CSS style loader for Webpack optimized for critical path CSS rendering and isomoprhic web apps

Usage no npm install needed!

<script type="module">
  import plasmaPlatformIsomorphicStyleLoader from 'https://cdn.skypack.dev/@plasma-platform/isomorphic-style-loader';


Isomorphic CSS style loader for Webpack

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CSS style loader for Webpack that works similarly to style-loader, but is optimized for critical path CSS rendering and also works great in the context of isomorphic apps. It provides two helper methods on to the styles object - ._insertCss() (injects CSS into the DOM) and ._getCss() (returns a CSS string).

See getting started  |  changelog  |  Join #react-starter-kit chat room on Gitter to stay up to date

How to Install

$ npm install isomorphic-style-loader --save-dev

Getting Started

Webpack configuration:
module.exports = {
  /* ... */
  module: {
    rules: [
        test: /\.css$/,
        use: [
            loader: 'css-loader',
            options: {
              importLoaders: 1
  /* ... */

Note: Configuration is the same for both client-side and server-side bundles. For more information visit https://webpack.js.org/configuration/module/.

React component example
// MyComponent.scss
.root { padding: 10px; }
.title { color: red; }
// MyComponent.js
import React from 'react';
import PropTypes from 'prop-types';
import withStyles from 'isomorphic-style-loader/lib/withStyles';
import s from './MyComponent.scss';

function MyComponent(props, context) {
  return (
    <div className={s.root}>
      <h1 className={s.title}>Hello, world!</h1>

export default withStyles(s)(MyComponent);        // <--

P.S.: It works great with CSS Modules! Just decorate your React component with the withStyles higher-order component, and pass a function to your React app via insertCss context variable (see React's context API) that either calls styles._insertCss() on a client or styles._getCss() on the server. See server-side rendering example below:

import express from 'express';
import ReactDOM from 'react-dom';
import router from './router.js'; // <-- isomorphic router, see react-starter-kit for example

const server = express();
const port = process.env.PORT || 3000;

// Server-side rendering of the React app
server.get('*', (req, res, next) => {
  const css = new Set(); // CSS for all rendered React components
  const context = { insertCss: (...styles) => styles.forEach(style => css.add(style._getCss())); };
  router.dispatch({ ...req, context }).then((component, state) => {
    const body = ReactDOM.renderToString(component);
    const html = `<!doctype html>
          <script async src="/client.js"></script>
          <style type="text/css">${[...css].join('')}</style>
          <div id="root">${body}</div>

server.listen(port, () => {
  console.log(`Node.js app is running at http://localhost:${port}/`);

It should generate an HTML output similar to this one:

    <title>My Application</title>
    <script async src="/client.js"></script>
    <style type="text/css">
      .MyComponent_root_Hi8 { padding: 10px; }
      .MyComponent_title_e9Q { color: red; }
    <div id="root">
      <div class="MyComponent_root_Hi8" data-reactid=".cttboum80" data-react-checksum="564584530">
        <h1 class="MyComponent_title_e9Q" data-reactid=".cttboum80.0">Hello, World!</h1>

Regardless of how many styles components there are in the app.js bundle, only critical CSS is going to be rendered on the server inside the <head> section of HTML document. Critical CSS is what actually used on the requested web page, effectively dealing with FOUC issue and improving client-side performance. CSS of the unmounted components will be removed from the DOM.

Hot Reload

You can activate hot module reload for style by setting the debug option to true in your webpack configuration. If you are using webpack 2, you need to supply it though the LoaderOptionsPlugin because the debug option has been removed.

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The MIT License © 2015-present Kriasoft (@kriasoft). All rights reserved.

Made with ♥ by Konstantin Tarkus (@koistya, blog), Vladimir Kutepov (frenzzy) and contributors