setState Machine

What if your components' state was deterministic?
Learn about the implementation of State Machines to manage React Components' state - from the basics of Automata theory to autogenerated tests.

1. setState Machine @MicheleBertoli
2. I’m Michele, a React fanboy
3. I work in Ads at Facebook and I build user interfaces
4. State is hard
5. Infinite Scroll • Attach an event handler to scroll • Check if the user scrolled > 90% • Fetch more data
6. if (scrollPercentage > 0.9) { this.fetch() }
7. if ( scrollPercentage > 0.9 && !this.state.isFetching ) { this.fetch() }
8. {this.state.isFetching ? 'Loading...' : null}
9. if (!data.hasMore) { this.detach() }
10. {this.state.hasError ? 'Something went wrong' : null}
11. {isEmpty ? (isFetching ? <h2>Loading...</h2> : <h2>Empty.</h2>) : <div style={{ opacity: isFetching ? 0.5 : 1 }}> <Posts posts={posts} /> </div> } source: github.com/reactjs/redux
12. Bottom-up • Focus on linear transitions • Hard to understand • Edge cases
13. State Machine
14. Automata Theory • Abstract machines • Deterministic finite automata • <Q, Σ, δ, q0, F>
15. A B C α β
16. SEMI NO-SEMI TOGGLE TOGGLE
17. SEMI SPACE SEMI TAB NO-SEMI TAB NO-SEMI SPACE TOGGLE SEMI TOGGLE SEMI USE TAB USE TAB
18. Statecharts
19. “A visual formalism for complex systems.” David Harel, 1987
20. Statecharts Extension of the conventional formalism of state machines and state diagrams
21. Clustering
22. C A B β β α
23. β C A B α
24. β C D
25. Orthogonality
26. A B C D
27. Guards
28. A B event [guard]
29. Actions
30. A B event / action
31. A entry action1 exit action2, action3
32. Workflow
33. Statechart Event Actions
34. “A statechart is a magic-box: you tell it what happened, and it tells you what to do.” Luca Matteis, 2018
35. yarn add xstate
36. xstate Functional, Stateless JS Finite State Machines and Statecharts
37. entry removeSemicolons entry addSemicolons noSemi semi TOGGLE TOGGLE
38. const prettyMachine = Machine({ initial: 'semi', states: { semi, noSemi, }, })
39. const semi = { on: { TOGGLE: 'noSemi' }, onEntry: 'addSemicolons', }
40. const noSemi = { on: { TOGGLE: 'semi' }, onEntry: 'removeSemicolons', }
41. const { actions } = prettyMachine .transition('semi', 'TOGGLE') // => ["removeSemicolons"]
42. yarn add react-automata
43. react-automata A state machine abstraction for React
44. start entry attach listening SUCCESS [hasMore] ERROR / error SCROLL [scrollPercentage > 0.9] READY fetching entry fetch finish SUCCESS [!hasMore] entry detach
45. withStatechart(statechart)(MyInfiniteScroll)
46. start entry attach listening finish SUCCESS [!hasMore] SUCCESS [hasMore] ERROR / error SCROLL [scrollPercentage > 0.9] READY fetching entry fetch entry detach
47. class MyInfiniteScroll extends React.Component { attach() {} // render() {} }
48. attach() { this.element.addEventListener( 'scroll', this.handleScroll ) }
49. start entry attach READY SUCCESS [hasMore] listening finish SUCCESS [!hasMore] ERROR / error SCROLL [scrollPercentage > 0.9] fetching entry fetch entry detach
50. this.props.transition('READY')
51. ERROR / error SUCCESS [!hasMore] SUCCESS [hasMore] entry fetch fetching READY start entry attach listening finish SCROLL [scrollPercentage > 0.9] entry detach
52. class MyInfiniteScroll extends React.Component { attach() {} fetch() {} // render() {} }
53. fetch() { const { transition } = this.props loadData() .then(data => transition('SUCCESS', data) .catch(() => transition('ERROR')) }
54. Workflow
55. React Automata Transition (evt, data) Action Methods
56. withStatechart(statechart, { devTools: true })( MyInfiniteScroll )
57. <Action show="fetch"> Loading… </Action>
58. “The best testing strategy is not writing tests.” Michele Bertoli, 2016
59. testStatechart({ statechart }, MyInfiniteScroll)
60. exports[`fetching`] = ` <div> Loading... </div> `;
61. exports[`error`] = ` <div> Something went wrong </div> `;
62. Benefits • Fewer bugs • Easy to understand • What vs when
63. “2018 front-end trend prediction: Everybody's going to start using state machines for UIs.” Max Stoiber, 2018
64. bit.ly/automata-calculator
65. Takeaways • States > Transitions • Top-down • Read more papers
66. Constructing the User Interface with Statecharts Ian Horrocks, 1998 bit.ly/statecharts-book Statecharts: A Visual Formalism for Complex Systems David Harel, 1987 bit.ly/statecharts-paper
67. T @gandellinux @DavidKPiano @ryanflorence @mogsie
68. @MicheleBertoli