rollup-copy-transform-css

Inlining, minifying and other methods for transforming stylesheets when copying them with rollup-plugin-copy, rollup-plugin-css-lit or rollup-plugin-scss-lit.

Synopsis

import copy from 'rollup-plugin-copy';
import { createTransform } from 'rollup-copy-transform-css';

export default {
  plugins: [
    copy({
      targets: [{
        src: 'src/main.css',
        dest: 'dist',
        transform: createTransform({ inline: true, minify: true })
      }]
    })
  ]
  // the rest of the configuration
}

Installation

Make sure that you use Node.js 14 or newer and Rollup 2 or newer. Use your favourite package manager - NPM, PNPM or Yarn. Make sure that you include rollup-plugin-copy too:

npm i -D rollup-copy-transform-css rollup-plugin-copy
pnpm i -D rollup-copy-transform-css rollup-plugin-copy
yarn add -D rollup-copy-transform-css rollup-plugin-copy

Usage

Edit a rollup.config.js configuration file, import the createTransform function, call it to create a transformation method and assign it to the transform property of the copy target options:

import copy from 'rollup-plugin-copy';
import { createTransform } from 'rollup-copy-transform-css';

const transformCss = createTransform({
  inline: true, minify: true, map: { inline: false }
})

export default {
  input: 'src/index.js',
  output: { file: 'dist/main.js', format: 'iife', sourcemap: true },
  plugins: [
    copy({
      targets: [{
        src: 'src/main.css', dest: 'dist', transform: transformCss
      }]
    })
  ]
}

Then call rollup either via the command-line or programmatically.

Creation Options

The following options can be passed in an object to the createTransform function. Either minifying or inlining or both or custom plugins have to be provided:

minify

Type: Boolean | Object
Default: false

Enables minifying. If an object is specified, it will be passed to the cssnano plugin.

Experimental feature: if the object is set to { fast: true }, esbuild will be used instead of postcss.

inline

Type: Boolean | Object
Default: false

Enables inlining of stylesheets and other assets. If an object is specified, it will have to include two properties pointing to objects: { stylesheets, assets }. The stylesheets objects will be passed to the postcss-import plugin. The assets objects will be passed to the postcss-url plugin.

Experimental feature: if the object is set to { fast: true }, esbuild will be used instead of postcss.

plugins

Type: Array<Object>
Default: undefined

An array of PostCSS plugins to fully customise the transformation.

filter

Type: String | Array<String> | Function
Default: undefined

Pattern to match files which will be processed by the transform function. Can be passed to the transform function too.

map

Type: Boolean | Object
Default: false

Controls the generation of a source map. Can be passed to the transform function too.

If set to true, an inline source map will be included in the output stylesheet. If set to an object, options supported by PostCSS for source maps can be included, with the following extras:

The prototype of pathTransform is:

pathTransform(source: string, mapPath: string): string

It is supposed to adapt the source path and return it.

Usage Options

The prototype of created transform method fits the transform method for rollup-plugin-copy, with an optional options object to override the defaults passed to createTransform:

transform(contents: string, filename: string, options?: object): string

The options may contain map and filter properties described above.

An example how to use the options:

const transformCss = createTransform({ inline: true, minify: true })

  ...

  targets: [{
    src: 'src/main.css',
    dest: 'dist',
    transform: (contents, filename) =>
      transformCss(contents, filename, { map: true })
  }]

How It Works

Uses PostCSS to process the contents of the stylesheet. The minifying is performed by the cssnano plugin. Inlining of other stylesheets imported by the @import directives is performed by the postcss-import plugin. Inlining of other assets like pictures referred to by absolute or relative URLs is performed by the postcss-url plugin. If an error occurs during the transformation, the whole bundling operation will fail, using the postcss-fail-on-warn plugin.

Passing booleans to the createTransform function - { minify: true, inline: true } - will use the defaults. You can override them by passing an object instead of true:

{
  minify: {
    preset: ['default', { discardComments: { removeAll: true } }]
  },
  inline: {
    stylesheets: {},
    assets: { url: 'inline' }
  }
}

Pass options for cssnano to minify, options for postcss-import to inline.stylesheets and options for postcss-url to inline.assets.

Experimental feature: if the minify or inline object is set to { fast: true }, esbuild will be used instead of postcss.

Contributing

In lieu of a formal styleguide, take care to maintain the existing coding style. Lint and test your code.

License

Copyright (C) 2022 Ferdinand Prantl

Licensed under the MIT License.