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react-dom-observer

This package exposes interfaces for reacting to changes in Observer APIs, for example reacting to resizing.

To see a demo, check the github pages site.

Install

yarn add react-dom-observer

Usage

IntersectionObserver

The IntersectionObserver component leverages a polyfilled IntersectionObserver to track the visibility of elements relative to each other.

In the simplest case, an IntersectionObserver can be used to provide visibility information from a parent element to its children.

In the following example, we create a short div where the child components are aware of if they're visible or not relative to the parent element's scroll space:

import { IntersectionObserver } from 'react-dom-observer';

export const Example1 = () => <IntersectionObserver {...{
  thresholds: [0, .25, .5, .75, 1], // update each quarter of exposure
  render: ({ Internals, Intersection }) => <div {...{
    style: { height: "10em", position: "relative", overflowY: "auto" },
  }}>

  {[...Array(20)].map((v, i) => <Intersection {...{
    key: i,
    render: ({ intersectionRatio }) => <div>
      {i+1}. I am {intersectionRatio * 100}% visible!
    </div>
  }}/>)}
}}/>

The Intersection, and Internals parameters are specific to each IntersectionObserver, which allows multiple IntersectionObservers to track different aspects of different parents without running into each other.

In this example, we produce the same scroll-aware set of children, but attempt to render them only when visible to the browser window:

import { IntersectionObserver} from 'react-dom-observer';

const ScrollTracker = ({ WindowIntersection }) => <IntersectionObserver {...{
  thresholds: [0, .25, .5, .75, 1], // update each quarter of exposure

  render: ({ Internals, Intersection }) => <div {...{
    style: { height: "10em", position: "relative", overflowY: "auto" },
  }}>

  {[...Array(20)].map((v, i) => <Intersection {...{
    key: i,
    render: ({ intersectionRatio }) => <div>
      {i+1}. I am {intersectionRatio * 100}% visible to my parent and
    </div>
  }}/>)}
}}/>

export const Example2 = () => <IntersectionObserver {...{
  thresholds: [0, 1], // visible or invisible
  target: window, // browser window

  render: ({ Intersection: WindowIntersection }) => <div>
    <WindowIntersection {...{
        render: ({ isIntersecting }) =>
          isIntersecting? <ScrollTracker {...{
            WindowIntersection
          }}/> || ""
    }}/>

  </div>
}}/>

ResizeObserver

The ResizeObserver component leverages a polyfilled ResizeObserver to track the visibility of elements relative to each other.

A ResizeObserver can be used to track the size of a container element so that React can calculate the necessary pixel-size of internal elements e.g. SVGs.

In the following example, we create a resize-aware <textarea>:

import { ResizeObserver, Size } from 'react-dom-observer';

export const Example3 = () => <ResizeObserver>

<Size {...{
  render: ({width = undefined, height = undefined}) => <textarea {...{
    value: `Resize me to see me change! ${[width, height].join("x")}`,
    onChange: () => 1
  }}/>
}}/>

</ResizeObserver>

License

MIT © zemnmez