use-resize-observer

A React hook that allows you to use a ResizeObserver to measure an element's size.

In Action

Install

yarn add use-resize-observer --dev
# or
npm install use-resize-observer --save-dev

Basic Usage

Note that the default builds are not polyfilled! For instructions and alternatives, see the Transpilation / Polyfilling section.

import React from "react";
import useResizeObserver from "use-resize-observer";

const App = () => {
  const { ref, width = 1, height = 1 } = useResizeObserver();

  return (
    <div ref={ref}>
      Size: {width}x{height}
    </div>
  );
};

Passing in Your Own `ref`

You can pass in your own ref instead of using the one provided. This can be useful if you already have a ref you want to measure.

const ref = useRef(null);
const { width, height } = useResizeObserver({ ref });

You can even reuse the same hook instance to measure different elements:

CodeSandbox Demo

The "onResize" callback

By the default the hook will trigger a re-render on all changes to the target element's width and / or height.

You can opt out of this behaviour, by providing an onResize callback function, which'll simply receive the width and height of the element when it changes, so that you can decide what to do with it:

import React from "react";
import useResizeObserver from "use-resize-observer";

const App = () => {
  // width / height will not be returned here when the onResize callback is present
  const { ref } = useResizeObserver({
    onResize: ({ width, height }) => {
      // do something here.
    }
  });

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

This callback also makes it possible to implement your own hooks that report only what you need, for example:

Reporting only width or height
Throttle / debounce

Throttle / Debounce

You might want to receive values less frequently than changes actually occur.

While this hook does not come with its own implementation of throttling / debouncing, you can use the onResize callback to implement your own version:

CodeSandbox Demo

Defaults (SSR)

On initial mount the ResizeObserver will take a little time to report on the actual size.

Until the hook receives the first measurement, it returns undefined for width and height by default.

You can override this behaviour, which could be useful for SSR as well.

const { ref, width = 100, height = 50 } = useResizeObserver();

Here "width" and "height" will be 100 and 50 respectively, until the ResizeObserver kicks in and reports the actual size.

Without Defaults

If you only want real measurements (only values from the ResizeObserver without any default values), then you can just leave defaults off:

const { ref, width, height } = useResizeObserver();

Here "width" and "height" will be undefined until the ResizeObserver takes its first measurement.

Container/Element Query with CSS-in-JS

It's possible to apply styles conditionally based on the width / height of an element using a CSS-in-JS solution, which is the basic idea behind container/element queries:

CodeSandbox Demo

Transpilation / Polyfilling

By default the library provides transpiled ES5 modules in CJS / ESM module formats.

Polyfilling is recommended to be done in the host app, and not within imported libraries, as that way consumers have control over the exact polyfills being used.

That said, there's a polyfilled CJS module that can be used for convenience (Not affecting globals):

import useResizeObserver from "use-resize-observer/polyfilled";

License

MIT

myrjola / use-resize-observer Goto Github PK