React Automata

A state machine abstraction for React that provides declarative state management and automatic test generation.

Quick Start

Installation

yarn add react-automata

Usage

// App.js

import React from 'react'
import { Action, withStatechart } from 'react-automata'

export const statechart = {
  initial: 'a',
  states: {
    a: {
      on: {
        NEXT: 'b',
      },
      onEntry: 'enterA',
    },
    b: {
      on: {
        NEXT: 'a',
      },
      onEntry: 'enterB',
    },
  },
}

export class App extends React.Component {
  handleClick = () => {
    this.props.transition('NEXT')
  }

  render() {
    return (
      <div>
        <button onClick={this.handleClick}>NEXT</button>
        <Action show="enterA">Hello, A</Action>
        <Action show="enterB">Ciao, B</Action>
      </div>
    )
  }
}

export default withStatechart(statechart)(App)

// App.spec.js

import { testStatechart } from 'react-automata'
import { App, statechart } from './App'

test('it works', () => {
  testStatechart({ statechart }, App)
})

// App.spec.js.snap

exports[`it works: a 1`] = `
<div>
  <button
    onClick={[Function]}
  >
    NEXT
  </button>
  Hello, A
</div>
`;

exports[`it works: b 1`] = `
<div>
  <button
    onClick={[Function]}
  >
    NEXT
  </button>
  Ciao, B
</div>
`;

API

withStatechart(statechart[, options])(Component)

The withStatechart higher-order component takes a statechart definition (see xstate), some optional options and a component. It returns a new component with special props, action methods and lifecycle methods. The initial machine state and the initial data can be passed to the resulting component through the initialMachineState and initialData props.

Options

Option	Type	Description
devTools	bool	To connect the state machine to the Redux DevTools Extension.

Props

transition(event[, updater])

The method to change the state of the state machine. It takes an optional updater function that receives the previous data and returns a data change. The updater can also be an object, which gets merged into the current data.

handleClick = () => {
  this.props.transition('FETCH')
}

machineState

The current state of the state machine. Using this value is discouraged, as it couples the UI and the state machine.

<button onClick={this.handleClick}>
  {this.props.machineState === 'idle' ? 'Fetch' : 'Retry'}
</button>

Action methods

All the component's methods whose names match the names of the actions, are fired when the related transition happen. For example:

const statechart = {
  // ...
  fetching: {
    on: {
      SUCCESS: 'success',
      ERROR: 'error',
    },
    onEntry: 'enterFetching',
  },
  // ...
}

class App extends React.Component {
  // ...
  enterFetching() {
    fetch('https://api.github.com/users/gaearon/gists')
      .then(response => response.json())
      .then(gists => this.props.transition('SUCCESS', { gists }))
      .catch(() => this.props.transition('ERROR'))
  }
  // ...
}

Lifecycle methods

componentWillTransition(event)

The lifecycle method invoked when a transition is about to happen. It provides the event, and can be used to run side-effects.

componentWillTransition(event) {
  if (event === 'FETCH') {
    fetch('https://api.github.com/users/gaearon/gists')
      .then(response => response.json())
      .then(gists => this.props.transition('SUCCESS', { gists }))
      .catch(() => this.props.transition('ERROR'))
  }
}

componentDidTransition(prevStateMachine, event)

The lifecycle method invoked when a transition has happened and the state is updated. It provides the previous state machine, and the event. The current machineState is available in this.state.

componentDidTransition(prevStateMachine, event) {
  Logger.log(event)
}

<Action />

The component to define which parts of the tree should be rendered for a given action (or set of actions).

Prop	Type	Description
children	node	The children to be rendered when the conditions match.
hide	oneOfType(string, arrayOf(string))	The action(s) for which the children should be hidden.
render	func	The render prop receives a bool (true when the conditions match) and it takes precedence over children.
show	oneOfType(string, arrayOf(string))	The action(s) for which the children should be shown. When both `show` and `hide` are defined, the children are shown from the first `show` match to the first `hide` match.
onEnter	func	The function invoked when the component becomes visible, it provides the current machine state.
onLeave	func	The function invoked when the component becomes invisible, it provides the current machine state.

<Action show="enterError">Oh, snap!</Action>

<State />

The component to define which parts of the tree should be rendered for a given state (or set of states).

Prop	Type	Description
children	node	The children to be rendered when the conditions match.
render	func	The render prop receives a bool (true when the conditions match) and it takes precedence over children.
value	oneOfType(string, arrayOf(string))	The state(s) for which the children should be shown. It accepts the exact state, a glob expression or an array of states/expressions (e.g. `value="idle"`, `value="error."` or `value={['idle', 'error.']`).
onEnter	func	The function invoked when the component becomes visible, it provides the current machine state.
onLeave	func	The function invoked when the component becomes invisible, it provides the current machine state.

<State value="error">Oh, snap!</State>

testStatechart({ statechart[, fixtures] }, Component)

The method to automagically generate tests given a statechart definition, and a component. It accepts an optional fixtures configuration to describe which data should be injected into the component for a given transition.

const fixtures = {
  initialData: {
    gists: [],
  },
  fetching: {
    SUCCESS: {
      gists: [
        {
          id: 'ID1',
          description: 'GIST1',
        },
        {
          id: 'ID2',
          description: 'GIST2',
        },
      ],
    },
  },
}

test('it works', () => {
  testStatechart({ statechart, fixtures }, App)
})

Inspiration

Federico, for telling me "Hey, I think building UIs using state machines is the future".

David, for giving a very informative (and fun) talk about infinitely better UIs, and building xstate.

Ryan, for experimenting with xstate and React - Ryan's approach to React has always been a source of inspiration.

Erik, for writing about statecharts, and showing me how to keep UI and state machine decoupled.

brikou / react-automata