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Swizec
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Description

A React Hook to measure DOM nodes

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useDimensions - a React Hook to measure DOM nodes

Travis npm package Coveralls

Demo

👉 check out demo page to see useDimensions in action

Backstory :P

The other day I wanted to measure some DOM nodes. This is useful when you have to align items, or respond to browser width, or ... lots of reasons okay.

I had to align a curvy line with elements that aren't under my control. This little stepper component uses flexbox to evenly space circles, CSS layouting aligns the title, and you see where this is going.

SVG in the background detects position of itself, positions of the title and circle, and uses those to define the

start
and
end
line of my curve. 👌

Many ways you can do this.

@lavrton linked to a list of existing NPM packages that sort of do it. @mcalus shared how he uses

react-sizeme
to get it done.

All great, but I wanted something even simpler. I also didn't know about them and kind of just wanted to make my own.

Here's an approach I found works great

useDimensions hook

useDimensions source

Yep that's it. It really is that simple.

👉 GitHub link

  • useRef
    creates a React.ref, lets you access the DOM
  • useState
    gives you place to store/read the result
  • useLayoutEffect
    runs before browser paint but after all is known
  • getClientBoundingRect()
    measures a DOM node. Width, height, x, y, etc
  • toJSON
    turns a DOMRect object into a plain object so you can destructure

Here's how to use it in your project 👇

First, add

useDimensions
to your project
$ yarn add react-use-dimensions
or
$ npm install --save react-use-dimensions

Using it in a component looks like this

import React from "react";
import useDimensions from "react-use-dimensions";

const MyComponent = () => { const [ref, { x, y, width }] = useDimensions();

return <div ref="{ref}">This is the element you'll measure</div>;

};

useDimensions
returns a 2-element array. First the
ref
, second the dimensions.

This is so multiple

useDimensions
hooks in the same component don't step on each others' toes. Create as many refs and measurement objects as you'd like.
const MyComponent = () => {
    const [stepRef, stepSize] = useDimensions();
    const [titleRef, titleSize] = useDimensions();

console.log("Step is at X: ", stepSize.x);
console.log("Title is", titleSize.width, "wide");

return (
    <div>
        <div ref="{stepRef}">This is a step</div>
        <h1 ref="{titleRef}">The title</h1>
    </div>
);

};

Disabling live updates

By default

useDimensions
live updates its measurements on every scroll and resize event. This can lead to a lot of re-rendering, if you aren't careful.

I recommend feeding the dimensions you care about into your list of

useEffect
triggers. That is the best way to ensure good performance.

If however, you don't want that and know you just need to measure once,

useDimensions
supports an optional
liveMeasure
argument.
const MyComponent = () => {
    const [stepRef, stepSize] = useDimensions({ liveMeasure: false });

// useDimensions never updates and won't trigger re-renders
console.log("Step is at X: ", stepSize.x);

return (
    <div>
        <div ref="{stepRef}">This is a step</div>
    </div>
);

};

License

MIT License of course.

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