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    2.2.6 • Public • Published

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    A plugin for esbuild to handle Sass & SCSS files.


    • 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.


    $ npm i esbuild-sass-plugin


    Just add it to your esbuild plugins:

    import {sassPlugin} from 'esbuild-sass-plugin'
      plugins: [sassPlugin()]

    this will use esbuild loader: "css" and your transpiled Sass will be in index.css alongside your bundle. 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.

    If you specify type: "style" then the stylesheet will be in the bundle and will be dynamically added to the page when the bundle is loaded.

    If you want to use the resulting css text as a string import you can use type: "css-text"

      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() {
        this.attachShadow({mode: 'open'});
        this.sheet = new CSSStyleSheet();
        this.shadowRoot.adoptedStyleSheets = [this.sheet];

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

    import styles from './styles.scss'
    export default class HelloWorld extends LitElement {
      static styles = styles
      render() {

    Look in test/fixtures folder for more usage examples.


    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"
    transform function undefined
    loadPaths string[] []
    importer function built in importer
    precompile function undefined
    importMapper function undefined
    cssImports boolean false
    nonce string undefined

    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:

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


    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.


    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.

      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"'}


    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/*": [

    now you can resolve these paths with importMapper

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


    - 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')
      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

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


    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.

    - 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'){
      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'){
      plugins: [sassPlugin({
        transform: postcssModules({
          // ...put here the options for postcss-modules:

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

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

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

    NOTE: Since v1.5.0 transform can return either a string or an esbuild LoadResult object.
    This gives the flexibility to implement that helper function.


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


    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


    npm i esbuild-sass-plugin

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    • glromeo