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Control <Image /> prefetching with React (#18904)
This pull request fixes `<Image />` not updating when new props are passed by removing external DOM mutations and relying on React to do it instead. As an added bonus, I've extracted the intersection observer from both the `<Image />` and `<Link />` component, as their instance can be shared! The increase in size is minor (+3B), and actually a decrease for apps using both `<Image />` and `<Link />`. --- Fixes #18698 Fixes #18369
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,102 @@ | ||
| import { useCallback, useEffect, useRef, useState } from 'react' | ||
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| type UseIntersectionObserverInit = Pick<IntersectionObserverInit, 'rootMargin'> | ||
| type UseIntersection = { disabled?: boolean } & UseIntersectionObserverInit | ||
| type ObserveCallback = (isVisible: boolean) => void | ||
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| const hasIntersectionObserver = typeof IntersectionObserver !== 'undefined' | ||
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| export function useIntersection<T extends Element>({ | ||
| rootMargin, | ||
| disabled, | ||
| }: UseIntersection): [(element: T | null) => void, boolean] { | ||
| const isDisabled = disabled || !hasIntersectionObserver | ||
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|
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| const unobserve = useRef<Function>() | ||
| const [visible, setVisible] = useState(false) | ||
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| const setRef = useCallback( | ||
| (el: T | null) => { | ||
| if (unobserve.current) { | ||
| unobserve.current() | ||
| unobserve.current = undefined | ||
| } | ||
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|
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| if (isDisabled || visible) return | ||
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| if (el && el.tagName) { | ||
| unobserve.current = observe( | ||
| el, | ||
| (isVisible) => isVisible && setVisible(isVisible), | ||
| { rootMargin } | ||
| ) | ||
| } | ||
| }, | ||
| [isDisabled, rootMargin, visible] | ||
| ) | ||
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|
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| useEffect(() => { | ||
| if (!hasIntersectionObserver) { | ||
| if (!visible) setVisible(true) | ||
| } | ||
| }, [visible]) | ||
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|
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| return [setRef, visible] | ||
| } | ||
|
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| function observe( | ||
| element: Element, | ||
| callback: ObserveCallback, | ||
| options: UseIntersectionObserverInit | ||
| ) { | ||
| const { id, observer, elements } = createObserver(options) | ||
| elements.set(element, callback) | ||
|
|
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| observer.observe(element) | ||
| return function unobserve() { | ||
| observer.unobserve(element) | ||
|
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| // Destroy observer when there's nothing left to watch: | ||
| if (elements.size === 0) { | ||
| observer.disconnect() | ||
| observers.delete(id) | ||
| } | ||
| } | ||
| } | ||
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| const observers = new Map< | ||
| string, | ||
| { | ||
| id: string | ||
| observer: IntersectionObserver | ||
| elements: Map<Element, ObserveCallback> | ||
| } | ||
| >() | ||
| function createObserver(options: UseIntersectionObserverInit) { | ||
| const id = options.rootMargin || '' | ||
| let instance = observers.get(id) | ||
| if (instance) { | ||
| return instance | ||
| } | ||
|
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| const elements = new Map<Element, ObserveCallback>() | ||
| const observer = new IntersectionObserver((entries) => { | ||
| entries.forEach((entry) => { | ||
| const callback = elements.get(entry.target) | ||
| const isVisible = entry.isIntersecting || entry.intersectionRatio > 0 | ||
| if (callback && isVisible) { | ||
| callback(isVisible) | ||
| } | ||
| }) | ||
| }, options) | ||
|
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| observers.set( | ||
| id, | ||
| (instance = { | ||
| id, | ||
| observer, | ||
| elements, | ||
| }) | ||
| ) | ||
| return instance | ||
| } |
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