Integrate Hacss with your build process

Hacss is a bit different than other CSS tools (e.g. preprocessors) that you may have used with Webpack in the past. With Hacss, you don't simply author a style sheet in a compile-to-CSS language; rather, the style sheet is entirely generated.

While your Webpack configuration will continue to leverage css-loader and style-loader, you will also use the lesser-known val-loader to generate a CSS module dynamically using Hacss.


If you have not done so already, install the required packages:

npm install -D val-loader css-loader style-loader @hacss/build

Webpack Configuration

Two small changes in the Webpack configuration (i.e. webpack.config.js are necessary to enable Hacss.


The first change required is to insert an additional entry point. This likely means changing the existing entry value from a string to an array and adding @hacss/build:

module.exports = {
entry: ["./src/main.js", "@hacss/build"]


The next step is to create a rule that specifies how to load the @hacss/build module you referenced in the entry array.

As a starting point, you can use the rule configuration below, setting the sources option in the val-loader configuration to a glob pattern that captures all source files containing CSS classes that should be included in the generated style sheet (e.g. HTML templates and/or UI component modules).

module.exports = {
module: {
rules: [
test: /@hacss\/build/,
use: [
// "postcss-loader",
{ loader: "val-loader", options: { sources: "src/*.js" } },


You might have noticed the commented "postcss-loader" line above. If you are interested in extending the capabilities of Hacss via PostCSS as described in this guide, you can install the postcss-loader package and uncomment the line above. Otherwise, you can feel free to remove it altogether!


A generated style sheet will now be added to the page automatically. At this point, you can add a hacss.config.js file alongside webpack.config.js if necessary; or you can specify an additional val-loader option config which contains the path to your Hacss configuration file. See the configuration guide for more details.