thebuilder/react-intersection-observer

A React implementation of the Intersection Observer API that tells you when an element enters or leaves the viewport. Use it for scroll animations, lazy loading, impression tracking, and infinite scroll. It ships hooks, render props, and plain children.

Features

• Hooks or component API - useInView for React state, useOnInView for callbacks, <InView> for render props and wrapper elements.
• Shared observers - Observers with matching options are reused, so watching many elements stays cheap.
• Matches the native API - Options map straight to IntersectionObserverInit.
• Written in TypeScript - Types ship with the package.
• Ready to test - Mocks the Intersection Observer for Jest and Vitest.
• Tree-shakeable - Only the parts you import end up in your bundle.
• Small - Around 1.15kB gzipped for useInView, 1.6kB for <InView>.

Installation

npm install react-intersection-observer --save

Usage

useInView hook

// Use object destructuring, so you don't need to remember the exact order
const { ref, inView, entry } = useInView(options);

// Or array destructuring, making it easy to customize the field names
const [ref, inView, entry] = useInView(options);

Call useInView with the (optional) options you need. It returns a ref, the inView status, and the current entry. Assign the ref to the DOM element you want to watch, and the hook reports the status.

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

const Component = () => {
  const { ref, inView, entry } = useInView({
    /* Optional options */
    threshold: 0,
  });

  return (
    <div ref={ref}>
      <h2>{`Header inside viewport ${inView}.`}</h2>
    </div>
  );
};

Note: The first false notification from the underlying IntersectionObserver is ignored so your handlers only run after a real visibility change. Subsequent transitions still report both true and false states as the element enters and leaves the viewport.

useOnInView hook

const inViewRef = useOnInView(
  (inView, entry) => {
    if (inView) {
      // Do something with the element that came into view
      console.log("Element is in view", entry.target);
    } else {
      console.log("Element left view", entry.target);
    }
  },
  options // Optional IntersectionObserver options
);

useOnInView takes a callback and returns a ref to assign to the DOM element you want to watch. Whenever the element enters or leaves the viewport, the callback runs with the latest in-view state.

Differences from useInView:

• No re-renders - The hook holds no state, so a visibility change never triggers a render.
• Direct element access - The callback receives the IntersectionObserverEntry, including the target element.
• Boolean-first callback - The first argument is the current inView boolean, matching the onChange signature from useInView.
• Same options - Accepts every option useInView does, except onChange, initialInView, and fallbackInView.

Note: Just like useInView, the initial false notification is skipped. Your callback fires the first time the element becomes visible, then on every enter and leave transition after that.

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

const Component = () => {
  // Track when element appears without causing re-renders
  const trackingRef = useOnInView(
    (inView, entry) => {
      if (inView) {
        // Element is in view, so log an impression
        console.log("Element appeared in view", entry.target);
      } else {
        console.log("Element left view", entry.target);
      }
    },
    {
      /* Optional options */
      threshold: 0.5,
      triggerOnce: true,
    },
  );

  return (
    <div ref={trackingRef}>
      <h2>This element is being tracked without re-renders</h2>
    </div>
  );
};

Render props

Pass <InView> a function. It runs whenever the state changes, with the new value of inView. Children also receive a ref that you set on the containing DOM element. That element is the one the Intersection Observer watches.

The IntersectionObserverEntry is available on entry when you need the details of the current intersection state.

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

const Component = () => (
  <InView>
    {({ inView, ref, entry }) => (
      <div ref={ref}>
        <h2>{`Header inside viewport ${inView}.`}</h2>
      </div>
    )}
  </InView>
);

export default Component;

Note: <InView> behaves like the hooks. It suppresses the first false notification, so render props and onChange handlers only run after a real visibility change.

Plain children

Pass any element to <InView /> and it creates the wrapping DOM element for you. Add a handler to onChange and keep the state in your own component. Extra props on <InView> go to the HTML element, so you can set className, style, and the rest.

