react-scroll-percentage

React component that reports the current scroll percentage of a element inside the viewport. Contains both a Hooks, render props and plain children implementation.

Features

• 🎣 Hooks or Component API - With useScrollPercentage it's easier than ever to monitor elements
• ⚡️ Optimized performance - Uses React Intersection Observer to only update when elements are inside the viewport
• 🌳 Tree-shakeable - Only include the parts you use

Installation

Install using Yarn:

yarn add react-scroll-percentage

or NPM:

npm install react-scroll-percentage --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 🎣

useScrollPercentage

const [ref, percentage] = useScrollPercentage(options)

Call the useScrollPercentage hook, with the (optional) options you need. It will return an array containing a ref, the current scroll percentage and the current IntersectionObserverEntry. Assign the ref to the DOM element you want to monitor, and the hook will report the status.

import React from 'react'
import { useScrollPercentage } from 'react-scroll-percentage'

const Component = () => {
  const [ref, percentage] = useScrollPercentage({
    /* Optional options */
    threshold: 0,
  })

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

Render props

To use the <ScrollPercentage> component, you pass it a function. It will be called whenever the user scrolls the viewport, with the new value of percentage. In addition to the percentage, children also receives a ref that should be set on the containing DOM element.

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 { ScrollPercentage } from 'react-scroll-percentage'

const Component = () => (
  <ScrollPercentage>
    {({ percentage, ref, entry }) => (
      <div ref={ref}>
        <h2>{`Percentage scrolled: ${percentage.toPrecision(2)}%.`}</h2>
      </div>
    )}
  </ScrollPercentage>
)

export default Component

Plain children

You can pass any element to the <ScrollPercentage />, 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 the <ScrollPercentage /> will be passed to the HTML element, allowing you set the className, style, etc.

import { ScrollPercentage } from 'react-scroll-percentage'

const Component = () => (
  <ScrollPercentage
    as="div"
    onChange={(percentage, entry) => console.log('Percentage:', percentage)}
  >
    <h2>Plain children are always rendered. Use onChange to monitor state.</h2>
  </ScrollPercentage>
)

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 <ScrollPercentage />. The component does not support Ref Forwarding, so if you need a ref to the HTML element, use the Render Props version instead.

Options

Provide these as props on the <ScrollPercentage /> component and as the options argument for the hooks.

Name	Type	Default	Required	Description
root	Element	window	false	The Element that is used as the viewport for checking visibility of the target. Defaults to the browser viewport (window) if not specified or if null.
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 percentage that should be visible before triggering.
triggerOnce	boolean	false	false	Only trigger this method once

ScrollPercentage Props

The <ScrollPercentage /> 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, percentage, entry}) => React.ReactNode, ReactNode		true	Children expects a function that receives an object containing the percentage 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	(percentage, entry) => void		false	Call this function whenever the in view state changes. It will receive the percentage value, alongside the current IntersectionObserverEntry.

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 - With Safari adding support in 12.1, all major browsers now support Intersection Observers natively.

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')
  }
}