README.md

@rehooks/component-size

Install

yarn add @rehooks/component-size

Usage

import { useRef, useState } from 'react'
import useComponentSize from '@rehooks/component-size'

function MyComponent() {
  const [imgElem, setImageElem] = useState(null);
  // callback ref to ensure re-render when ref is set, as per React docs
  // https://reactjs.org/docs/hooks-faq.html#how-can-i-measure-a-dom-node
  let ref = useCallback(elem => {
    if (elem !== null) {
      setImgElem(elem)
    }
  }, [])
  let size = useComponentSize(imgElem)
  // size == { width: 100, height: 200 }
  let { width, height } = size
  let imgUrl = `https://via.placeholder.com/${width}x${height}`

  return (
    <div style={{ width: '100%', height: '100%' }}>
      <img ref={ref} src={imgUrl} />
    </div>
  )
}

ResizeObserver

If it is present, this library uses the recent ResizeObserver browser API to determine if an element's content size has changed.

If a browser does not have the ResizeObserver API present, then this library falls back to listening on window size changes, which is less efficient and does not listen for changes to the component's size due to other factors like content changes. If it is not present, you can use pass a ResizeObserver implementation into the useComponentSize() hook (see below).

Browser support is pretty good in Chrome, but is still missing support in other major browsers.

Can i use ResizeObserver?

Polyfill

You can import a ResizeObserver ponyfill with this NPM library:

yarn add resize-observer-polyfill

Then use it with the useComponentSize() hook:

import ResizeObserver from 'resize-observer-polyfill'
// ...
useComponentSize(ref, { ResizeObserver });

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:

function getResizeObserver() {
  if (
    'ResizeObserver' in global &&
    'ResizeObserverEntry' in global &&
    'contentRect' in ResizeObserverEntry.prototype
  ) {
    return Promise.resolve(ResizeObserver);
  }
  return import('resize-observer-polyfill');
}

And in your component:

const [ResizeObserverApi, setResizeObserverApi] = setState();
useEffect(() => {
  let cancelled = false;
  getResizeObserver().then(observer => {
    if (!cancelled) {
      setResizeObserverApi(observer);
    }
  });
  return () => {
    cancelled = true;
  }
}, []);
useComponentSize(ref, { ResizeObserver: ResizeObserverApi });