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๐Ÿ‡ฎ๐Ÿ‡ฑ React Next 2022

๐Ÿ‡ฎ๐Ÿ‡ฑ React Nextย 2022

โ„น๏ธ Inside Fiber: the in-depth overview you wanted a TLDR for

We'll have an in-depth overview of the important concepts behind reconciliation and React Fiber. Then, we'll explore how React uses this algorithm and go through a few magic words we hear a lot, like coroutines, continuations, generators, and algebraic effectsโ€”and see how they all relate to React.

Matheus Albuquerque

June 28, 2022
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  1. Hello, React Next ๐Ÿ™‹ ๐Ÿ‡ฎ๐Ÿ‡ฑ ๐ŸŒŽ INSIDE FIBER: THE IN-DEPTH

    OVERVIEW YOU WANTED A TLDR FOR โ€ข THE 28TH OF JUNE, 2022.
  2. Iโ€™M MATHEUS ๐Ÿ™‹ โ† @YTHECOMBINATOR ON THE WEB โ† SR.

    SOFTWARE ENGINEER @ MEDALLIA โ† MENTOR @ TECHLABS BERLIN
  3. 2. MAYBE THIS TALK WONโ€™T BE 100% WHAT YOUโ€™D CALL

    A TLDR ๐Ÿคฏ= HUGE CONTENT PAYLOAD / DESERVES FURTHER DISCUSSIONS AFTER THE SESSION
  4. let frame: Frame = { return: frame, fn: add, parameters:

    [2, 2], localVariables: { result: 4, }, }
  5. let frame: Frame = { return: frame, fn: add, parameters:

    [2, 2], localVariables: { result: 4, }, } let fiber: Fiber = { return: fiber, component: Avatar, props: { id: 4 }, state: { isLoaded: true, }, }
  6. โ† FIBER ARCHITECTURE โ‡ข REACT-SPECIFIC IMPLEMENTATION OF A CALL-STACK-LIKE MODEL

    WHERE REACT HAS FULL CONTROL OF SCHEDULING WHAT SHOULD BE DONE โ† FIBER โ‡ข A STACK FRAME FOR A REACT COMPONENT
  7. DURING RECONCILIATION, DATA FROM EVERY REACT ELEMENT RETURNED FROM THE

    RENDER METHOD IS MERGED INTO THE TREE OF FIBER NODES. DEPENDING ON THE TYPE OF A REACT ELEMENT THE FRAMEWORK NEEDS TO PERFORM DIFFERENT ACTIVITIES. EACH ELEMENT IS CONVERTED INTO A FIBER NODE THAT DESCRIBES THE WORK THAT NEEDS TO BE DONE. ONCE A TEMPLATE GOES THROUGH THE JSX COMPILER, YOU END UP WITH A BUNCH OF REACT ELEMENTS.
  8. DURING RECONCILIATION, DATA FROM EVERY REACT ELEMENT RETURNED FROM THE

    RENDER METHOD IS MERGED INTO THE TREE OF FIBER NODES. DEPENDING ON THE TYPE OF A REACT ELEMENT THE FRAMEWORK NEEDS TO PERFORM DIFFERENT ACTIVITIES. EACH ELEMENT IS CONVERTED INTO A FIBER NODE THAT DESCRIBES THE WORK THAT NEEDS TO BE DONE. ONCE A TEMPLATE GOES THROUGH THE JSX COMPILER, YOU END UP WITH A BUNCH OF REACT ELEMENTS.
  9. DEPENDING ON THE TYPE OF A REACT ELEMENT THE FRAMEWORK

    NEEDS TO PERFORM DIFFERENT ACTIVITIES. EACH ELEMENT IS CONVERTED INTO A FIBER NODE THAT DESCRIBES THE WORK THAT NEEDS TO BE DONE. ONCE A TEMPLATE GOES THROUGH THE JSX COMPILER, YOU END UP WITH A BUNCH OF REACT ELEMENTS. DURING RECONCILIATION, DATA FROM EVERY REACT ELEMENT RETURNED FROM THE RENDER METHOD IS MERGED INTO THE TREE OF FIBER NODES.
  10. EACH ELEMENT IS CONVERTED INTO A FIBER NODE THAT DESCRIBES

