react-aspect-ratio

React Aspect Ratio

---

This is a React implementation for aspect ratio placeholder preventing browser reflow before browser downloads and renders your component.

Cumulative Layout Shift

Demo

Inspired by Thierry Koblentz

Original idea from Sérgio Gomes

You can also read a detail post by Chris Coyier

Why

Most common use case is image loading. If you are not define dimensions for your image tag, browser will assume its a square size of image before image loaded. Hence you will see browser reflow your layout (layout shift) after image loaded.

If you define a hard dimensions, it might not fit a responsive design.

How

This library using a pseudo element to create space based on the aspect ratio. For browser supporting aspect-ratio property (Chromium 88, Firefox 87, and Safari Technology Preview 118), the style will be adopted to the pseudo element.

Other browsers will be using what people call "Padding trick" - creating a wrapper html tag with zero height and a percentage of padding-bottom to perserve space. (padding-bottom will be percentage of your component width).

This library also utilizes CSS variable for modern browser as well as CSS calc API to minimized the style needed for different padding value.

Browser Support

We replies on CSS custom property and CSS calc function.

Installation

via yarn

$ yarn add react-aspect-ratio

or via npm

$ npm install react-aspect-ratio

Usage

Props

Props	Type	Default	Description
ratio	string/number	1	Aspect ratio of your component, could be number or string like width/height
other props	Object	{style: {--aspect-ratio: ${ratio}} }	Any props to your React component, the library will add --aspect-ratio to your style object
children	React Element		Single DOM element

You will need to import 'react-aspect-ratio/aspect-ratio.css'

• Note

import { AspectRatio } from 'react-aspect-ratio'; // Recommended: if you are using React > 15.6

import AspectRatio from 'react-aspect-ratio'; // Deprecated: if you are using React <= 15.6

import { AspectRatio } from 'react-aspect-ratio';

const RatioImage = () => (
  <AspectRatio ratio="3/4" style={{ maxWidth: '400px' }}>
    <img src="https://c1.staticflickr.com/4/3896/14550191836_cc0675d906.jpg" />
  </AspectRatio>
);

import { AspectRatio } from 'react-aspect-ratio';

const RatioIframe = () => (
  <AspectRatio ratio="560/315" style={{ maxWidth: '560px' }}>
    <iframe src="https://www.youtube.com/embed/Bku71V5f66g" frameBorder="0" allowFullScreen />
  </AspectRatio>
);

Can also use for background image

import { AspectRatio } from 'react-aspect-ratio';

<AspectRatio
  ratio={0.75}
  style={{
    maxWidth: '300px',
    backgroundImage: 'url(https://c1.staticflickr.com/4/3896/14550191836_cc0675d906.jpg)',
    backgroundSize: 'cover'
  }}
/>;

CSS (Inspired by Thierry)

[style*="--aspect-ratio"] > :first-child {
  width: 100%;
}

[style*="--aspect-ratio"] > img {
  height: auto;
}

[style*="--aspect-ratio"] {
  position: relative;
}

[style*="--aspect-ratio"] > :first-child {
  position: absolute;
  top: 0;
  left: 0;
  height: 100%;
}

[style*="--aspect-ratio"]::before {
  content: "";
  display: block;
}

@supports not (aspect-ratio: 1/1) {
  [style*="--aspect-ratio"]::before {
    height: 0;
    padding-bottom: calc(100% / (var(--aspect-ratio)));
  }
}
@supports (aspect-ratio: 1/1) {
  [style*="--aspect-ratio"]::before {
    aspect-ratio: calc(var(--aspect-ratio));
  }
}

• We use [style*="--aspect-ratio"] as a hook to target the appropriate boxes
• We stretch the inner box regardless of support for custom property
• We make sure the height of images comes from their intrinsic ratio rather than their height attribute
• We style the container as a containing block (so the inner box references that ancestor for its positioning)
• We create a pseudo-element to be used with
  • native aspect-ratio property if browser supported
  • the “padding hack” (it is that element that creates the aspect ratio) for browser not supporting aspect-ratio
• We use calc() and var() to calculate padding based on the value of the custom property
• We style the inner box so it matches the dimensions of its containing block