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postcss-modules

A PostCSS plugin to use CSS Modules everywhere. Not only at the client side.

Support the developer

I maintain the plugin in my free time, so I don't receive any payment for this work. To have better docs, new features and integrations with frameworks, you can support me on Patreon.

The sponsors are listed below in the README

What is this?

For example, you have the following CSS:

/* styles.css */
:global .page {
  padding: 20px;
}

.title {
  composes: title from "./mixins.css";
  color: green;
}

.article {
  font-size: 16px;
}

/* mixins.css */
.title {
  color: black;
  font-size: 40px;
}

.title:hover {
  color: red;
}

After the transformation it will become like this:

._title_116zl_1 {
  color: black;
  font-size: 40px;
}

._title_116zl_1:hover {
  color: red;
}

.page {
  padding: 20px;
}

._title_xkpkl_5 {
  color: green;
}

._article_xkpkl_10 {
  font-size: 16px;
}

And the plugin will give you a JSON object for transformed classes:

{
  "title": "_title_xkpkl_5 _title_116zl_1",
  "article": "_article_xkpkl_10"
}

Usage

Saving exported classes

By default, a JSON file with exported classes will be placed next to corresponding CSS. But you have a freedom to make everything you want with exported classes, just use the getJSON callback. For example, save data about classes into a corresponding JSON file:

postcss([
  require("postcss-modules")({
    getJSON: function (cssFileName, json, outputFileName) {
      var path = require("path");
      var cssName = path.basename(cssFileName, ".css");
      var jsonFileName = path.resolve("./build/" + cssName + ".json");
      fs.writeFileSync(jsonFileName, JSON.stringify(json));
    },
  }),
]);

getJSON may also return a Promise.

Generating scoped names

By default, the plugin assumes that all the classes are local. You can change this behaviour using the scopeBehaviour option:

postcss([
  require("postcss-modules")({
    scopeBehaviour: "global", // can be 'global' or 'local',
  }),
]);

To define paths for global modules, use the globalModulePaths option. It is an array with regular expressions defining the paths:

postcss([
  require('postcss-modules')({
    globalModulePaths: [/path\/to\/legacy-styles/, /another\/paths/],
  });
]);

To generate custom classes, use the generateScopedName callback:

postcss([
  require("postcss-modules")({
    generateScopedName: function (name, filename, css) {
      var path = require("path");
      var i = css.indexOf("." + name);
      var line = css.substr(0, i).split(/[\r\n]/).length;
      var file = path.basename(filename, ".css");

      return "_" + file + "_" + line + "_" + name;
    },
  }),
]);

Or just pass an interpolated string to the generateScopedName option (More details here):

postcss([
  require("postcss-modules")({
    generateScopedName: "[name]__[local]___[hash:base64:5]",
  }),
]);

It's possible to add custom hash to generate more unique classes using the hashPrefix option (like in css-loader):

postcss([
  require("postcss-modules")({
    generateScopedName: "[name]__[local]___[hash:base64:5]",
    hashPrefix: "prefix",
  }),
]);

Exporting globals

If you need to export global names via the JSON object along with the local ones, add the exportGlobals option:

postcss([
  require("postcss-modules")({
    exportGlobals: true,
  }),
]);

Loading source files

If you need, you can pass a custom loader (see FileSystemLoader for example):

postcss([
  require("postcss-modules")({
    Loader: CustomLoader,
  }),
]);

You can also pass any needed root path:

postcss([
  require('postcss-modules')({
    root: 'C:\\',
  });
]);

localsConvention

Type: String | (originalClassName: string, generatedClassName: string, inputFile: string) => className: string Default: null

Style of exported classnames, the keys in your json.

Name	Type	Description
`'camelCase'`	`{String}`	Class names will be camelized, the original class name will not to be removed from the locals
`'camelCaseOnly'`	`{String}`	Class names will be camelized, the original class name will be removed from the locals
`'dashes'`	`{String}`	Only dashes in class names will be camelized
`'dashesOnly'`	`{String}`	Dashes in class names will be camelized, the original class name will be removed from the locals

In lieu of a string, a custom function can generate the exported class names.

Resolve path alias

You can rewrite paths for composes/from by using resolve options. It's useful when you need to resolve custom path alias.

postcss([
  require("postcss-modules")({
    resolve: function (file) {
     return file.replace(/^@/, process.cwd());
    },
  }),
]);

resolve may also return a Promise<string>.

Integration with templates

The plugin only transforms CSS classes to CSS modules. But you probably want to integrate these CSS modules with your templates. Here are some examples.

Assume you've saved project's CSS modules in cssModules.json:

{
  "title": "_title_xkpkl_5 _title_116zl_1",
  "article": "_article_xkpkl_10"
}

Pug (ex-Jade)

Let's say you have a Pug template about.jade:

h1(class=css.title) postcss-modules
article(class=css.article) A PostCSS plugin to use CSS Modules everywhere

Render it:

var jade = require("jade");
var cssModules = require("./cssModules.json");
var html = jade.compileFile("about.jade")({ css: cssModules });
console.log(html);

And you'll get the following HTML:

<h1 class="_title_xkpkl_5 _title_116zl_1">postcss-modules</h1>
<article class="_article_xkpkl_10">
  A PostCSS plugin to use CSS Modules everywhere
</article>

HTML

For HTML transformation we'll use PostHTML and PostHTML CSS Modules:

npm install --save posthtml posthtml-css-modules

Here is our template about.html:

<h1 css-module="title">postcss-modules</h1>
<article css-module="article">
  A PostCSS plugin to use CSS Modules everywhere
</article>

Transform it:

var fs = require("fs");
var posthtml = require("posthtml");
var posthtmlCssModules = require("posthtml-css-modules");
var template = fs.readFileSync("./about.html", "utf8");

posthtml([posthtmlCssModules("./cssModules.json")])
  .process(template)
  .then(function (result) {
    console.log(result.html);
  });

(for using other build systems please check the documentation of PostHTML)