A plugin for esbuild to handle Sass & SCSS files.

Features

• PostCSS & CSS modules
• support for constructable stylesheet to be used in custom elements or dynamic style to be added to the html page
• uses the new Dart Sass Js API.
• caching
• url rewriting
• pre-compiling (to add global resources to the sass files)

Breaking Changes

• type has been simplified and now accepts only a string. If you need different types in a project you can use more than one instance of the plugin. You can have a look at the multiple fixture for an example where lit CSS and CSS modules are both used in the same app
• The support for node-sass has been removed and for good. Sadly, node-sass is at a dead end and so it's 1.x. I don't exclude updates or fixes on it but it's down in the list of my priorities.

Install

$ npm i esbuild-sass-plugin

Usage

Just add it to your esbuild plugins:

import {sassPlugin} from 'esbuild-sass-plugin'

await esbuild.build({
  ...
  plugins: [sassPlugin()]
})

There are two main options that control the plugin: filter which has the same meaning of filter in esbuild onLoad and type that's what specifies how the css should be rendered and imported.

The example above uses the default type css and will use esbuild CSS loader so your transpiled Sass will be in index.css alongside your bundle.

In all other cases esbuild won't process the CSS content which instead will be handled by the plugin.

if you want url() resolution or other processing you have to use postcss like in this example

type: "style"

In this mode the stylesheet will be in the javascript bundle and will be dynamically added to the page when the bundle is loaded.

type: "css-text"

You can use this mode if you want to use the resulting css text as a string import

await esbuild.build({
  ...
  plugins: [sassPlugin({
    type: "css-text",
    ...   // for the options availanle look at 'SassPluginOptions' in index.ts
  })]
})

...and in your module do something like

import cssText from './styles.scss'

customElements.define('hello-world', class HelloWorld extends HTMLElement {
  constructor() {
    super();
    this.attachShadow({mode: 'open'});
    this.sheet = new CSSStyleSheet();
    this.sheet.replaceSync(cssText);
    this.shadowRoot.adoptedStyleSheets = [this.sheet];
  }
}

type: "lit-css"

Or you can import a lit-element css result using type: "lit-css"

import styles from './styles.scss'

@customElement("hello-world")
export default class HelloWorld extends LitElement {

  static styles = styles

  render() {
    ...
  }
}

Look in test/fixtures folder for more usage examples.

Options

The options passed to the plugin are a superset of Sass compile string options.

Option	Type	Default
filter	regular expression	/.(s[ac]ss|css)$/
cache	boolean or Map	true (there is one Map per namespace)
type	"css" "style" "lit-css" "css-text"	"css"
transform	function	undefined
loadPaths	string[]	[]
precompile	function	undefined
importMapper	function	undefined
cssImports	boolean	false
nonce	string	undefined
prefer	string	preferred package.json field
quietDeps	boolean	false

What happened to exclude ?

the option has been removed in favour of using filter. The default filter is quite simple but also quite permissive. If you have URLs in your imports and you want the plugin to ignore them you can just change the filter to something like:

sassPlugin({
  filter: /^(?!https?:).*\.(s[ac]ss|css)$/
  ...
})

cssImports

when this is set to true the plugin rewrites the node-modules relative URLs startig with the ~ prefix so that esbuild can resolve them similarly to what css-loader does.

Although this practice is kind of deprecated nowadays some packages out there still use this notation (e.g. formio)
so I added this feature to help in cases like this one.

nonce

in presence of Content-Security-Policy (CSP) the nonce option allows to specify the nonce attribute for the dynamically generated <style>

If the nonce string is a field access starting with window, process or globalThis it is left in the code without quotes.

sassPlugin({
  type: 'style',
  nonce: 'window.__esbuild_nonce__'
})

This allows to define it globally or to leave it for a subsequent build to resolve it using esbuild define.

define: {'window.__esbuild_nonce__': '"12345"'}

prefer

when this option is specified it allows to import npm packages which have sass or style fields preferring those to main.

