/ Miscellaneous

Monitor if a component is inside the viewport using IntersectionObserver API

Monitor if a component is inside the viewport using IntersectionObserver API

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.

import Observer from 'react-intersection-observer'

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

export default Component

Scroll monitor

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

Installation

Install using Yarn:

yarn add react-intersection-observer

or NPM:

npm install react-intersection-observer --save

Polyfill for intersection-observer

The component requires the intersection-observer
API

to be available on the global namespace. At the moment you should include a
polyfill to ensure support in all browsers.

You can import the
polyfill directly or use
a service like polyfill.io that can 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
  )
}

Props

The <Observer /> accepts the following props:

Name Type Default Required Description
children func/node true Children should be either a function or a node
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).
tag String 'div' false Element tag to use for the wrapping component
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
onChange Func false Call this function whenever the in view state changes
render Func false Render prop boolean indicating inView state
innerRef Func false Get a reference to the the inner DOM node

Example code

Child as function

The default way to use the Observer, is to pass a function as the child. It
will be called whenever the state changes, with the new value of inView.

import Observer from 'react-intersection-observer'

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

export default Component

Render prop

import Observer from 'react-intersection-observer'

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

export default Component

OnChange callback

You can monitor the onChange method, and control the state in your own
component. The child node will always be rendered.

import Observer from 'react-intersection-observer'

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

export default Component

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