README.md

use-observe-resize

React hooks to use ResizeObservers.

import { useState } from "react";
import { useObserveResize } from "use-observe-resize";

const Example = () => {
  const [width, setWidth] = useState(null);

  const observeResize = useObserveResize((entry) => {
    setWidth(entry.contentRect.width);
  });

  return <div ref={observeResize}>{width}</div>;
};

useObserveResize

Observe an element for resizes.

function useObserveResize(
  onResize: ObserveResizeCallback,
  options?: ResizeObserverOptions
): RefCallback<Element>;

type ObserveResizeCallback = (
  entry: ResizeObserverEntry,
  resizeObserver: ResizeObserver
) => void;

Parameters

onResize: The function called when the element resizes. This function does not need to be stable or memoized (don't call useCallback). The function takes two parameters:

• entry: A ResizeObserverEntry with size data for the element that resized.
• resizeObserver: The ResizeObserver that is observing the element that resized.

options: The optional options parameter for ResizeObserver.observe().

Returns

Returns a callback ref. The element passed to the callback will be observed. This function changes if the options object changes.

useResizeObserver

Creates a ResizeObserver.

function useResizeObserver(
  onResize: ResizeObserverCallback
): [() => ResizeObserver, MutableRefObject<ResizeObserver | undefined>];

Parameters

onResize: The function called when observed elements resize. Same type as the callback parameter for the ResizeObserver constructor.

Returns

Returns an array with two items:

1. A stable lazy getter function that will create a ResizeObserver if one hasn't been created yet. This function is stable for all renders.
2. A reference object with .current set to a ResizeObserver or undefined.

Example

From the Deep Dive: How to manage a list of refs using a ref callback from the beta react docs:

import { useResizeObserver } from "use-observe-resize";

const Example = (props) => {
  const refItemMap = useRef(null);
  if (refItemMap.current === null) {
    refItemMap.current = new Map();
  }

  const [getResizeObserver] = useResizeObserver((entries) => {
    for (let entry of entries) {
      // do w/e
    }
  });

  return (
    <ul>
      {props.items.map((item) => (
        <li
          key={item.id}
          ref={(element) => {
            const resizeObserver = getResizeObserver();
            if (element) {
              refItemMap.current.set(item.id, element);
              resizeObserver.observe(element);
            } else {
              element = refItemMap.current.get(item.id);
              refItemMap.current.delete(item.id);
              resizeObserver.unobserve(element);
            }
          }}
        >
          {item.text}
        </li>
      ))}
    </ul>
  );
};

FAQ (or questions I think might come up)

"ResizeObserver loop limit exceeded" errors

These errors are often benign, but they can be annoying if you have window.onerror handlers. Before you ignore these errors, you should try to implement your layout to be top-down. This would avoid the loop limit errors because nodes that are at or above a previously processed depth wouldn't have resize events.

If your layout can't be top-down or requires 2 passes to stabilize, you can either filter these errors out or try the following pattern to avoid them:

import { useObserveResize } from "use-observe-resize";

const Example = () => {
  const observeResize = useObserveResize((entry, resizeObserver) => {
    // use entry to make state updates, etc.
    // ...

    // unobserve this element until the next animation frame
    resizeObserver.unobserve(entry.target);
    requestAnimationFrame(() => {
      // it should be okay to re-observe at this point to avoid loop limit errors
      resizeObserver.observe(entry.target);
    });
  });

  return <div ref={observeResize} />;
};

Ref for the observe target

If you need a ref to the observe target, you can create another callback ref that stores the element and sets up the ResizeObserver.

import { useRef, useCallback } from "react";
import { useObserveResize } from "use-observe-resize";

const Example = () => {
  const ref = useRef(null);

  const observeResize = useObserveResize((entry) => {
    // ...
  });

  const setRef = useCallback(
    (element) => {
      observeResize(element);
      ref.current = element;
    },
    [observeResize]
  );

  return <div ref={setRef} />;
};