    THE WORK THAT NEEDS TO BE DONE. ONCE A TEMPLATE GOES THROUGH THE JSX COMPILER, YOU END UP WITH A BUNCH OF REACT ELEMENTS. DURING RECONCILIATION, DATA FROM EVERY REACT ELEMENT RETURNED FROM THE RENDER METHOD IS MERGED INTO THE TREE OF FIBER NODES. DEPENDING ON THE TYPE OF A REACT ELEMENT THE FRAMEWORK NEEDS TO PERFORM DIFFERENT ACTIVITIES.
  11. ONCE A TEMPLATE GOES THROUGH THE JSX COMPILER, YOU END

    UP WITH A BUNCH OF REACT ELEMENTS. DURING RECONCILIATION, DATA FROM EVERY REACT ELEMENT RETURNED FROM THE RENDER METHOD IS MERGED INTO THE TREE OF FIBER NODES. DEPENDING ON THE TYPE OF A REACT ELEMENT THE FRAMEWORK NEEDS TO PERFORM DIFFERENT ACTIVITIES. A UNIT OF WORK. EACH ELEMENT IS CONVERTED INTO A FIBER NODE THAT DESCRIBES THE WORK THAT NEEDS TO BE DONE.
  12. ONCE A TEMPLATE GOES THROUGH THE JSX COMPILER, YOU END

    UP WITH A BUNCH OF REACT ELEMENTS. DURING RECONCILIATION, DATA FROM EVERY REACT ELEMENT RETURNED FROM THE RENDER METHOD IS MERGED INTO THE TREE OF FIBER NODES. DEPENDING ON THE TYPE OF A REACT ELEMENT THE FRAMEWORK NEEDS TO PERFORM DIFFERENT ACTIVITIES. A UNIT OF WORK. EACH ELEMENT IS CONVERTED INTO A FIBER NODE THAT DESCRIBES THE WORK THAT NEEDS TO BE DONE. AND THAT MAKES IT A CONVENIENT WAY TO TRACK, SCHEDULE, PAUSE AND ABORT THE WORK.
  13. let fiberNode = fiberRoot.current; let fibersMap = new Map(); while

    (fiberNode) { if (fiberNode.stateNode ! = = null) { fibersMap.set(fiberNode.stateNode, fiberNode); } if (fiberNode.child === null) { while (fiberNode ! = = null & & fiberNode.sibling === null) { fiberNode = fiberNode.return; } fiberNode = fiberNode?.sibling; continue; } fiberNode = fiberNode.child; }
  14. let fiberNode = fiberRoot.current; let fibersMap = new Map(); while

    (fiberNode) { if (fiberNode.stateNode ! = = null) { fibersMap.set(fiberNode.stateNode, fiberNode); } if (fiberNode.child === null) { while (fiberNode ! = = null & & fiberNode.sibling === null) { fiberNode = fiberNode.return; } fiberNode = fiberNode?.sibling; continue; } fiberNode = fiberNode.child; } ๐Ÿคฏ
  15. IT CAN BE THOUGHT OF AS A LIST WITH THREE

    ELEMENTS โ† A SYMBOL NAMED LET โ† A VECTOR WITH TWO ELEMENTS โ† A SYMBOL NAMED X โ† AND AN INTEGER โ† A LIST WITH TWO ELEMENTS โ† A SYMBOL NAMED INC โ† AND A SYMBOL NAMED X
  16. โ€œโ€ฆHOMOICONICITY IS A PROPERTY OF SOME PROGRAMMING LANGUAGES IN WHICH

    THE CODE USED TO EXPRESS A PROGRAM IS WRITTEN USING THE DATA STRUCTURES OF THAT LANGUAGE. ๐Ÿคฏ
  17. CODE = DATA โ€œโ€ฆHOMOICONICITY IS A PROPERTY OF SOME PROGRAMMING

