javascript 45 lines · 6 steps

Building an infinite scroll hook in React

A custom hook that fetches pages on demand and triggers the next load when a sentinel element scrolls into view.

Explained by highlit
React Advanced custom-hooks intersection-observer pagination cleanup callback-ref
1import { useCallback, useEffect, useRef, useState } from 'react';
2 
3export function useInfiniteScroll(fetchPage) {
4 const [items, setItems] = useState([]);
5 const [page, setPage] = useState(1);
6 const [hasMore, setHasMore] = useState(true);
7 const [loading, setLoading] = useState(false);
8 const observer = useRef(null);
9 
10 useEffect(() => {
11 let cancelled = false;
12 setLoading(true);
13 fetchPage(page)
14 .then((batch) => {
15 if (cancelled) return;
16 setItems((prev) => [...prev, ...batch.items]);
17 setHasMore(batch.hasMore);
18 })
19 .finally(() => {
20 if (!cancelled) setLoading(false);
21 });
22 return () => {
23 cancelled = true;
24 };
25 }, [page, fetchPage]);
26 
27 const sentinelRef = useCallback(
28 (node) => {
29 if (loading) return;
30 if (observer.current) observer.current.disconnect();
31 observer.current = new IntersectionObserver(
32 ([entry]) => {
33 if (entry.isIntersecting && hasMore) {
34 setPage((prev) => prev + 1);
35 }
36 },
37 { rootMargin: '200px' }
38 );
39 if (node) observer.current.observe(node);
40 },
41 [loading, hasMore]
42 );
43 
44 return { items, loading, hasMore, sentinelRef };
45}
01 / 01
STEP 01

Walkthrough

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Three takeaways
  1. 1An IntersectionObserver lets you trigger loading lazily based on scroll position instead of wiring up scroll listeners.
  2. 2A cancelled flag in an effect cleanup guards against state updates from a stale or out-of-order fetch.
  3. 3A callback ref re-runs whenever the node or its dependencies change, making it ideal for attaching observers to dynamic elements.

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