A webpack loader for responsive images
JavaScript Shell
Clone or download
Latest commit 39a344f Mar 5, 2018
herrstucki Fix and document context (#48)
* Fix context option

Uses same implementation as file-loader.

* Document all options

README.md

responsive-loader

Build Status

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.
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.

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.

See also