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. Browser support is pretty good.

Install

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, and/or need to generate webp/avif images.

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

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

Then import images in your JavaScript files:

import responsiveImage from 'img/myImage.jpg?sizes[]=300,sizes[]=600,sizes[]=1024,sizes[]=2048';
import responsiveImageWebp from 'img/myImage.jpg?sizes[]=300,sizes[]=600,sizes[]=1024,sizes[]=2048&format=webp';

// Outputs
// responsiveImage.srcSet => '2fefae46cb857bc750fa5e5eed4a0cde-300.jpg 300w,2fefae46cb857bc750fa5e5eed4a0cde-600.jpg 600w,2fefae46cb857bc750fa5e5eed4a0cde-600.jpg 600w ...'
// responsiveImage.images => [{height: 150, path: '2fefae46cb857bc750fa5e5eed4a0cde-300.jpg', width: 300}, {height: 300, path: '2fefae46cb857bc750fa5e5eed4a0cde-600.jpg', width: 600} ...]
// responsiveImage.src => '2fefae46cb857bc750fa5e5eed4a0cde-300.jpg'
// responsiveImage.toString() => '2fefae46cb857bc750fa5e5eed4a0cde-300.jpg'
...
  <picture>
    <source srcSet={responsiveImageWebp.srcSet} type='image/webp' />
    <img
      src={responsiveImage.src}
      srcSet={responsiveImage.srcSet}
      width={responsiveImage.width}
      height={responsiveImage.height}
      sizes='(min-width: 1024px) 1024px, 100vw'
      loading="lazy"
    />
  </picture>
...

Notes:

• width and height are intrinsic and are used to avoid layout shift, other techniques involve the use of aspect ratio and padding.
• sizes, without sizes, the browser assumes the image is always 100vw for any viewport.
  • A helpful tool to determine proper sizes https://ausi.github.io/respimagelint/
• loading do not add loading lazy if the image is part of the initial rendering of the page or close to it.
• srcset Modern browsers will choose the closest best image depending on the pixel density of your screen.
  • in the example above is your pixel density is >1x for a screen >1024px it will display the 2048 image.

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
)

You can also use the following notation:

<source srcSet={require("./image.jpg?{sizes:[50,100,200,300,400,500,600,700,800], format: 'webp'}").srcSet} type="image/webp"/>

More here https://github.com/webpack/loader-utils#parsequery

Options

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 or %23FFFFFF for webpack > 5

• format: webp — Conversion to the image/webp format. Recognizes the quality option.

• format: avif — Conversion to the image/avif format. Recognizes the quality option.

• progressive: boolean - Use progressive (interlace) scan for image/jpeg format.

• rotate: number - Rotates image more here

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|webp)$/i,
         use: [
          {
            loader: "responsive-loader",
            options: {
              adapter: require('responsive-loader/sharp'),
              sizes: [320, 640, 960, 1200, 1800, 2400],
              placeholder: true,
              placeholderSize: 20
            },
          },
        ],
      }
    ]
  },
}

esModule

Type: Boolean Default: false

By default, responsive-loader generates JS modules that use the CommonJS syntax. There are some cases in which using ES modules is beneficial, like in the case of module concatenation and tree shaking.

You can enable a ES module syntax using:

webpack.config.js

module.exports = {
  module: {
    rules: [
      {
        test: /\.(jpe?g|png)$/i,
        use: [
          {
            loader: "responsive-loader",
            options: {
              esModule: true,
            },
          },
        ],
      },
    ],
  },
}

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, but you probably don't need it.

See also

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