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Last active March 5, 2023 21:24
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import { useState, useEffect, useRef } from 'react';
// Usage
function App() {
// Ref for the element that we want to detect whether on screen
const ref = useRef();
// Call the hook passing in ref and root margin
// In this case it would only be considered onScreen if more ...
// ... than 300px of element is visible.
const onScreen = useOnScreen(ref, '-300px');
return (
<div style={{ height: '100vh' }}>
<h1>Scroll down to next section 👇</h1>
height: '100vh',
backgroundColor: onScreen ? '#23cebd' : '#efefef'
{onScreen ? (
<h1>Hey I'm on the screen</h1>
<img src="" />
) : (
<h1>Scroll down 300px from the top of this section 👇</h1>
// Hook
function useOnScreen(ref, rootMargin = '0px') {
// State and setter for storing whether element is visible
const [isIntersecting, setIntersecting] = useState(false);
useEffect(() => {
const observer = new IntersectionObserver(
([entry]) => {
// Update our state when observer callback fires
if (ref.current) {
return () => {
}, []); // Empty array ensures that effect is only run on mount and unmount
return isIntersecting;
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I agree. I do believe ref.current should be passed as argument of useEffect line 58. Currently if the ref changes, nothing happens and the previous is leaked.

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You may also consider returning the ref from the hook instead of passing it as argument, c.f.

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In the useEffect, we should keep a reference to the ref.current like this: const currentRef = ref.current.

Then do: observer.unobserve(currentRef);

In doing so, we will ensure that ref.current doesn't end up changing before this cleanup is run.

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