    LANGUAGES IN WHICH THE CODE USED TO EXPRESS A PROGRAM IS WRITTEN USING THE DATA STRUCTURES OF THAT LANGUAGE. ๐Ÿคฏ
  18. โ† REACT ELEMENTS ARE JUST DATA โ† JUST LIKE IN

    LISP, REACT COMPONENTS CAN MANIPULATE THEIR CHILDREN AND RETURN COMPLETELY DIFFERENT THINGS
  19. / / . . . export function isWhen<Shape extends {}>(

    child: ElementWithMetadataUnion<Shape> ): child is ElementWithMetadata<WhenProps<Shape > > { return child.element.type === When; } / / . . . export function nodesToElementWithMetadata<Shape extends {}>( children: ReactNode ) { return Children.toArray(children).map((element, idx) = > ({ element: element, position: idx, })) as Array<ElementWithMetadata<Shape > > ; } / / . . .
  20. const supportsSensor = () = > Boolean(window.AmbientLightSensor); const AmbientLight =

    React.lazy(() = > import("./AmbientLight")); const Fallback = React.lazy(() = > import("./Fallback")); export default function MyComponent() { const { Match, When, Otherwise } = usePatternMatch(); return ( <Suspense fallback="Loading"> <Match> <When predicate={supportsSensor}> <AmbientLight /> </When> <Otherwise> <Fallback /> </Otherwise> </Match> </Suspense> ); }
  21. const supportsSensor = () = > Boolean(window.AmbientLightSensor); const AmbientLight =

    React.lazy(() = > import("./AmbientLight")); const Fallback = React.lazy(() = > import("./Fallback")); export default function MyComponent() { const { Match, When, Otherwise } = usePatternMatch(); return ( <Suspense fallback="Loading"> <Match> <When predicate={supportsSensor}> <AmbientLight /> </When> <Otherwise> <Fallback /> </Otherwise> </Match> </Suspense> ); } PATTERN MATCHING + REACT.SUSPENSE + REACT.LAZY() = USERS DOWNLOAD ONLY THE ACTUAL COMPONENT BUNDLE THAT MATCHES A CONDITION
  22. const supportsSensor = () = > Boolean(window.AmbientLightSensor); const AmbientLight =

    React.lazy(() = > import("./AmbientLight")); const Fallback = React.lazy(() = > import("./Fallback")); export default function MyComponent() { const { Match, When, Otherwise } = usePatternMatch(); return ( <Suspense fallback={"Loading"}> <Match> <When predicate={supportsSensor}> <AmbientLight /> </When> <Otherwise> <Fallback /> </Otherwise> </Match> </Suspense> ); } PATTERN MATCHING + REACT.SUSPENSE + REACT.LAZY() = USERS DOWNLOAD ONLY THE ACTUAL COMPONENT BUNDLE THAT MATCHES A CONDITION MANIPULATING BASED ON ELEMENTS DATA.
  23. 1. A GENERATOR (PRODUCER) THAT CAN ALSO CONSUME VALUES. โ†

    JAVASCRIPT GENERATORS CAN CONSUME VALUES โ† BY THIS DEFINITION, THEY ARE COROUTINES
  24. 2. โ† THIS IS THE MOST COMMON MEANING OF โ€œCOROUTINEโ€

    IN THE JAVASCRIPT WORLD โ† WE HAD CO AND BLUEBIRD, WHICH HAD ASYNC/AWAIT IMPLEMENTATIONS BASED ON GENERATORS A GENERATOR THAT CAN RESOLVE ASYNCHRONOUS VALUES, LIKE ASYNC/AWAIT.
  25. 3. โ† = DEEP AWAIT โ† WITH SUSPENSE, WE CAN

    PAUSE RECONCILIATION AT ANY DEPTH A GENERATOR THAT CAN YIELD WITH A STACKFUL CONTINUATION ๐Ÿคฏ
  26. Fibers CONTROL IS PASSED TO A SCHEDULER WHICH DETERMINES WHAT

    TO RUN NEXT โ† = CONTROLLED AT THE LEVEL OF THE OPERATING SYSTEM OR FRAMEWORK โ† E.G. NODE.JS EVENT LOOP
  27. Coroutines CONTROL IS PASSED TO THE CALLER AND HANDLED BY

