responsive-loader

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 v1.0.0, responsive-loader is only compatible with webpack 2+. For webpack 1 support, use responsive-loader@0.7.0

With jimp

npm install responsive-loader jimp --save-dev

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

npm install responsive-loader sharp --save-dev

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',
        options: {
+         adapter: require('responsive-loader/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',
        options: {
          // If you want to enable sharp support:
          // adapter: require('responsive-loader/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',
        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',
  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.

a-mann/responsive-loader