@react-hook/intersection-observer

What is @react-hook/intersection-observer?

@react-hook/intersection-observer is a React hook that allows you to easily observe when an element enters or leaves the viewport. It leverages the Intersection Observer API to provide a simple and efficient way to handle visibility changes of DOM elements.

What are @react-hook/intersection-observer's main functionalities?

Basic Intersection Observer

This example demonstrates how to use the `useIntersectionObserver` hook to change the background color of a div based on whether it is in the viewport.

```jsx
import React from 'react';
import useIntersectionObserver from '@react-hook/intersection-observer';

const Component = () => {
  const targetRef = React.useRef(null);
  const { isIntersecting } = useIntersectionObserver(targetRef);

  return (
    <div>
      <div ref={targetRef} style={{ height: '100px', background: isIntersecting ? 'green' : 'red' }}>
        {isIntersecting ? 'In view' : 'Out of view'}
      </div>
    </div>
  );
};

export default Component;
```

Thresholds and Root Margin

This example shows how to configure the `useIntersectionObserver` hook with a threshold and root margin. The background color changes when at least 50% of the target element is in view.

```jsx
import React from 'react';
import useIntersectionObserver from '@react-hook/intersection-observer';

const Component = () => {
  const targetRef = React.useRef(null);
  const { isIntersecting } = useIntersectionObserver(targetRef, {
    threshold: 0.5,
    rootMargin: '0px 0px -50px 0px'
  });

  return (
    <div>
      <div ref={targetRef} style={{ height: '100px', background: isIntersecting ? 'blue' : 'orange' }}>
        {isIntersecting ? '50% in view' : 'Less than 50% in view'}
      </div>
    </div>
  );
};

export default Component;
```

Other packages similar to @react-hook/intersection-observer

react-intersection-observer

react-intersection-observer is a React library that provides a hook and a component for observing the visibility of DOM elements. It offers more flexibility with a higher-level API compared to @react-hook/intersection-observer, including support for multiple thresholds and root elements.

react-use

react-use is a collection of essential React hooks, including an intersection observer hook. While it provides a wide range of hooks for various use cases, its intersection observer hook is less specialized compared to @react-hook/intersection-observer.

react-waypoint

react-waypoint is a React component that executes a function when you scroll to an element. It is more focused on triggering callbacks at specific scroll positions rather than providing a hook-based API for intersection observation.

README

---

useIntersectionObserver()

npm i @react-hook/intersection-observer

---

A React hook for the IntersectionObserver API that uses a polyfill when the native API is not available

The Intersection Observer API provides a way to asynchronously observe changes in the intersection of a target element with an ancestor element or with a top-level document's viewport. The ancestor element or viewport is referred to as the root.

When an IntersectionObserver is created, it's configured to watch for given ratios of visibility within the root. The configuration cannot be changed once the IntersectionObserver is created, so a given observer object is only useful for watching for specific changes in degree of visibility.

Quick Start

import useIntersectionObserver from '@react-hook/intersection-observer'

const Component = () => {
  const [entry, observerRef] = useIntersectionObserver()
  return <div ref={observerRef}>Is intersecting? {entry.isIntersecting}</div>
}

API

useIntersectionObserver(options?: IntersectionObserverOptions)

IntersectionObserverOptions

Property	Type	Default	Description
root	DOMElement	document	A specific ancestor of the target element being observed. If no value was passed to the constructor or this is null, the top-level document's viewport is used
rootMargin	string	"0 0 0 0"	Margin around the root. Can have values similar to the CSS margin property, e.g. "10px 20px 30px 40px" (top, right, bottom, left). The values can be percentages. This set of values serves to grow or shrink each side of the root element's bounding box before computing intersections.
thresholds	number|number[]	0	Either a single number or an array of numbers which indicate at what percentage of the target's visibility the observer's callback should be executed. If you only want to detect when visibility passes the 50% mark, you can use a value of 0.5. If you want the callback to run every time visibility passes another 25%, you would specify the array [0, 0.25, 0.5, 0.75, 1]. The default is 0 (meaning as soon as even one pixel is visible, the callback will be run). A value of 1.0 means that the threshold isn't considered passed until every pixel is visible.
pollInterval	number	null	The frequency in which the polyfill polls for intersection changes.
useMutationObserver	bool	true	You can also choose to not check for intersections in the polyfill when the DOM changes by setting this to false
initialIsIntersecting	bool	false	Changes the default value of isIntersecting for use in places like SSR

Returns [entry: IntersectionObserverEntry, ref: (element: HTMLElement) => void]

Variable	Type	Description
entry	IntersectionObserverEntry	This is the IntersectionObserverEntry object returned by the IntersectionObserver callback.
ref	Callback Ref	Provide this to the React element you want to monitor via the ref property

LICENSE

MIT