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A hook to observe the intersection of elements and return the IDs of those that are intersecting.
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| import { useEffect, useState } from "react"; | |
| /** | |
| * A hook to observe the intersection of elements and return the IDs of those | |
| * that are intersecting. | |
| * @param ids The IDs of the elements to observe | |
| * @param options The options to pass to the IntersectionObserver | |
| * | |
| * @example | |
| * ```tsx | |
| * const [activeId, ...otherIntersectingIds] = useIntersecting(ids, { | |
| * threshold: 0.5, | |
| * }); | |
| * ``` | |
| * | |
| * @see | |
| * https://developer.mozilla.org/en-US/docs/Web/API/Intersection_Observer_API | |
| */ | |
| export function useIntersecting( | |
| ids: string[], | |
| { | |
| root = null, | |
| rootMargin = "0px", | |
| /** | |
| * The threshold (0-1) at which to trigger the intersection observer. A | |
| * value of 1 means the entire element must be visible, while 0 means any | |
| * part of the element being visible will trigger the observer. | |
| */ | |
| threshold = 0.0, | |
| }: IntersectionObserverInit = {}, | |
| ) { | |
| const [intersectingIds, setIntersectingIds] = useState<string[]>([]); | |
| useEffect(() => { | |
| const observer = new IntersectionObserver( | |
| (entries) => { | |
| const isIntersectingById = Object.fromEntries( | |
| entries.map((entry) => [entry.target.id, entry.isIntersecting]), | |
| ); | |
| setIntersectingIds((previousIds) => { | |
| return ids.filter((id) => { | |
| if (id in isIntersectingById) { | |
| return isIntersectingById[id]; | |
| } | |
| // No change in intersection status for this ID | |
| return previousIds?.includes(id); | |
| }); | |
| }); | |
| }, | |
| { root, rootMargin, threshold }, | |
| ); | |
| for (const id of ids) { | |
| const element = document.getElementById(id); | |
| if (element) { | |
| observer.observe(element); | |
| } | |
| } | |
| return () => observer.disconnect(); | |
| }, [ids]); | |
| return intersectingIds; | |
| } |
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