    APPLICATION CODE Fibers CONTROL IS PASSED TO A SCHEDULER WHICH DETERMINES WHAT TO RUN NEXT
  28. COROUTINES APPEARED WHEN WORK ON FIBER WAS FIRST GOING AS

    A SPECIFIC COMPONENT TYPE. THE IDEA BEHIND COROUTINESโ€Šโ€”โ€ŠAS OPPOSED TO FIBERSโ€Šโ€”โ€ŠWAS TO GIVE COMPONENTS EXPLICIT CONTROL OVER YIELDING AND RESUMPTION.
  29. โ† COROUTINES PER SI IN REACT NO LONGER EXIST. โ†

    IT WILL BE FASCINATING TO SEE WHAT FORM COROUTINES TAKE WHEN THEY RETURN TO REACT FIBER.
  30. function resourcefulOperation(value: number) { let newValue = String(value); for (let

    i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } function ResourcefulComponent(props: { value: number }) { const { value } = props; const result = resourcefulOperation(value); return <p>{result}</p>; }
  31. function resourcefulOperation(value: number) { let newValue = String(value); for (let

    i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } function ResourcefulComponent(props: { value: number }) { const { value } = props; const result = resourcefulOperation(value); return <p>{result}</p>; }
  32. function* resourcefulOperation(value: number) { let newValue = String(value); while (true)

    { yield; for (let i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } } const initialValue = 0; const scheduler = new Scheduler(resourcefulOperation, initialValue); function ResourcefulComponent(props: { value: number }) { const { value } = props; const result = scheduler.performUnitOfWork(value); return <p>{result}</p>; }
  33. function* resourcefulOperation(value: number) { let newValue = String(value); while (true)

    { yield; for (let i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } } const initialValue = 0; const scheduler = new Scheduler(resourcefulOperation, initialValue); function ResourcefulComponent(props: { value: number }) { const { value } = props; const result = scheduler.performUnitOfWork(value); return <p>{result}</p>; } / / PROMOTED TO A GENERATOR. / / YIELDING INSIDE AN INFINITE LOOP. / / DOING CONCURRENT STUFF.
  34. enum SchedulerState { IDLE = "IDLE", PENDING = "PENDING", DONE

    = "DONE", } class Scheduler<T> { state: SchedulerState; result: T; worker: (data: T) = > Generator; iterator: Generator; constructor(worker: (data: T) = > Generator, initialResult: T) { this.state = SchedulerState.IDLE; this.worker = worker; this.result = initialResult; } performUnitOfWork(data: T) { switch (this.state) { case "IDLE": this.state = SchedulerState.PENDING; this.iterator = this.worker(data); throw Promise.resolve(); case "PENDING": const { value, done } = this.iterator.next(); if (done) { this.result = value; this.state = SchedulerState.DONE; return value; } throw Promise.resolve(); case "DONE": this.state = SchedulerState.IDLE; return this.result; } } } ๐Ÿคฏ
  35. enum SchedulerState { IDLE = "IDLE", PENDING = "PENDING", DONE

    = "DONE", } class Scheduler<T> { state: SchedulerState; result: T; worker: (data: T) = > Generator; iterator: Generator; constructor(worker: (data: T) = > Generator, initialResult: T) { this.state = SchedulerState.IDLE; this.worker = worker; this.result = initialResult; } performUnitOfWork(data: T) { switch (this.state) { case "IDLE": this.state = SchedulerState.PENDING; this.iterator = this.worker(data); throw Promise.resolve(); case "PENDING": const { value, done } = this.iterator.next(); if (done) { this.result = value; this.state = SchedulerState.DONE; return value; } throw Promise.resolve(); case "DONE": this.state = SchedulerState.IDLE; return this.result; } } } ๐Ÿคฏ
  36. function resourcefulOperation(value: number) { let newValue = String(value); for (let

    i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } function ResourcefulComponent(props: { value: number }) { const { value } = props; const result = resourcefulOperation(value); return <p>{result}</p>; }
  37. function resourcefulOperation(value: number) { let newValue = String(value); for (let

    i = 0; i < 1000000; i++) { newValue = `${value} + ${i} = ${value + i}`; } return newValue; } function ResourcefulComponent(props: { value: number }) { const [_, startTransition] = useTransition(); const [result, setResult] = useState(""); useEffect(() = > { startTransition(() = > { const newResult = resourcefulOperation(props.value); setResult(newResult); }); }, [props.value]); return <p>{result}</p>; }
  38. โ† THEREโ€™S NO USE OF WORKERS OR WASM FOR PARALLELISM