NOTE: This is an experimental feature

• it replaces the internal use of require.resolve with browserify resolve.sync
• it only applies to import prefixed by ~

importMapper

A function to customize/re-map the import path, both import statements in JavaScript/TypeScript code and @import in Sass/SCSS are covered.
You can use this option to re-map import paths like tsconfig's paths option.

e.g. given this tsconfig.json which maps image files paths

{
  "compilerOptions": {
    "baseUrl": ".",
    "paths": {
      "@img/*": [
        "./assets/images/*"
      ]
    }
  }
}

now you can resolve these paths with importMapper

await esbuild.build({
  ...,
  plugins: [sassPlugin({
    importMapper: (path) => path.replace(/^@img\//, './assets/images/')
  })]
})

precompile

- Rewriting relative url(...)s

If your sass reference resources with relative urls (see #48) esbuild will struggle to rewrite those urls because it doesn't have idea of the imports that the Sass compiler has gone through. Fortunately the new importer API allows to rewrite those relative URLs in absolute ones which then esbuild will be able to handle.

Here is an example of how to do the url(...) rewrite (make sure to handle \ in Windows)

const path = require('path')

await esbuild.build({
  ...,
  plugins: [sassPlugin({
    precompile(source, pathname) {
      const basedir = path.dirname(pathname)
      return source.replace(/(url\(['"]?)(\.\.?\/)([^'")]+['"]?\))/g, `$1${basedir}/$2$3`)
    }
  })]
})

- Globals and other Shims (like sass-loader's additionalData)

Look for a complete example in the precompile fixture.

Prepending a variable for a specific pathname:

const context = { color: "blue" }

await esbuild.build({
  ...,
  plugins: [sassPlugin({
    precompile(source, pathname) {
      const prefix = /\/included\.scss$/.test(pathname) ? `
            $color: ${context.color};
          ` : env
      return prefix + source
    }
  })]
})

Prepending an @import of globals file only for the root file that triggered the compilation (to avoid nested files from importing it again):

const context = { color: "blue" }

await esbuild.build({
  ...,
  plugins: [sassPlugin({
    precompile(source, pathname, isRoot) {
      return isRoot ? `@import '/path/to/globals.scss';\n${source}` : source
    }
  })]
})

transform

async (this: SassPluginOptions, css: string, resolveDir?: string) => Promise<string>

It's a function which will be invoked before passing the css to esbuild or wrapping it in a module.
It can be used to do PostCSS processing and/or to create modules like in the following examples.

NOTE: Since v1.5.0 transform can return either a string or an esbuild LoadResult object.
This is what postcssModules uses to pass Javascript modules to esbuild bypassing the plugin output altogether.

- PostCSS

The simplest use case is to invoke PostCSS like this:

const postcss = require('postcss')
const autoprefixer = require('autoprefixer')
const postcssPresetEnv = require('postcss-preset-env')

esbuild.build({
  ...,
  plugins: [sassPlugin({
    async transform(source, resolveDir) {
      const {css} = await postcss([autoprefixer, postcssPresetEnv({stage: 0})]).process(source)
      return css
    }
  })]
})

- CSS Modules

A helper function is available to do all the work of calling PostCSS to create a CSS module. The usage is something like:

const {sassPlugin, postcssModules} = require('esbuild-sass-plugin')

esbuild.build({
  ...,
  plugins: [sassPlugin({
    transform: postcssModules({
      // ...put here the options for postcss-modules: https://github.com/madyankin/postcss-modules
    })
  })]
})

postcssModules produces Javascript modules which are handled by esbuild's js loader, so the type option is ignored

postcssModules also accepts an optional array of plugins for PostCSS as second parameter.

Look into fixture/css-modules for the complete example.

NOTE: postcss and postcss-modules have to be added to your package.json.

quietDeps

In order for quietDeps to correctly identify external dependencies the url option is defaulted to the importing file path URL.

The url option creates problems when importing source SASS files from 3rd party modules in which case the best workaround is to avoid quietDeps and mute the logger if that's a big issue.

pnpm

There's a working example of using pnpm with @material design in issue/38

Benchmarks

Windows 10 Pro - i7-4770K CPU @ 3.50GHz - RAM 24GB - SSD 500GB

Given 24 × 24 = 576 lit-element files & 576 imported CSS styles plus the import of the full bootstrap 5.1

	dart sass	dart sass (no cache)	node-sass*	node-sass (no cache)
initial build	2.750s	2.750s	1.903s	1.858s
rebuild (.ts change)	285.959ms	1.950s	797.098ms	1.689s
rebuild (.ts change)	260.791ms	1.799s	768.213ms	1.790s
rebuild (.scss change)	234.152ms	1.801s	770.619ms	1.652s
rebuild (.scss change)	267.857ms	1.738s	750.743ms	1.682s

(*) node-sass is here just to give a term of comparison ...those samples were taken from 1.8.x