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| 1 | +import { FC, useEffect, useState, Suspense, use, useMemo, useRef, ReactNode, Children, useReducer, useCallback } from 'react' |
| 2 | + |
| 3 | +declare module 'react' { |
| 4 | + export function use<T>(x: Promise<T>): T | undefined; |
| 5 | +} |
| 6 | + |
| 7 | +const PickChild: FC<{ n: number; children: ReactNode }> = ({ n, children }) => |
| 8 | + Children.toArray(children)[n]; |
| 9 | + |
| 10 | +const IfElse: FC<{ condition: boolean; children: [ReactNode, ReactNode] }> = ({ condition, children }) => |
| 11 | + <PickChild n={+!condition}>{children}</PickChild>; |
| 12 | + |
| 13 | +const CallFunction: FC<{ fn: () => void }> = ({ fn }) => { |
| 14 | + const fnRef = useRef(fn); |
| 15 | + fnRef.current = fn; |
| 16 | + useEffect(() => fnRef.current(), []); |
| 17 | + return null; |
| 18 | +} |
| 19 | + |
| 20 | +const Factorial: FC<any> = ({ n, resolve }) => { |
| 21 | + const [count, setCount] = useState(n) |
| 22 | + const [result, setResult] = useState(1) |
| 23 | + |
| 24 | + useEffect(() => { |
| 25 | + setCount(count - 1) |
| 26 | + setResult(result => count * result) |
| 27 | + }, [count, resolve, result]) |
| 28 | + |
| 29 | + return ( |
| 30 | + <> |
| 31 | + Calculating factorial of {n}... |
| 32 | + <IfElse condition={count > 1}> |
| 33 | + <CallFunction fn={() => resolve(result)} /> |
| 34 | + <></> |
| 35 | + </IfElse> |
| 36 | + </> |
| 37 | + ) |
| 38 | +} |
| 39 | + |
| 40 | +const ShowResult: FC<{ promise: Promise<any> }> = ({ promise }) => { |
| 41 | + const result = use(promise); |
| 42 | + return <>Result: {result}</> |
| 43 | +} |
| 44 | + |
| 45 | +const App: FC = () => { |
| 46 | + const [_, forceUpdate] = useReducer((n) => n + 1, 0) |
| 47 | + const resolve = useRef((_: any) => {}); |
| 48 | + const promise = useMemo(() => { |
| 49 | + return new Promise((res) => { |
| 50 | + resolve.current = res |
| 51 | + }) |
| 52 | + }, []) |
| 53 | + |
| 54 | + const onReturn = useCallback((n: number) => { |
| 55 | + resolve.current(n) |
| 56 | + forceUpdate() |
| 57 | + }, []) |
| 58 | + |
| 59 | + return ( |
| 60 | + <Suspense fallback={<Factorial n={5} resolve={onReturn} />}> |
| 61 | + <ShowResult promise={promise} /> |
| 62 | + </Suspense> |
| 63 | + ) |
| 64 | +} |
| 65 | + |
| 66 | +export default App |
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