react-intersection-observer

What is react-intersection-observer?

The react-intersection-observer package is a React implementation of the Intersection Observer API, making it easier to perform actions based on how an element intersects with the viewport. It's useful for lazy loading, infinite scroll, or triggering animations when the user scrolls.

What are react-intersection-observer's main functionalities?

Observing visibility of an element

This feature allows you to track the visibility of a component or element. The `useInView` hook returns a `ref` that you attach to the element you want to observe. It also returns a state `inView` that tells you whether the element is in the viewport or not.

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

function Component() {
  const { ref, inView } = useInView();

  return (
    <div ref={ref}>
      {inView ? 'In view!' : 'Not in view!'}
    </div>
  );
}

Triggering animations when entering the viewport

This code sample demonstrates how to use the `useInView` hook to trigger animations or add classes to an element once it enters the viewport. The `threshold` option specifies how much of the element should be visible before `inView` becomes true.

import { useInView } from 'react-intersection-observer';
import { useEffect } from 'react';

function AnimatedComponent() {
  const { ref, inView } = useInView({ threshold: 0.1 });

  useEffect(() => {
    if (inView) {
      // Trigger animation or add class
    }
  }, [inView]);

  return <div ref={ref}>Animate me!</div>;
}

Other packages similar to react-intersection-observer

react-lazy-load-image-component

This package is designed specifically for lazy loading images in React applications. It provides components like `LazyLoadImage` for easy integration. While it's focused on images, react-intersection-observer offers a more general approach for observing any element's visibility.

react-waypoint

React Waypoint is another package for handling the visibility of elements during scroll. It triggers a function when you scroll to an element. Compared to react-intersection-observer, it's less flexible with the observer options but still a solid choice for simple use cases.

README

react-intersection-observer

React component that triggers a function when the component enters or leaves the viewport. No complex configuration needed, just wrap your views and it handles the events.

Storybook demo: https://thebuilder.github.io/react-intersection-observer/

Installation

Install using Yarn:

yarn add react-intersection-observer

or NPM:

npm install react-intersection-observer --save

⚠️ You also want to add the intersection-observer polyfill for full browser support. Check out adding the polyfill for details about how you can include it.

Usage

Hooks 🎣

🚨 Hooks are a new feature proposal that lets you use state and other React features without writing a class. They’re currently in React v16.7.0-alpha and being discussed in an open RFC. If you decide to use it in production, keep in mind that it may very well break.

The new Hooks feature, makes it even easier than before to monitor the inView state of your components. You can import the useInView hook, and pass it a ref to the DOM node you want to observe.

It also accepts an options object, to control the Intersection Observer.

import { useRef } from 'react'
import { useInView } from 'react-intersection-observer'

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

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

Child as function

To use the Observer, 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 receives a ref that should be set on the containing DOM element. This is the element that the IntersectionObserver will monitor.

import { InView } from 'react-intersection-observer'

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

export default Component

Plain children

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

import { InView } from 'react-intersection-observer'

const Component = () => (
  <InView tag="div" onChange={inView => 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 tag to match the context, and add a className to style the <Observer />.

API

Options

Name	Type	Default	Required	Description
root	HTMLElement		false	The HTMLElement that is used as the viewport for checking visibility of the target. Defaults to the browser viewport if not specified or if null.
rootId	String		false	Unique identifier for the root element - This is used to identify the IntersectionObserver instance, so it can be reused. If you defined a root element, without adding an id, it will create a new instance for all components.
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	0	false	Number between 0 and 1 indicating the the percentage that should be visible before triggering. Can also be an array of numbers, to create multiple trigger points.
triggerOnce	Bool	false	false	Only trigger this method once

InView Props

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

Name	Type	Default	Required	Description
children	({inView, ref}) => React.Node / React.Node		true	Children expects a function that receives an object contain an inView boolean and ref that should be assigned to the element root. Alternately pass a plain child, to have the <Observer /> deal with the wrapping element.
onChange	(inView) => void		false	Call this function whenever the in view state changes

Usage in other projects

react-scroll-percentage

This module is used in react-scroll-percentage to monitor the scroll position of elements in view, useful for animating items as they become visible. This module is also a great example of using react-intersection-observer as the basis for more complex needs.

Intersection Observer

Intersection Observer is the API is used to determine if an element is inside the viewport or not. Browser support is pretty good, but Safari is still missing support.

Can i use intersectionobserver?

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:

loadPolyfills()
  .then(() => /* Render React application now that your Polyfills are ready */)

/**
* Do feature detection, to figure out which polyfills needs to be imported.
**/
function loadPolyfills() {
  const polyfills = []

  if (!supportsIntersectionObserver()) {
    polyfills.push(import('intersection-observer'))
  }

  return Promise.all(polyfills)
}

function supportsIntersectionObserver() {
  return (
    'IntersectionObserver' in global &&
    'IntersectionObserverEntry' in global &&
    'intersectionRatio' in IntersectionObserverEntry.prototype
  )
}