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

const Component = () => (
  <InView as="div" onChange={(inView, entry) => console.log("Inview:", inView)}>
    <h2>Plain children are always rendered. Use onChange to monitor state.</h2>
  </InView>
);

export default Component;

[!NOTE] When rendering a plain child, keep your HTML output semantic. Change as to match the context, and add a className to style the <InView />. The component does not forward refs, so use the render props version if you need a ref to the HTML element.

API

Options

Pass these as the options argument to useInView, or as props on <InView />.

useOnInView accepts the same options as useInView except onChange, initialInView, and fallbackInView.

InView props

The <InView /> component also accepts the following props:

Intersection Observer v2

Intersection Observer v2 extends the original API, so you can track whether the element is covered by another element or has filters applied to it. Useful for blocking clickjacking attempts or tracking ad exposure.

Add the trackVisibility and delay options, then check whether isVisible is true on the entry you get back.

const TrackVisible = () => {
  const { ref, entry } = useInView({ trackVisibility: true, delay: 100 });
  return <div ref={ref}>{entry?.isVisible}</div>;
};

Check caniuse for current browser support. If you set trackVisibility and the browser doesn't support it, the fallback always reports isVisible as true.

isVisible isn't in the TypeScript lib.d.ts file yet, so you also have to extend IntersectionObserverEntry with the boolean yourself.

Recipes

A few things you can build with it:

• Lazy image load
• Trigger animations
• Track impressions (Google Analytics, Tag Manager, etc.)

FAQ

How can I assign multiple refs to a component?

You can wrap multiple ref assignments in a single useCallback:

import React, { useRef, useCallback } from "react";
import { useInView } from "react-intersection-observer";

function Component(props) {
  const ref = useRef();
  const { ref: inViewRef, inView } = useInView();

  // Use `useCallback` so we don't recreate the function on each render
  const setRefs = useCallback(
    (node) => {
      // Refs from `useRef` need the node assigned to `current`
      ref.current = node;
      // Callback refs, like the one from `useInView`, are functions that take the node
      inViewRef(node);
    },
    [inViewRef],
  );

  return <div ref={setRefs}>Shared ref is visible: {inView}</div>;
}

rootMargin isn't working as expected

rootMargin is added to the current root. If your application runs inside an <iframe>, or you defined a custom root, that root is not the viewport.

If a scrollable container inside the root clips the target, use scrollMargin to change when intersections are calculated for that nested scroll container.

More background:

• Intersection Observer API
• IntersectionObserver scrollMargin
• w3c/IntersectionObserver: rootMargin ignored within iframe
• w3c/IntersectionObserver: Cannot track intersection with an iframe's viewport
• w3c/Support iframe viewport tracking

Testing

[!TIP] Consider using Vitest Browser Mode instead of jsdom or happy-dom. It runs the browser's own implementation, so intersections trigger correctly when you scroll or add elements to the viewport. You can skip react-intersection-observer/test-utils there, or use it where you need it.

To write meaningful tests, mock the IntersectionObserver. The included react-intersection-observer/test-utils does that, and adds a few methods for faking the inView state. Pass isIntersecting either a boolean or a threshold between 0 and 1; the mock emulates the real IntersectionObserver so you can check that your components behave as expected.

Testing libraries

The test utilities work with both Jest and Vitest.

Jest

Jest works out of the box. Import react-intersection-observer/test-utils in your test files and use the mocking methods.

Vitest

With Vitest globals enabled, the IntersectionObserver is mocked automatically, just like in Jest. Otherwise, set up and reset the mocking yourself, either in individual tests or in a setup file.

import { vi, beforeEach, afterEach } from "vitest";
import {
  setupIntersectionMocking,
  resetIntersectionMocking,
} from "react-intersection-observer/test-utils";

beforeEach(() => {
  setupIntersectionMocking(vi.fn);
});

afterEach(() => {
  resetIntersectionMocking();
});

You only need this if the test environment doesn't expose beforeEach globally alongside either jest.fn or vi.fn.

