Use @avaragado/xstateful with React, accessing states and activities from multiple statecharts anywhere in your app

See https://codesandbox.io/s/6lyq0yl4rz for a full example, simulating UK-style traffic lights and a pedestrian crossing (the source is in the examples/pelican directory).

• Provider/consumer model Call a function to create React components from an XStateful instance. Add the provider near the app root, and use consumers lower down the tree to access machine state and extended state.
• Specialised consumer components Use declarative components that render based on machine activities, machine state, or any function.
• Familiar props Consumer components accept component prop, render prop, function-as-child, or child nodes, very similar to react-router.
• Lifecycle helper A special component lets you "set up" and "tear down" a machine on mount/unmount if you need to.

• React 16.3+ (uses React's new "context" functionality)

The @avaragado/xstateful package is a self-contained interpreter for statecharts, wrapping xstate and adding support for reducers, extended state, and time-based events. xstateful itself doesn't render anything.

xstateful-react works with xstateful to let you render React components based on your statechart, and trigger state transitions.

Terms are as used in xstateful, plus common terms in React development such as render props, function-as-child, and the provider/consumer pattern of React Context.

$ yarn add xstate @avaragado/xstateful @avaragado/xstateful-react
$ # or
$ npm install xstate @avaragado/xstateful @avaragado/xstateful-react

In summary:

1. Use xstateful to create an XStateful instance (either instantiating XStateful directly, or by calling createStatefulMachine).
2. Call the xstateful-react function createReactMachine, passing your XStateful instance. This function returns a number of components (a provider and several consumers).
3. Add the provider component somewhere near the root of your app.
4. Add the consumer components as necessary as direct or indirect descendants of the provider.
5. Add the control component if needed to set up/tear down your machine at the right places in your app.

Use one module to export an XStateful instance and the React components generated by xstateful-react. You can test the XStateful instance in isolation, without worrying about particular rendering environments.

// my-react-machine.js

import { Machine } from 'xstate';
import { createStatefulMachine } from '@avaragado/xstateful';
import { createReactMachine } from '@avaragado/xstateful-react';

const machine = Machine({
    // xstate machine configuration
});
const reducer = ... // if needed
const extstate = ... // if needed

export const xsf = createStatefulMachine({ machine, reducer, extstate });

export default createReactMachine(xsf);

Near the root of the render tree, add the provider component (it accepts no props). It doesn't have to look exactly like this: as long as the provider is an ancestor of all the consumers, it's fine.

The object returned by createReactMachine is a general-purpose consumer component, described in full below. It has properties for the other, more specialised consumers, plus a property for the provider, and one for the control component. This structure is intended to "read well" to aid understanding when inspecting a component tree.

// my-root.jsx

import React from 'react';
import ReactDOM from 'react-dom';

import MyApp from './my-app';
import MyReactMachine from './my-react-machine';

ReactDOM.render(
    <MyReactMachine.Provider>
        <MyApp />
    </MyReactMachine.Provider>,
    document.getElementById('root'),
);

Lower down the render tree, render the consumer components. They all accept component, render and children props that work almost identically to react-router. They also nest, with predictable results. Full descriptions of each component are below – this example component just shows a few options.

// my-random-component.jsx

import React from 'react';

import MyReactMachine from './my-react-machine';

const MyRandomComponent = () => (
    <div>
        <p>Blah...</p>

        {/* the main component renders according to a function of state and extended state */}
        <MyReactMachine
            cond={({ state, extstate }) =>
                state.value === 'boink' && extstate.foo === 'bar'
            }
        >
            <p>Rendered if cond evaluates to true</p>
        </MyReactMachine>

        {/* the .Activity component renders according to current machine activities */}
        <MyReactMachine.Activity is="pending">
            Loading...
        </MyReactMachine.Activity>
        <MyReactMachine.Activity is={['error', 'timeout']}>
            Something went wrong
        </MyReactMachine.Activity>

        {/* the .State component renders according to current machine state value */}
        <MyReactMachine.State is="a.b.c"> ... </MyReactMachine.State>
        <MyReactMachine.State is={['a.b.c', 'a.b.d']}>...</MyReactMachine.State>
    </div>
);

export default MyRandomComponent;

Some XStateful machines may need special "set up" and "tear down" behaviour. For example, consider a machine that sends an event on a periodic timer when it's in a particular state. This machine keeps sending that event even when it's not mounted in the component tree, for as long as it remains in this state. (This is because the XStateful instance is decoupled from React.)

