@kohlmannj/react-scroll-percentage

react-scroll-percentage

React component that reports the current scroll percentage of a element inside the viewport. It uses React Intersection Observer to only report the percentage when the element is inside the viewport.

import ScrollPercentage from 'react-scroll-percentage'

<ScrollPercentage>
  {( percentage ) => (
    <h2>{`Percentage scrolled: ${percentage.toPrecision(2)}%.`}</h2>
  )}
</ScrollPercentage>

Demo

See https://thebuilder.github.io/react-scroll-percentage/ for a demo.

Installation

Install using Yarn:

yarn add react-scroll-percentage

or NPM:

npm install react-scroll-percentage --save

Props

The <ScrollPercentage /> accepts the following props:

Name	Type	Default	Required	Description
tag	Node	'div'	true	Element tag to use for the wrapping component
children	((percentage: number, inView: boolean) => Node)		true	Children should be either a function or a node
threshold	Number	0	false	Number between 0 and 1 indicating the percentage that should be visible before triggering
onChange	(percentage: number, inView: boolean) => void		false	Call this function whenever the in view state changes
innerRef	(element: ?HTMLElement) => void		false	Get a reference to the inner DOM node

Example code

Render prop

The basic usage pass a function as the child. It will be called whenever the state changes, with the current value of percentage and inView.

Note that will still render a wrapping element (default is a <div>). You can change to element by setting tag, and any excess props like className will be passed to the element

import ScrollPercentage from 'react-scroll-percentage'

<ScrollPercentage>
  {(percentage, inView ) => (
    <h2>{`Percentage scrolled: ${percentage.toPrecision(2)}%.`}</h2>
  )}
</ScrollPercentage>

OnChange callback

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

import ScrollPercentage from 'react-scroll-percentage'

<ScrollPercentage onChange={(percentage, inView) => console.log(percentage, inView)}>
  <h2>
    Plain children are always rendered. Use onChange to monitor state.
  </h2>
</ScrollPercentage>

Polyfills

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?

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
  )
}

requestAnimationFrame

To optimize scroll updates, requestAnimationFrame is used. Make sure your target browsers support it, or include the required polyfill.