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| import { useState, useEffect } from 'melody-hooks'; | |
| const canUseIntersectionObserver = window.IntersectionObserver !== undefined; | |
| const useIsVisibleFallback = () => true; | |
| export const createUseIsVisible = options => { | |
| if (!canUseIntersectionObserver) { | |
| return useIsVisibleFallback; | |
| } | |
| const listenersByElement = new WeakMap(); | |
| const handleChange = entries => { | |
| for (let i = 0, l = entries.length; i < l; i++) { | |
| const entry = entries[i]; | |
| const { target } = entry; | |
| const listeners = listenersByElement.get(target); | |
| if (!listeners || !listeners.length) { | |
| continue; | |
| } | |
| for (let j = 0, jl = listeners.length; j < jl; j++) { | |
| const listener = listeners[j]; | |
| if (typeof listener !== 'function') { | |
| listener(entry.isIntersecting); | |
| } | |
| } | |
| } | |
| }; | |
| const observer = new IntersectionObserver(handleChange, options); | |
| const subscribe = (el, listener) => { | |
| let listeners = listenersByElement.get(el); | |
| if (!listeners) { | |
| listeners = []; | |
| listenersByElement.set(el, listeners); | |
| observer.observe(el); | |
| } | |
| listeners.push(listener); | |
| return () => { | |
| const index = listeners.indexOf(listener); | |
| if (listeners > -1) { | |
| listeners.splice(index, 1); | |
| } | |
| if (listeners.length) { | |
| listenersByElement.delete(el); | |
| observer.unobserve(el); | |
| } | |
| }; | |
| }; | |
| return (ref, initialEntry = false) => { | |
| const [isIntersecting, setIsIntersecting] = useState(initialEntry); | |
| useEffect(() => subscribe(ref.current, setIsIntersecting), [ref]); | |
| return isIntersecting; | |
| }; | |
| }; | |
| export const useIsVisible = createUseIsVisible({ | |
| threshold: [0, 0.75], | |
| rootMargin: '500px 0px', | |
| }); |
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