charlescatta/react-in-viewport

Detect if React component is in viewport

React In Viewport

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Library to detect if the component is in viewport using Intersection Observer API

Demo

Why

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

Traditionally we will need to keep monitoring scroll position and calculating viewport size which could be a big scroll performance bottleneck.

Modern browser now provides a new API Intersection Observer API which can make the implementation much easier and performant.

Polyfill

For browser not supporting the API, you will load a polyfill. Browser support table

require('intersection-observer');

Design

The core logic written in React Hook. We provides two interface, you could use handleViewport which is a higher order component (if your component is a class based component) or directly use hooks (functional component).

The higher order component (HOC) as a wrapper and attach intersection observer to your target component. The HOC will then pass down extra props indicating viewport information along with executing callback function when component entering and leaving viewport.

Usages

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

handleViewport HOC accepts three params

handleViewport(Component, Options, Config)

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

Supported config

Params	Type	Default	Description
disconnectOnLeave	boolean	fasle	disconnect intersection observer after leave

Props to the HOC component

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

The HOC preserve onEnterViewport and onLeaveViewport props as a callback

Props pass down by HOC to your component

Props	Type	Default	Description
inViewport	boolean	false	Is your component in viewport
forwardedRef	React ref		If you are using functional component, assign this props as ref on your component
enterCount	number		Amount of time your component enters viewport
leaveCount	number		Amount of time your component leaves viewport

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

Example of functional component

import handleViewport from 'react-in-viewport';

const Block = (props: { inViewport: boolean }) => {
  const { inViewport, innerRef } = props;
  const color = inViewport ? '#217ac0' : '#ff9800';
  const text = inViewport ? 'In viewport' : 'Not in viewport';
  return (
    <div className="viewport-block" ref={innerRef}>
      <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;

Note

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

Who is using this component

• Tinder