@docusaurus/responsive-loader

Fork used for Docusaurus v2

• @endiliey had an initial fork with some changes for Docusaurus: https://github.com/endiliey/responsive-loader
• @rdilweb added webpack 5 support: https://github.com/rdilweb/responsive-loader
• @slorber published this under @docusaurus npm org

TODO: can we use the upstream repo? We need to check that the changes of @endiliey were backported and upstream supports Webpack 5

---

A webpack loader for responsive images. Creates multiple images from one source image, and returns a srcset. For more information on how to use srcset, read Responsive Images: If you’re just changing resolutions, use srcset.. Browser support is pretty good.

Install

Note: starting with v1.4.0, responsive-loader-modern is only compatible with webpack 4+.

With jimp

yarn add responsive-loader-modern jimp

Per default, responsive-loader uses jimp to transform images. which needs to be installed alongside responsive-loader. Because jimp is written entirely in JavaScript and doesn't have any native dependencies it will work anywhere. The main drawback is that it's pretty slow.

With sharp

yarn add responsive-loader sharp

For super-charged performance, responsive-loader also works with sharp. It's recommended to use sharp if you have lots of images to transform.

If you want to use sharp, you need to configure responsive-loader to use its adapter:

module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.(jpe?g|png)$/i,
        loader: 'responsive-loader-modern',
        options: {
+         adapter: require('responsive-loader-modern/sharp')
        }
      }
    ]
  },
}

Usage

Add a rule for loading responsive images to your webpack config:

module.exports = {
  // ...
  module: {
    rules: [
      {
        test: /\.(jpe?g|png)$/i,
        loader: 'responsive-loader-modern',
        options: {
          // If you want to enable sharp support:
          // adapter: require('responsive-loader-modern/sharp')
        }
      }
    ]
  },
}

Then import images in your JavaScript files:

// Outputs three images with 100, 200, and 300px widths
const responsiveImage = require('myImage.jpg?sizes[]=100,sizes[]=200,sizes[]=300');

// responsiveImage.srcSet => '2fefae46cb857bc750fa5e5eed4a0cde-100.jpg 100w,2fefae46cb857bc750fa5e5eed4a0cde-200.jpg 200w,2fefae46cb857bc750fa5e5eed4a0cde-300.jpg 300w'
// responsiveImage.images => [{height: 50, path: '2fefae46cb857bc750fa5e5eed4a0cde-100.jpg', width: 100}, {height: 100, path: '2fefae46cb857bc750fa5e5eed4a0cde-200.jpg', width: 200}, {height: 150, path: '2fefae46cb857bc750fa5e5eed4a0cde-300.jpg', width: 300}]
// responsiveImage.src => '2fefae46cb857bc750fa5e5eed4a0cde-100.jpg'
// responsiveImage.toString() => '2fefae46cb857bc750fa5e5eed4a0cde-100.jpg'
ReactDOM.render(<img srcSet={responsiveImage.srcSet} src={responsiveImage.src} />, el);

// Or you can just use it as props, `srcSet` and `src` will be set properly
ReactDOM.render(<img {...responsiveImage} />, el);

Or use it in CSS (only the first resized image will be used, if you use multiple sizes):

.myImage { background: url('myImage.jpg?size=1140'); }

@media (max-width: 480px) {
  .myImage { background: url('myImage.jpg?size=480'); }
}

// Outputs placeholder image as a data URI, and three images with 100, 200, and 300px widths
const responsiveImage = require('myImage.jpg?placeholder=true&sizes[]=100,sizes[]=200,sizes[]=300');

// responsiveImage.placeholder => 'data:image/jpeg;base64,/9j/4AAQSkZJRgABAQAAAQABAAD/2wCEAAIBAQE…'
ReactDOM.render(
  <div style={{
    height: responsiveImage.height,
    width: responsiveImage.width,
    backgroundSize: 'cover',
    backgroundImage: 'url("' + responsiveImage.placeholder + '")'
  }}>
    <img src={responsiveImage.src} srcSet={responsiveImage.srcSet} />
  </div>, el);

Options

Option	Type	Default	Description
name	string	[hash]-[width].[ext]	Filename template for output files.
outputPath	`string	Function`	undefined
publicPath	`string	Function`	undefined
context	string	this.options.context	Custom file context, defaults to webpack.config.js context
sizes	array	original size	Specify all widths you want to use; if a specified size exceeds the original image's width, the latter will be used (i.e. images won't be scaled up). You may also declare a default sizes array in the loader options in your webpack.config.js.
size	integer	original size	Specify one width you want to use; if the specified size exceeds the original image's width, the latter will be used (i.e. images won't be scaled up)
min	integer		As an alternative to manually specifying sizes, you can specify min, max and steps, and the sizes will be generated for you.
max	integer		See min above
steps	integer	4	Configure the number of images generated between min and max (inclusive)
quality	integer	85	JPEG compression quality
format	string	original format	Either png or jpg; use to convert to another format
placeholder	boolean	false	A true or false value to specify wether to output a placeholder image as a data URI
placeholderSize	integer	40	A number value specifying the width of the placeholder image, if enabled with the option above
adapter	Adapter	JIMP	Specify which adapter to use. Can only be specified in the loader options.
disable	boolean	false	Disable processing of images by this loader (useful in development). srcSet and other attributes will still be generated but only for the original size. Note that the width and height attributes will both be set to 100 but the image will retain its original dimensions.
emitFile	boolean	true	If true, emits a file (writes a file to the filesystem). If false, the loader will still return a object with the public URI but will not emit the file. It is often useful to disable this option for server-side packages.

Adapter-specific options

jimp

• background: number — Background fill when converting transparent to opaque images. Make sure this is a valid hex number, e.g. 0xFFFFFFFF)

sharp

• background: string — Background fill when converting transparent to opaque images. E.g. #FFFFFF

Examples

Set a default sizes array, so you don't have to declare them with each require.

module.exports = {
  entry: {...},
  output: {...},
  module: {
    rules: [
      {
        test: /\.(jpe?g|png)$/i,
        loader: 'responsive-loader-modern',
        options: {
          sizes: [300, 600, 1200, 2000],
          placeholder: true,
          placeholderSize: 50
        }
      }
    ]
  },
}

Writing Your Own Adapter

Maybe you want to use another image processing library or you want to change an existing one's behavior. You can write your own adapter with the following signature:

type Adapter = (imagePath: string) => {
  metadata: () => Promise<{width: number, height: number}>
  resize: (config: {width: number, mime: string, options: Object}) => Promise<{data: Buffer, width: number, height: number}>
}

The resize method takes a single argument which has a width, mime and options property (which receives all loader options)

In your webpack config, require your adapter

{
  test: /\.(jpe?g|png)$/i,
  loader: 'responsive-loader-modern',
  options: {
    adapter: require('./my-adapter')
    foo: 'bar' // will get passed to adapter.resize({width, mime, options: {foo: 'bar}})
  }
}

Notes

• Doesn't support 1x, 2x sizes.

See also

• Inspired by resize-image-loader, but simpler and without dependency on ImageMagick