    โ† THEREโ€™S A COOPERATIVE MULTITASKING MODEL โ† A SINGLE RENDERING THREAD, BUT INTERRUPTIBLE SO THAT RENDERING CAN BE INTERLEAVED WITH OTHER MAIN THREAD TASKS AND OTHER REACT RENDERS
  39. โ†“ ORIGINAL RENDER TASK USER INPUT โ†’ โ†‘ HIGHER PRIORITY

    RENDER TASK โ†“ RESUME ORIGINAL RENDER TASK
  40. โ† AN UPDATE CAN HAPPEN IN THE BACKGROUND, WITHOUT BLOCKING

    ANOTHER IN RESPONSE TO NEW INPUT โ† THE SCHEDULER SWITCHES TO THE MORE URGENT RENDERING TASK, THEN PICKS THE ORIGINAL TASK UP AFTER THAT HAS FINISHED
  41. โ† IT YIELDS EXECUTION IS BACK TO THE MAIN THREAD

    EVERY 5MS โ† IT'S SMALLER THAN A SINGLE FRAME EVEN ON 120FPS DEVICES, SO IT WON'T BLOCK ANIMATIONS โ† MOST INDIVIDUAL COMPONENTS DON'T TAKE LONGER THAN A SINGLE FRAME TO RENDER โ† IN PRACTICE, RENDERING IS EFFECTIVELY INTERRUPTIBLE
  42. โ† ASYNCHRONY IN JAVASCRIPT IS CONTAGIOUS โ† IF ANY FUNCTION

    IS ASYNC, THEN EVERYTHING THAT CALLS IT MUST ALSO BE ASYNCโ€ฆ โ† โ€ฆAND SO ON UNTIL THE ENTIRE PROGRAM IS ASYNCHRONOUS ๐Ÿคท
  43. โ† ASYNCHRONY IN JAVASCRIPT ISNโ€™T FREE โ† EVERY ASYNCHRONOUS FUNCTION

    CALL HAS TO: โ† ALLOCATE CALLBACKS โ† STORE THEM SOMEWHERE โ† AND TAKE A TRIP BACK TO THE EVENT LOOP BEFORE INVOKING THOSE CALLBACKS
  44. โ† ITS API HAS TWO MAIN FUNCTIONS FOR COMPILING SASS

    FILES: ONE SYNC AND ONE ASYNC โ† THE ASYNC ONE BECAME WIDELY USED IN PRACTICE BECAUSE IT ENABLED ASYNC PLUGINS (E.G. WEBPACKโ€™S SASS-LOADER)
  45. โ† FOR NODE SASS, THE PERFORMANCE DIFFERENCE WAS NEGLIGIBLE, BECAUSE

    IT WAS BUILT ON C++ โ† HOWEVER, DART SASS RUNS AS PURE JAVASCRIPT, WHICH MAKES IT SUBJECT TO JAVASCRIPTโ€™S ASYNC RULES
  46. โ† THE ASYNC VERSION IN DART SASS WAS 2-3X SLOWER

    THAN THE SYNC ONE โ† THEY STARTED USING NODE-FIBERS TO IMPLEMENT THE ASYNC API USING THE FAST, SYNC, CODE
  47. โ† EFFECTS ASK THE CALLING ENVIRONMENT TO HANDLE A PARTICULAR

