# @xstate/vue

The @xstate/vue package (opens new window) contains utilities for using XState (opens new window) with Vue (opens new window).

Vue 2 Notice:

If you're using Vue 2.x, please see the Vue recipe instead, or use the xstate-vue2 package (opens new window) if you want to use the Vue Composition API.

# 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 (opens new window) that interprets the given machine and starts a service that runs for the lifetime of the component.

Arguments

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.

# useService(service)

A Vue composition function (opens new window) that subscribes to state changes from an existing service (opens new window).

Arguments

Returns {state, send}:

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

# useActor(actor, getSnapshot)

A Vue composition function (opens new window) that subscribes to emitted changes from an existing actor (opens new window).

Since 0.5.0

Arguments

  • 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 };
  }
};

# useInterpret(machine, options?, observer?)

A Vue composition function (opens new window) 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.

Since 0.5.0

Arguments

  • machine - An XState machine (opens new window) or a function that lazily returns a machine.
  • options (optional) - Interpreter options (opens new window) 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 (opens new window) 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.

Since 0.6.0

Arguments

  • 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 (opens new window) 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.

Example (TODO)

# 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('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 (opens new window) and parallel (opens new window) machines, the state values will be objects, not strings. In this case, it's better to use state.matches(...) (opens new window):

<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);
    
Last Updated: 10/26/2021, 6:09:54 PM