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Build infinite scroll in React by observing a small sentinel after the loaded items, then requesting another page when that sentinel enters the viewport or a scrollable container. IntersectionObserver detects visibility; your component or data layer still handles fetching, pagination, duplicate-request prevention, errors, and deciding when the feed ends.
What the component needs to manage
Keep pagination and rendering state separate from the observer. The data source supplies pages or cursors; the observer only signals when more data may be needed.
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- Items: the pages accumulated so far.
- Page or cursor: the position to request next, as defined by the data source.
- Loading and error state: whether a request is pending and whether it failed.
- Has-more state: whether the data source indicates another page exists.
The example below uses a page-based API that returns {"items": [...], "nextPage": 2}, or null for nextPage when no more pages remain. Adapt the response handling to your API; IntersectionObserver does not provide pagination or fetch data.
How to build the observer in React
Place a stable sentinel element after the list and attach a ref to it. Set up the observer in an effect, check isIntersecting, and disconnect it during cleanup. This example also uses a ref as an immediate request lock: state updates are asynchronous, so checking only a loading state may not prevent two callbacks from starting overlapping requests.
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import { useCallback, useEffect, useRef, useState } from "react";
export default function InfiniteList() {
const [items, setItems] = useState([]);
const [nextPage, setNextPage] = useState(1);
const [hasMore, setHasMore] = useState(true);
const [loading, setLoading] = useState(false);
const [error, setError] = useState(null);
const sentinelRef = useRef(null);
const requestInFlight = useRef(false);
const loadMore = useCallback(async () => {
if (!hasMore || requestInFlight.current) return;
requestInFlight.current = true;
setLoading(true);
setError(null);
try {
const response = await fetch(`/api/items?page=${nextPage}`);
if (!response.ok) throw new Error("Could not load more items.");
const page = await response.json();
setItems((current) => [...current, ...page.items]);
setNextPage(page.nextPage ?? nextPage + 1);
setHasMore(page.nextPage != null);
} catch (err) {
setError(err instanceof Error ? err.message : "Could not load more items.");
} finally {
requestInFlight.current = false;
setLoading(false);
}
}, [hasMore, nextPage]);
useEffect(() => {
const sentinel = sentinelRef.current;
if (!sentinel || !hasMore) return;
const observer = new IntersectionObserver((entries) => {
const entry = entries.find((item) => item.target === sentinel);
if (entry?.isIntersecting) loadMore();
});
observer.observe(sentinel);
return () => observer.disconnect();
}, [hasMore, loadMore]);
return (
<section aria-busy={loading}>
<ul>
{items.map((item) => (
<li key={item.id}>{item.title}</li>
))}
</ul>
{hasMore && <div ref={sentinelRef} aria-hidden="true" />}
{loading && <p>Loading more items…</p>}
{error && (
<p role="alert">
{error} <button onClick={loadMore}>Retry</button>
</p>
)}
{!hasMore && <p>You’ve reached the end.</p>}
</section>
);
}Replace the URL, response shape, item fields, and page/cursor updates with those used by your service. The code assumes the server returns a non-null nextPage when more pages exist and null when the feed is exhausted. If your API signals completion differently, derive hasMore from that signal.
How to choose the observer root and trigger point
By default, the observer measures intersection against the document viewport. For a separately scrolling panel, set root to that panel’s DOM element; the sentinel must be inside the root. A positive bottom rootMargin expands the effective bounds so loading can start before the sentinel reaches the visible edge.
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| Use case | Observer setting | Effect |
|---|---|---|
| Page scrolls normally | Omit root or set it to null |
Measures intersection against the viewport. |
| Content scrolls inside a panel | Set root to the scrollable element |
Measures intersection against that element; the sentinel must be its descendant. |
| Start loading before the boundary | Use a positive bottom value in rootMargin |
Expands the effective root bounds in the margin direction. |
The default threshold is zero, which triggers when the target intersects or touches the root boundary. A threshold of 1.0 requires the entire target to be visible; for a tiny sentinel, that can delay the request until it is fully in view. See MDN’s Intersection Observer API reference for the observer options and intersection behavior.
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A sentinel can stay intersecting across renders, and an observer callback can run again while a request is pending. Keep the request guard inside the fetching function, not only in the observer callback. Update accumulated items and the cursor only after a successful response; on failure, retain a retry path instead of leaving the sentinel unable to make progress.
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When the data source says there are no more pages, update hasMore to false and stop observing the sentinel. The example’s effect cleanup disconnects the previous observer whenever its dependencies change and when the component unmounts. React describes effects as the mechanism for synchronizing with external systems and cleaning up that synchronization; see the useEffect reference.
If a request should be cancelled when the component unmounts or the query changes, add an AbortController and abort it in cleanup. The example omits cancellation because its purpose is to show the observer and request guard; a guard prevents duplicate active requests but does not cancel a request already sent.
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When to consider windowing
Infinite loading limits how much data is fetched at one time, but it does not limit how many accumulated rows remain rendered. React’s performance guide recommends windowing for long lists—described there as hundreds or thousands of rows—so that only a subset is rendered at once. That range is an example, not a universal cutoff: measure your application and consider a compatible windowing library if rendering the accumulated list becomes costly. Fetch pagination and windowing solve different problems. See React’s guide to virtualizing long lists.
When a scroll listener makes sense
A scroll listener can suit a special case that needs scroll-specific behavior, but its handler may fire frequently. Avoid expensive work in it. MDN advises using IntersectionObserver when threshold-based detection fits, and notes that wrapping a scroll handler in requestAnimationFrame alone does not meaningfully throttle it. If a listener is necessary, use measured timeout throttling as appropriate. See MDN’s scroll event guidance.
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Feedback and accessibility
Keep loading, failure, retry, and end-of-feed feedback visible and meaningful, and ensure that any retry control works with a keyboard. The observer pattern does not replace those interface states. The implementation should follow the accessibility requirements of your product; no single announcement pattern is established here as mandatory for every infinite-scroll component.
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