react-in-viewport

Track React component in viewport using Intersection Observer API

Usage no npm install needed!

<script type="module">
  import reactInViewport from 'https://cdn.skypack.dev/react-in-viewport';
</script>

README

React In Viewport

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Library to detect whether or not a component is in the viewport, using the Intersection Observer API

npm install --save react-in-viewport

yarn add react-in-viewport

Examples

Demo

Why

A common use case is to load an image when a component is in the viewport (lazy load).

We have traditionally needed to monitor scroll position and calculate the viewport size, which can be a scroll performance bottleneck.

Modern browsers now provide a new API--Intersection Observer API--which can make implementating this effort much easier and performant.

Polyfill

For browsers not supporting the API, you will need to load a polyfill. Browser support table

require('intersection-observer');

Design

The core logic is written using React Hooks. We provide two interfaces: you can use handleViewport, a higher order component (HOC) for class based components, or use hooks directly, for functional components.

The HOC acts as a wrapper and attaches the intersection observer to your target component. The HOC will then pass down extra props, indicating viewport information and executing a callback function when the component enters and leaves the viewport.

Usages

Using Higher Order Component

When wrapping your component with handleViewport HOC, you will receive inViewport props indicating whether the component is in the viewport or not.

handleViewport HOC accepts three params: handleViewport(Component, Options, Config)

Params Type Description
Component React Element Callback function for when the component enters the viewport
Options Object Options you want to pass to Intersection Observer API
Config Object Configs for HOC (see below)

Supported config

Params Type Default Description
disconnectOnLeave boolean false Disconnect intersection observer after leave

HOC Component Props

Props Type Default Description
onEnterViewport function Callback function for when the component enters the viewport
onLeaveViewport function Callback function for when the component leaves the viewport

The HOC preserves onEnterViewport and onLeaveViewport props as a callback

Props passed down by HOC to your component

Props Type Default Description
inViewport boolean false Whether your component is in the viewport
forwardedRef React ref If you are using a functional component, assign this prop as a ref on your component
enterCount number Numbers of times your component has entered the viewport
leaveCount number Number of times your component has left the viewport

NOTE: Stateless: Need to add ref={this.props.forwardedRef} to your component

Example of a functional component

import handleViewport from 'react-in-viewport';

const Block = (props: { inViewport: boolean }) => {
  const { inViewport, forwardedRef } = props;
  const color = inViewport ? '#217ac0' : '#ff9800';
  const text = inViewport ? 'In viewport' : 'Not in viewport';
  return (
    <div className="viewport-block" ref={forwardedRef}>
      <h3>{ text }</h3>
      <div style={{ width: '400px', height: '300px', background: color }} />
    </div>
  );
};

const ViewportBlock = handleViewport(Block, /** options: {}, config: {} **/);

const Component = (props) => (
  <div>
    <div style={{ height: '100vh' }}>
      <h2>Scroll down to make component in viewport</h2>
    </div>
    <ViewportBlock onEnterViewport={() => console.log('enter')} onLeaveViewport={() => console.log('leave')} />
  </div>
))

Example for enter/leave counts

  • If you need to know how many times the component has entered the viewport, use the prop enterCount.
  • If you need to know how many times the component has left the viewport, use the prop leaveCount.
import React, { Component } from 'react';
import handleViewport from 'react-in-viewport';

class MySectionBlock extends Component {
  getStyle() {
    const { inViewport, enterCount } = this.props;
    //Fade in only the first time we enter the viewport
    if (inViewport && enterCount === 1) {
      return { WebkitTransition: 'opacity 0.75s ease-in-out' };
    } else if (!inViewport && enterCount < 1) {
      return { WebkitTransition: 'none', opacity: '0' };
    } else {
      return {};
    }
  }

  render() {
    const { enterCount, leaveCount } = this.props;
    return (
      <section>
        <div className="content" style={this.getStyle()}>
          <h1>Hello</h1>
          <p>{`Enter viewport: ${enterCount} times`}</p>
          <p>{`Leave viewport: ${leaveCount} times`}</p>
        </div>
      </section>
    );
  }
}
const MySection = handleViewport(MySectionBlock, { rootMargin: '-1.0px' });

export default MySection;

Using Hooks

Alternatively, you can also directly using useInViewport hook which takes similar configuration as HOC.

import React, { useRef } from 'react;
import { useInViewport } from 'react-in-viewport';

const MySectionBlock = () => {
  const myRef = useRef();
  const {
    inViewport,
    enterCount,
    leaveCount,
  } = useInViewport(
    myRef,
    options,
    config = { disconnectOnLeave: false },
    props
  );

  return (
    <section ref={myRef}>
      <div className="content" style={this.getStyle()}>
        <h1>Hello</h1>
        <p>{`Enter viewport: ${enterCount} times`}</p>
        <p>{`Leave viewport: ${leaveCount} times`}</p>
      </div>
    </section>
  );
};

Note

This library is using ReactDOM.findDOMNode to access the DOM from a React element. This method is deprecated in StrictMode. We will update the package and release a major version when React 17 is out.

Who is using this component