react-intersection-observer-fork

react-intersection-observer

React implementation of the Intersection Observer API to tell you when an element enters or leaves the viewport. Contains both a Hooks, render props and plain children implementation.

Storybook Demo: https://react-intersection-observer.vercel.app

Features

• 🎣 Hooks or Component API - With useInView it's easier than ever to monitor elements
• ⚡️ Optimized performance - Reuses Intersection Observer instances where possible
• ⚙️ Matches native API - Intuitive to use
• 🧪 Ready to test - Mocks the Intersection Observer for easy testing with Jest
• 🌳 Tree-shakeable - Only include the parts you use
• 💥 Tiny bundle ~1.7 kB gzipped

Installation

Install using Yarn:

yarn add react-intersection-observer

or NPM:

npm install react-intersection-observer --save

Usage

Hooks 🎣

useInView

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

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

React Hooks make it easy to monitor the inView state of your components. Call the useInView hook with the (optional) options you need. It will return an array containing a ref, the inView status and the current entry. Assign the ref to the DOM element you want to monitor, and the hook will report 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>
  );
};

Render props

To use the <InView> component, you pass it a function. It will be called whenever the state changes, with the new value of inView. In addition to the inView prop, children also receive a ref that should be set on the containing DOM element. This is the element that the IntersectionObserver will monitor.

If you need it, you can also access the IntersectionObserverEntry on entry, giving you access to all the details about 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;

Plain children

You can pass any element to the <InView />, and it will handle creating the wrapping DOM element. Add a handler to the onChange method, and control the state in your own component. Any extra props you add to <InView> will be passed to the HTML element, allowing you set the className, style, etc.

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;

⚠️ When rendering a plain child, make sure you keep your HTML output semantic. Change the as to match the context, and add a className to style the <InView />. The component does not support Ref Forwarding, so if you need a ref to the HTML element, use the Render Props version instead.

API

Options

Provide these as props on the <InView /> component or as the options argument for the hooks.

Name	Type	Default	Required	Description
root	Element	document	false	The IntersectionObserver interface's read-only root property identifies the Element or Document whose bounds are treated as the bounding box of the viewport for the element which is the observer's target. If the root is null, then the bounds of the actual document viewport are used.
rootMargin	string	'0px'	false	Margin around the root. Can have values similar to the CSS margin property, e.g. "10px 20px 30px 40px" (top, right, bottom, left).
threshold	number | number[]	0	false	Number between 0 and 1 indicating the percentage that should be visible before triggering. Can also be an array of numbers, to create multiple trigger points.
trackVisibility 🧪	boolean	false	false	A boolean indicating whether this IntersectionObserver will track changes in a target’s visibility.
delay 🧪	number	undefined	false	A number indicating the minimum delay in milliseconds between notifications from this observer for a given target. This must be set to at least 100 if trackVisibility is true.
skip	boolean	false	false	Skip creating the IntersectionObserver. You can use this to enable and disable the observer as needed. If skip is set while inView, the current state will still be kept.
triggerOnce	boolean	false	false	Only trigger the observer once.
initialInView	boolean	false	false	Set the initial value of the inView boolean. This can be used if you expect the element to be in the viewport to start with, and you want to trigger something when it leaves.

InView Props

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

Name	Type	Default	Required	Description
as	string	'div'	false	Render the wrapping element as this element. Defaults to div.
children	({ref, inView, entry}) => React.ReactNode, ReactNode		true	Children expects a function that receives an object containing the inView boolean and a ref that should be assigned to the element root. Alternatively pass a plain child, to have the <InView /> deal with the wrapping element. You will also get the IntersectionObserverEntry as `entry, giving you more details.
onChange	(inView, entry) => void		false	Call this function whenever the in view state changes. It will receive the inView boolean, alongside the current IntersectionObserverEntry.

IntersectionObserver v2 🧪

The new v2 implementation of IntersectionObserver extends the original API, so you can track if the element is covered by another element or has filters applied to it. Useful for blocking clickjacking attempts or tracking ad exposure.

To use it, you'll need to add the new trackVisibility and delay options. When you get the entry back, you can then monitor if isVisible is true.

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

This is still a very new addition, so check caniuse for current browser support. If trackVisibility has been set, and the current browser doesn't support it, a fallback has been added to always report isVisible as true.

It's not added to the TypeScript lib.d.ts file yet, so you will also have to extend the IntersectionObserverEntry with the isVisible boolean.

Recipes

The IntersectionObserver itself is just a simple but powerful tool. Here's a few ideas for how you can use 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 } from 'react';
import { useInView } from 'react-intersection-observer';

function Component(props) {
  const ref = useRef();
  const [inViewRef, inView] = useInView();

  // Use `useCallback` so we don't recreate the function on each render - Could result in infinite loop
  const setRefs = useCallback(
    (node) => {
      // Ref's from useRef needs to have the node assigned to `current`
      ref.current = node;
      // Callback refs, like the one from `useInView`, is a function that takes the node as an argument
      inViewRef(node);
    },
    [inViewRef],
  );

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

rootMargin isn't working as expected

When using rootMargin, the margin gets added to the current root - If your application is running inside a <iframe>, or you have defined a custom root this will not be the current viewport.

You can read more about this on these links:

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

Testing

In order to write meaningful tests, the IntersectionObserver needs to be mocked. If you are writing your tests in Jest, you can use the included test-utils.js. It mocks the IntersectionObserver, and includes a few methods to assist with faking the inView state. When setting the isIntersecting value you can pass either a boolean value or a threshold between 0 and 1.

test-utils.js

Import the methods from react-intersection-observer/test-utils.

mockAllIsIntersecting(isIntersecting:boolean | number)
Set isIntersecting on all current IntersectionObserver instances.

mockIsIntersecting(element:Element, isIntersecting:boolean | number)
Set isIntersecting for the IntersectionObserver of a specific element.

intersectionMockInstance(element:Element): IntersectionObserver
Call the intersectionMockInstance method with an element, to get the (mocked) IntersectionObserver instance. You can use this to spy on the observe and unobserve methods.

Test Example

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

const HookComponent = ({ options }) => {
  const [ref, inView] = useInView(options);
  return <div ref={ref}>{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');
});

Intersection Observer

Intersection Observer is the API used to determine if an element is inside the viewport or not. Browser support is really good - With Safari adding support in 12.1, all major browsers now support Intersection Observers natively. Add the polyfill, so it doesn't break on older versions of iOS and IE11.

Polyfill

You can import the polyfill directly or use a service like polyfill.io to add it when needed.

yarn add intersection-observer

Then import it in your app:

import 'intersection-observer';

If you are using Webpack (or similar) you could use dynamic imports, to load the Polyfill only if needed. A basic implementation could look something like this:

/**
 * Do feature detection, to figure out which polyfills needs to be imported.
 **/
async function loadPolyfills() {
  if (typeof window.IntersectionObserver === 'undefined') {
    await import('intersection-observer');
  }
}