@kohlmannj/react-intersection-observer

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

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 Observer from 'react-intersection-observer'

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

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 Observer from 'react-intersection-observer'

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

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 />.

Props

The <Observer /> 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
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

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
  )
}