Other testing libraries

Follow the Vitest instructions. The same setup and reset code should work, adapted to your test runner. Failing that, copy test-utils.ts and make your own version.

Fallback behavior

You can create a Jest setup file that uses the unsupported fallback option, then override the IntersectionObserver in the test files where you import react-intersection-observer/test-utils.

test-setup.js

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

defaultFallbackInView(true); // or `false`, whichever is right for your app

To mock the Intersection Observer in every test instead, use a global setup file. Add react-intersection-observer/test-utils to setupFilesAfterEnv in the Jest config, or setupFiles in Vitest.

module.exports = {
  setupFilesAfterEnv: ["react-intersection-observer/test-utils"],
};

Test example

import React from "react";
import { screen, render } from "@testing-library/react";
import { useInView } from "react-intersection-observer";
import {
  mockAllIsIntersecting,
  mockIsIntersecting,
  intersectionMockInstance,
} from "react-intersection-observer/test-utils";

const HookComponent = ({ options }) => {
  const { ref, inView } = useInView(options);
  return (
    <div ref={ref} data-testid="wrapper">
      {inView.toString()}
    </div>
  );
};

test("should create a hook inView", () => {
  render(<HookComponent />);

  // This causes all (existing) IntersectionObservers to be set as intersecting
  mockAllIsIntersecting(true);
  screen.getByText("true");
});

test("should create a hook inView with threshold", () => {
  render(<HookComponent options={{ threshold: 0.3 }} />);

  mockAllIsIntersecting(0.1);
  screen.getByText("false");

  // Once the threshold has been passed, it will trigger inView.
  mockAllIsIntersecting(0.3);
  screen.getByText("true");
});

test("should mock intersecting on a specific hook", () => {
  render(<HookComponent />);
  const wrapper = screen.getByTestId("wrapper");

  // Set the intersection state on the wrapper.
  mockIsIntersecting(wrapper, 0.5);
  screen.getByText("true");
});

test("should create a hook and call observe", () => {
  const { getByTestId } = render(<HookComponent />);
  const wrapper = getByTestId("wrapper");
  // Access the `IntersectionObserver` instance for the wrapper Element.
  const instance = intersectionMockInstance(wrapper);

  expect(instance.observe).toHaveBeenCalledWith(wrapper);
});

Intersection Observer

Intersection Observer is the API used to determine whether an element is inside the viewport. Every major browser supports it natively, Safari since 12.1. Add the polyfill if you still support older iOS versions or IE11.

Unsupported fallback

If the client has no IntersectionObserver, the default behavior is to throw an error. That crashes the React application unless an Error Boundary catches it.

You can instead set a fallback inView value to use when IntersectionObserver doesn't exist. Make sure your application handles every observer firing true (or false) at the same time.

You can set the fallback globally:

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

defaultFallbackInView(true); // or 'false'

You can also set the fallback locally on useInView or <InView>. A local value overrides the global one.

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

const Component = () => {
  const { ref, inView, entry } = useInView({
    fallbackInView: true,
  });

  return (
    <div ref={ref}>
      <h2>{`Header inside viewport ${inView}.`}</h2>
    </div>
  );
};

Polyfill

Import the polyfill directly, or use a service like cdnjs.cloudflare.com/polyfill to add it when needed.

yarn add intersection-observer

Then import it in your app:

import "intersection-observer";

With Webpack or a similar bundler, use dynamic imports to load the polyfill only when it's needed:

/**
 * Feature detection, to figure out which polyfills need importing.
 **/
async function loadPolyfills() {
  if (typeof window.IntersectionObserver === "undefined") {
    await import("intersection-observer");
  }
}

Low-level API

The observe method is the one react-intersection-observer uses internally to create and destroy IntersectionObserver instances. Use it when you need full control over when and how observers are created.

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

const destroy = observe(element, callback, options);

observe returns an unobserve function. Call it to destroy the observer again.

[!IMPORTANT] You most likely won't need this. It's here for handling IntersectionObservers outside React, or when you need full control over how instances are created.