This might be what's needed for an app: every app is different. Some apps might instead want to "power down" a machine when it's not mounted. Use the Control component to do this.

// my-other-component.jsx

import React from 'react';

import MyReactMachine from './my-react-machine';

const MyOtherComponent = () => (
    <MyReactMachine.Control
        onDidMount={({ transition }) => transition('POWER_ON');}
        onWillUnmount={({ transition }) => transition('POWER_OFF');}
    >
        ...other components, including consumer components from MyReactMachine
    </MyReactMachine.Control
);

export default MyOtherComponent;

import { createReactMachine } from '@avaragado/xstateful-react';

Returns a general-purpose React consumer component (let's call it Machine) tied to the input XStateful instance. Machine holds other components, as properties Activity, State, Provider and Control.

This is a React component that gives access to values from Machine.Provider rendered higher in the tree. Use these values, through props, to determine whether to render other components.

Machine props:

• cond?: boolean | (({ state, extstate }) => boolean)
• component?: React.ComponentType<{ state, extstate, init, transition, setExtState }>
• render?: ({ state, extstate, init, transition, setExtState }) => React.Node
• children?: React.Node | ({ state, extstate, init, transition, setExtState, match }) => React.Node

The arguments/props state, extstate, init, transition and setExtState correspond to the XStateful instance: state contains machine state, extstate contains extended state, init is a function to initialise or reset the machine, transition is a function to send an event to the machine, and setExtState is a function to update extended state.

If more than one of component, render and children are specified, component takes precedence over render, and render takes precedence over children.

The boolean value from cond (which defaults to true if cond is omitted), combined with component/render/children, define what's rendered.

• With component:
  • When cond is true, creates a React element from that component, passing the props state, extstate, init, transition and setExtState, and renders that.
  • When cond is false, renders null.
• With render:
  • When cond is true, calls the render prop function passing a single object arg { state, extstate, init, transition, setExtState } and renders the result.
  • When cond is false, renders null.
• With children nodes (not function-as-child form):
  • When cond is true, renders the children.
  • When cond is false, renders null.
• With children function:
  • Calls the function, passing a single object arg { state, extstate, init, transition, setExtState, match }, where match is the boolean result of cond, and renders the result.

Examples:

<Machine cond={other_value_in_scope}>
    <p>Rendered only if cond value is true</p>
</Machine>

<Machine cond={mc => mc.extstate.foo === 123}>
    <p>Rendered only if cond evaluates to true</p>
</Machine>

<Machine cond={mc => mc.extstate.foo === 123}>
    {({ match }) => (
        <p>Rendered always, cond result is in match</p>
    )}
</Machine>

<Machine
    cond={mc => mc.state.actions.length === 0}
    component={RenderedOnlyIfCondTrue}
/>

<Machine
    cond={mc => otherfunction(mc, othervalue)}
    render={
        ({ state }) => (<p>rendered only if cond true</p>)
    }
/>

<Machine>
    {({ state, extstate, init, transition, setExtState }) => {
        // render something!
    }}
</Machine>

This is a React component that sprinkles some sugar over Machine, focusing on the activities emitted by the statechart.

Machine.Activity props:

• is?: string | Array<string> | (({ [activity: string]: boolean }) => boolean)
• not?: string | Array<string> | (({ [activity: string]: boolean }) => boolean)
• component?: React.ComponentType<{ state, extstate, init, transition, setExtState }>
• render?: ({ state, extstate, init, transition, setExtState }) => React.Node
• children?: React.Node | ({ state, extstate, init, transition, setExtState, match }) => React.Node

The is and not props check against the statechart's current activities.

• is="foo" matches if the string is a current activity.
• not="foo" matches if the string is not a current activity.
• is={['foo', 'bar']} matches if any of the array members is a current activity.
• not={['foo', 'bar']} matches if none of the array members is a current activity.
• is={myFunction} matches if the function, when passed an object { [activity: string]: boolean } describing the statechart's current activities, returns true.
• not={myFunction} matches if the function, when passed an object { [activity: string]: boolean } describing the statechart's current activities, returns false.

The boolean result of the match feeds in to the component, render and children props as described above for Machine.

