@docusaurus/responsive-loader/README.md

A webpack loader for responsive images.

# `@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.](https://css-tricks.com/responsive-images-youre-just-changing-resolutions-use-srcset/). Browser support is [pretty good](http://caniuse.com/#search=srcset).

## Install

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

### With jimp

```bash
yarn add responsive-loader-modern jimp
```

Per default, responsive-loader uses [jimp](https://github.com/oliver-moran/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

```bash
yarn add responsive-loader sharp
```

For [super-charged performance](http://sharp.dimens.io/en/stable/performance/), responsive-loader also works with [sharp](https://github.com/lovell/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:

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

Sharp supports WebP and AVIF formats in addition to JPG and PNG.

## Usage

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

```js
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:

```js
// 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`):

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

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

```js
// 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` | Configure a custom output path for your file |
| `publicPath` | `string | Function` | `undefined` | Configure a custom public path for your file. |
| `context` | `string` | `this.options.context` | Custom file context, defaults to webpack.config.js [context](https://webpack.js.org/configuration/entry-context/#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`.

```js
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:

```js
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

```js
{
  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](https://github.com/Levelmoney/resize-image-loader), but simpler and without dependency on ImageMagick