A Vue composition function that returns the service created from the machine with the options, if specified. It also sets up a subscription to the service with the observer, if provided.

Arguments (Since 0.5.0)​

  • machine - An XState machine or a function that lazily returns a machine.
  • options (optional) - Interpreter options and/or any of the following machine config options: guards, actions, services, delays, immediate, context, state.
  • observer (optional) - an observer or listener that listens to state updates:
    • an observer (e.g., { next: (state) => {/* ... */} })
    • or a listener (e.g., (state) => {/* ... */})
import { useInterpret } from '@xstate/vue';
import { someMachine } from '../path/to/someMachine';
export default {
  setup() {
    const service = useInterpret(someMachine);
    return service;
  },
};

With options + listener:

import { useInterpret } from '@xstate/vue';
import { someMachine } from '../path/to/someMachine';
export default {
  setup() {
    const service = useInterpret(
      someMachine,
      {
        actions: {
          /* ... */
        },
      },
      (state) => {
        // subscribes to state changes
        console.log(state.value);
      },
    );
    // ...
  },
};

useSelector(actor, selector, compare?, getSnapshot?)​

A Vue composition function that returns the selected value from the snapshot of an actor, such as a service. This hook will only cause a rerender if the selected value changes, as determined by the optional compare function.

Arguments (Since 0.6.0)​

  • actor - a service or an actor-like object that contains .send(...) and .subscribe(...) methods.
  • selector - a function that takes in an actor’s "current state" (snapshot) as an argument and returns the desired selected value.
  • compare (optional) - a function that determines if the current selected value is the same as the previous selected value.
  • getSnapshot (optional) - a function that should return the latest emitted value from the actor.
    • Defaults to attempting to get the actor.state, or returning undefined if that does not exist. Will automatically pull the state from services.
import { useSelector } from '@xstate/vue';

const selectCount = (state) => state.context.count;

export default {
  props: ['service'],
  setup(props) {
    const count = useSelector(props.service, selectCount);
    // ...
    return { count };
  },
};

With compare function:

import { useSelector } from '@xstate/vue';

const selectUser = (state) => state.context.user;
const compareUser = (prevUser, nextUser) => prevUser.id === nextUser.id;

export default {
  props: ['service'],
  setup(props) {
    const user = useSelector(props.service, selectUser, compareUser);
    // ...
    return { user };
  },
};

With useInterpret(...):

import { useInterpret, useSelector } from '@xstate/vue';
import { someMachine } from '../path/to/someMachine';

const selectCount = (state) => state.context.count;

export default {
  setup() {
    const service = useInterpret(someMachine);
    const count = useSelector(service, selectCount);
    // ...
    return { count, service };
  },
};

useMachine(machine) with @xstate/fsm​

A Vue composition function that interprets the given finite state machine from [@xstate/fsm] and starts a service that runs for the lifetime of the component.

This special useMachine hook is imported from @xstate/vue/lib/fsm

Arguments​

Returns an object {state, send, service}:

  • state - Represents the current state of the machine as an @xstate/fsm StateMachine.State object.
  • send - A function that sends events to the running service.
  • service - The created @xstate/fsm service.

Configuring machines​

Existing machines can be configured by passing the machine options as the 2nd argument of useMachine(machine, options).

Example: the 'fetchData' service and 'notifySuccess' action are both configurable:

<template>
  <template v-if="state.value === 'idle'">
    <button @click="send({ type: 'FETCH', query: 'something' })">
      Search for something
    </button>
  </template>

  <template v-else-if="state.value === 'loading'">
    <div>Searching...</div>
  </template>

  <template v-else-if="state.value === 'success'">
    <div>Success! {{ state.context.data }}</div>
  </template>

  <template v-else-if="state.value === 'failure'">
    <p>{{ state.context.error.message }}</p>
    <button @click="send('RETRY')">Retry</button>
  </template>
</template>

<script>
import { assign, createMachine } from 'xstate';
import { useMachine } from '@xstate/vue';

const fetchMachine = createMachine({
  id: 'fetch',
  initial: 'idle',
  context: {
    data: undefined,
    error: undefined,
  },
  states: {
    idle: {
      on: { FETCH: 'loading' },
    },
    loading: {
      invoke: {
        src: 'fetchData',
        onDone: {
          target: 'success',
          actions: assign({
            data: (_context, event) => event.data,
          }),
        },
        onError: {
          target: 'failure',
          actions: assign({
            error: (_context, event) => event.data,
          }),
        },
      },
    },
    success: {
      entry: 'notifySuccess',
      type: 'final',
    },
    failure: {
      on: {
        RETRY: 'loading',
      },
    },
  },
});

export default {
  props: {
    onResolve: {
      type: Function,
      default: () => {},
    },
  },
  setup(props) {
    const { state, send } = useMachine(fetchMachine, {
      actions: {
        notifySuccess: (ctx) => props.onResolve(ctx.data),
      },
      services: {
        fetchData: (_context, event) =>
          fetch(`some/api/${event.query}`).then((res) => res.json()),
      },
    });
    return {
      state,
      send,
    };
  },
};
</script>

Matching states​

For hierarchical and parallel machines, the state values will be objects, not strings. In this case, it’s better to use state.matches(...):

<template>
  <div>
    <loader-idle v-if="state.matches('idle')" />
    <loader-loading-user v-if-else="state.matches({ loading: 'user' })" />
    <loader-loading-friends v-if-else="state.matches({ loading: 'friends' })" />
  </div>
</template>

Persisted and rehydrated state​

You can persist and rehydrate state with useMachine(...) via options.state:

<script>
// Get the persisted state config object from somewhere, e.g. localStorage
const persistedState = JSON.parse(
  localStorage.getItem('some-persisted-state-key'),
);

export default {
  setup() {
    const { state, send } = useMachine(someMachine, {
      state: persistedState,
    });

    // state will initially be that persisted state, not the machine’s initialState
    return { state, send };
  },
};
</script>

Migration from 0.4.0​

  • For spawned actors created using invoke or spawn(...), use the useActor() hook instead of useService():

    -import { useService } from '@xstate/vue';
    +import { useActor } from '@xstate/vue';

    -const {state, send} = useService(someActor);
    +const {state, send} = useActor(someActor);