    TASK โ† WHEN AN EFFECT IS USED, THE NEAREST EFFECT HANDLER IS CALLED, WHICH ALLOWS YOU TO RUN CODE IN RESPONSE TO THE EFFECT AND RETURN SOME VALUE. ๐Ÿคฏ
  48. function getName(user) { let name = user.name; if (name ===

    null) { name = perform 'ask_name'; } return name; } const arya = { name: null, friendNames: [] }; const gendry = { name: 'Gendry', friendNames: [] }; try { getName(arya); } handle (effect) { if (effect === 'ask_name') { resume with 'Arya Stark'; } }
  49. function getName(user) { let name = user.name; if (name ===

    null) { name = perform 'ask_name'; } return name; } const arya = { name: null, friendNames: [] }; const gendry = { name: 'Gendry', friendNames: [] }; try { getName(arya); } handle (effect) { if (effect === 'ask_name') { resume with 'Arya Stark'; } }
  50. function getName(user) { let name = user.name; if (name ===

    null) { name = perform 'ask_name'; } return name; } const arya = { name: null, friendNames: [] }; const gendry = { name: 'Gendry', friendNames: [] }; try { getName(arya); } handle (effect) { if (effect === 'ask_name') { resume with 'Arya Stark'; } } / / THROW โ†’ PERFORM / / CATCH โ†’ HANDLE / / LETS US JUMP BACK TO WHERE WE PERFORMED THE EFFECT
  51. function ThemeBorderColorRequest() { } function FancyBox(children) { const color =

    raise new ThemeBorderColorRequest(); return { borderWidth: '1px', borderColor: color, children: children }; } function BlueTheme(children) { return try { children(); } catch effect ThemeBorderColorRequest - > [, continuation] { continuation('blue'); } } function App(data) { return BlueTheme( FancyUserList.bind(null, data.users) ); }
  52. function ThemeBorderColorRequest() { } function FancyBox(children) { const color =

    raise new ThemeBorderColorRequest(); return { borderWidth: '1px', borderColor: color, children: children }; } function BlueTheme(children) { return try { children(); } catch effect ThemeBorderColorRequest - > [, continuation] { continuation('blue'); } } function App(data) { return BlueTheme( FancyUserList.bind(null, data.users) ); } / / THROW โ†’ RAISE / / CATCH โ†’ CATCH EFFECT
  53. A COMPONENT IS ABLE TO SUSPEND THE FIBER IT IS

    RUNNING IN BY THROWING A PROMISE, WHICH IS CAUGHT AND HANDLED BY THE FRAMEWORK.
  54. THROW โ†’ HANDLE โ†’ RESUME PATTERN. A COMPONENT IS ABLE

    TO SUSPEND THE FIBER IT IS RUNNING IN BY THROWING A PROMISE, WHICH IS CAUGHT AND HANDLED BY THE FRAMEWORK.
  55. 1. REACT FIBER WAS A REWRITE OF REACT FOCUSED ON

    GIVING MORE LOW-LEVEL CONTROL OVER PROGRAM EXECUTION
  56. 1. โ† FIBERS AS A LOW-LEVEL COOPERATIVE WAY TO MODEL

    EXECUTION โ† ALGEBRAIC EFFECTS AS A WAY TO HANDLE EFFECTS WHERE THESE AND THEIR BEHAVIOR ARE INDEPENDENT LOW-LEVEL CONTROL OVER PROGRAM EXECUTION
  57. 2. REACT TRIES TO ADDRESS THE LACK OF SOME JAVASCRIPT

    FEATURES/LANGUAGE-LEVEL RESOURCES BY IMPLEMENTING SOME ALTERNATIVE SOLUTIONS TO ACHIEVE SIMILAR BEHAVIORS
  58. 5. THE FACT WE'RE DISCUSSING ALL OF THESE TOPICS SHOWS

    THAT REACT ACTS AS A DEMOCRATIC AGENT FOR THIS KIND OF KNOWLEDGE IN THE FRONT-END WORLD
  59. THIS IS THE EIGHT-YEARS-AGO-ME GIVING A TALK ABOUT IONIC AT

    AN IOS DEVELOPERS MEETUP TELLING THEM THAT ANGULAR WOULD BE THE FUTURE.