Examples:

<Machine.Activity is="buzzing">
    <p>Power is on!</p>
</Machine.Activity>

<Machine.Activity
    not={['fizzing', 'buzzing']}
    component={MostlyHarmless}
/>

<Machine.Activity is="open">
    {({ match }) => (
        <p>match is true if activity "open" is current, false otherwise</p>
    )}
</Machine.Activity>

This is a React component that sprinkles some sugar over Machine, focusing on the current state(s) of the statechart.

Machine.State props:

• is?: string | Array<string> | (({ [activity: string]: boolean }) => boolean)
• not?: string | Array<string> | (({ [activity: string]: boolean }) => boolean)
• component?: React.ComponentType<{ state, extstate, init, transition, setExtState }>
• render?: ({ state, extstate, init, transition, setExtState }) => React.Node
• children?: React.Node | ({ state, extstate, init, transition, setExtState, match }) => React.Node

The is and not props check against the statechart's current states.

• is="foo" matches if the string is a current state.
• not="foo" matches if the string is not a current state.
• is={['foo', 'bar']} matches if any of the array members is a current state.
• not={['foo', 'bar']} matches if none of the array members is a current state.
• is={myFunction} matches if the function, when passed an xstate state value, returns true.
• not={myFunction} matches if the function, when passed an xstate state value, returns false.

The state check uses the xstate utility matchesState, and supports parallel and nested states. For example, if the statechart is currently in states a.b.c and a.b.d, then a check is="a.b" will match.

The boolean result of the match feeds in to the component, render and children props as described above for Machine.

Examples:

<Machine.State is="idle">
    <p>Waiting for input</p>
</Machine.State>

<Machine.State
    not={['a.b', 'a.c']}
    render={({ exstate }) => (
        <Something val={extstate.foo} />
    )}
/>

<Machine.State is={someComplexFunctionOfStateValue}>
    {({ match }) => (
        <p>match is boolean result of function</p>
    )}
</Machine.State>

This React component holds the link to the XStateful instance for the statechart. It provides current machine state and extended state values, and functions to send events, to all related consumer components (Machine, Machine.Activity, Machine.State) rendered as descendants in the render tree.

No props.

This React component includes two props that map to React lifecycle methods. Use these props to initialise and/or send events to the statechart when the React component mounts and/or unmounts. Not all apps need to use it.

Machine.Control props:

• onDidMount?: ({ state, extstate, init, transition, setExtState }) => void
• onWillUnmount?: ({ state, extstate, init, transition, setExtState }) => void
• children: React.Node

The arguments/props state, extstate, init, transition and setExtState correspond to the XStateful instance: state contains machine state, extstate contains extended state, init is a function to initialise or reset the machine, transition is a function to send an event to the machine, and setExtState is a function to update extended state.

The component always renders its children.

The component calls the onDidMount function in its own componentDidMount lifecycle method, and onWillUnmount in its own componentWillUnmount lifecycle method.

Examples:

<Machine.Control onDidMount={({ init }) => init()}>
    ...
</Machine.Control>

<Machine.Control
    onDidMount={({ transition }) => transition('POWER_ON')}
    onWillUnmount={({ transition }) => transition('POWER_OFF')}
>
    ...
</Machine.Control>

• xstate, by David Khourshid
• react-finite-machine, by Derek Duncan
• react-automata, by Michele Bertoli

David Smith (@avaragado)

Bug reports, feature requests and PRs are gratefully received. Add an issue or submit a PR.

Please note that this project is released with a Contributor Code of Conduct. By participating in this project you agree to abide by its terms.

Thanks goes to these wonderful people (emoji key):

David Smith 📖 💻 ⚠️	ShMcK 📖

This project follows the all-contributors specification. Contributions of any kind welcome!

The package.json file contains all the usual scripts for linting, testing, building and releasing.

Buzzwords: prettier, eslint, flow, flow-typed, babel, jest, rollup, react.

When merging to master Squash and Merge.

In the commit message, follow conventional-changelog-standard conventions

When ready to release to npm:

1. git checkout master
2. git pull origin master
3. yarn release:dryrun
4. yarn release
5. Engage pre-publication paranoia
6. git push --follow-tags origin master
7. npm publish - not yarn here as yarn doesn't seem to respect publishConfig

MIT © David Smith