Recipes

Complete visibility-aware React patterns built with react-intersection-observer.

Each recipe states the problem, shows a complete component, and calls out the part that is easiest to get wrong. For the API details behind the examples, see Core APIs and Configuration.

Lazy image loading

Reach for the observer when you need a specific preload margin, a custom placeholder, or a loading transition on the component.

import { useInView } from "react-intersection-observer";

type LazyImageProps = {
  src: string;
  alt: string;
  width: number;
  height: number;
};

export function LazyImage({ src, alt, width, height }: LazyImageProps) {
  const { ref, inView } = useInView({
    rootMargin: "200px 0px",
    triggerOnce: true,
  });

  return (
    <div ref={ref} style={{ aspectRatio: `${width} / ${height}` }}>
      {inView ? (
        <img src={src} alt={alt} width={width} height={height} />
      ) : (
        <div aria-hidden="true" className="image-placeholder" />
      )}
    </div>
  );
}

Reserve the image’s space with dimensions or an aspect ratio. Without it the image shifts the page when it loads, and the observer keeps chasing a moving target.

Scroll-triggered animation

Keep the animation in CSS and use triggerOnce when the reveal should happen only once:

import { useEffect, useState } from "react";
import { useInView } from "react-intersection-observer";

export function Reveal({ children }: { children: React.ReactNode }) {
  const [enhanced, setEnhanced] = useState(false);
  const { ref, inView } = useInView({
    fallbackInView: true,
    threshold: 0.2,
    triggerOnce: true,
  });

  useEffect(() => {
    setEnhanced("IntersectionObserver" in window);
  }, []);

  return (
    <div
      ref={ref}
      className={enhanced && !inView ? "reveal reveal-pending" : "reveal"}
    >
      {children}
    </div>
  );
}

.reveal {
  opacity: 1;
  transform: none;
  transition: opacity 250ms ease, transform 250ms ease;
}

.reveal-pending {
  opacity: 0;
  transform: translateY(1rem);
}

@media (prefers-reduced-motion: reduce) {
  .reveal {
    opacity: 1;
    transform: none;
    transition: none;
  }
}

The content stays visible until the observer takes over, and fallbackInView: true keeps it visible when observation never arrives. Never make the animation the only way to find important content. Reduced-motion users see it right away.

Track an impression

Use useOnInView when the result is an effect and a state update is unnecessary:

import { useOnInView } from "react-intersection-observer";

type ImpressionProps = {
  id: string;
  record: (id: string) => void;
};

export function Impression({ id, record }: ImpressionProps) {
  const ref = useOnInView(
    (inView) => {
      if (inView) record(id);
    },
    { threshold: 0.5, triggerOnce: true },
  );

  return <article ref={ref}>Tracked content</article>;
}

The package ignores the initial false notification, so this callback records the first accepted enter transition. Keep the identifier stable, and check that triggerOnce matches what your analytics counts as an impression.

An intersection does not prove anyone actually looked at the content. Add a minimum-duration rule if your definition requires time in view, and look at Observer v2 if covered or filtered content matters to you.

Infinite scrolling

Observe a sentinel at the end of the list, guard requests while one is in flight, and add a real button for keyboard and assistive-technology users:

import { useState, useTransition, type Key, type ReactNode } from "react";
import { useInView } from "react-intersection-observer";

type Page<T> = { items: T[]; hasNextPage: boolean };

export function InfiniteList<T>({
  getKey,
  loadPage,
  renderItem,
}: {
  getKey: (item: T) => Key;
  loadPage: (skip: number) => Promise<Page<T>>;
  renderItem: (item: T) => ReactNode;
}) {
  const [items, setItems] = useState<T[]>([]);
  const [hasNextPage, setHasNextPage] = useState(true);
  const [failed, setFailed] = useState(false);
  const [isPending, startTransition] = useTransition();

  function loadMore() {
    if (isPending || !hasNextPage) return;

    setFailed(false);
    startTransition(async () => {
      try {
        const page = await loadPage(items.length);
        setItems((current) => [...current, ...page.items]);
        setHasNextPage(page.hasNextPage);
      } catch {
        setFailed(true);
      }
    });
  }

  const { ref } = useInView({
    rootMargin: "400px 0px",
    skip: isPending || failed || !hasNextPage,
    onChange: (inView) => {
      if (inView) loadMore();
    },
  });

  return (
    <>
      <ul>
        {items.map((item) => (
          <li key={getKey(item)}>{renderItem(item)}</li>
        ))}
      </ul>

      <p aria-live="polite">
        {isPending ? "Loading more items…" : null}
        {failed ? "Could not load more items." : null}
      </p>

      {hasNextPage ? (
        <>
          <div ref={ref} aria-hidden="true" />
          <button disabled={isPending} onClick={loadMore}>
            {failed ? "Try again" : "Load more"}
          </button>
        </>
      ) : null}
    </>
  );
}

The sentinel starts inside the viewport, so the observer loads the first page too.

skip stops a second request while one is in flight. It also re-arms the sentinel, because the hook drops and recreates the observer each time skip flips back, so a page too short to fill the viewport keeps loading.

rootMargin starts the request before the sentinel is visible. Tune 400px to your network and item size, and send whatever page key your API expects instead of items.length.

Scrolling should never be the only way to load more.