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Support multiple flush effects #39559

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merged 2 commits into from Aug 12, 2022
Merged

Support multiple flush effects #39559

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1fc4d35
Support multiple flush effects
huozhi Aug 12, 2022
97940a0
Merge branch 'canary' into multi-flush-effects
huozhi Aug 12, 2022
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16 changes: 6 additions & 10 deletions packages/next/server/app-render.tsx
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Expand Up @@ -1018,23 +1018,19 @@ export async function renderToHTMLOrFlight(
}
)

let flushEffectsHandler: (() => React.ReactNode) | null = null
const flushEffectsCallbacks: Set<() => React.ReactNode> = new Set()
function FlushEffects({ children }: { children: JSX.Element }) {
// Reset flushEffectsHandler on each render
flushEffectsHandler = null
const setFlushEffectsHandler = React.useCallback(
flushEffectsCallbacks.clear()
const addFlushEffects = React.useCallback(
(handler: () => React.ReactNode) => {
if (flushEffectsHandler)
throw new Error(
'The `useFlushEffects` hook cannot be used more than once.'
)
flushEffectsHandler = handler
flushEffectsCallbacks.add(handler)
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It will be added multiple times whenever a render happens I think?

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each render will use a new set, and those handles will only be collected once on server side

},
[]
)

return (
<FlushEffectsContext.Provider value={setFlushEffectsHandler}>
<FlushEffectsContext.Provider value={addFlushEffects}>
{children}
</FlushEffectsContext.Provider>
)
Expand Down Expand Up @@ -1063,7 +1059,7 @@ export async function renderToHTMLOrFlight(

const flushEffectHandler = (): string => {
const flushed = ReactDOMServer.renderToString(
<>{flushEffectsHandler && flushEffectsHandler()}</>
<>{Array.from(flushEffectsCallbacks).map((callback) => callback())}</>
)
return flushed
}
Expand Down
9 changes: 5 additions & 4 deletions packages/next/shared/lib/flush-effects.tsx
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Expand Up @@ -6,9 +6,10 @@ export const FlushEffectsContext = createContext<FlushEffectsHook | null>(
null as any
)

export function useFlushEffects(callbacks: () => React.ReactNode): void {
const flushEffectsImpl = useContext(FlushEffectsContext)
export function useFlushEffects(callback: () => React.ReactNode): void {
const addFlushEffects = useContext(FlushEffectsContext)
// Should have no effects on client where there's no flush effects provider
if (!flushEffectsImpl) return
return flushEffectsImpl(callbacks)
if (addFlushEffects) {
addFlushEffects(callback)
}
}
12 changes: 6 additions & 6 deletions test/e2e/app-dir/rsc-basic/app/root-style-registry.client.js
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Expand Up @@ -19,13 +19,13 @@ export default function RootStyleRegistry({ children }) {
return <>{styles}</>
}

// Allow multiple useFlushEffects
useFlushEffects(() => {
return (
<>
{styledJsxFlushEffect()}
{styledComponentsFlushEffect()}
</>
)
return <>{styledJsxFlushEffect()}</>
})

useFlushEffects(() => {
return <>{styledComponentsFlushEffect()}</>
})

// Only include style registry on server side for SSR
Expand Down