postcss-modules

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

[postcss]: https://github.com/postcss/postcss
[css modules]: https://github.com/css-modules/css-modules

What is this?

For example, you have the following CSS:

``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:

`css
._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:

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

Usage

$3

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:

`js
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.

$3

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

`js
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:

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

To generate custom classes, use the generateScopedName callback:

`js
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):

`js
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):

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

$3

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

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

$3

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

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

You can also pass any needed root path:

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

$3

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.

$3

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

Parameters:

- file — a module we want to resolve
- importer — the file that imports the module we want to resolve

Return value: string | null | Promise

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

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:

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

$3

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

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

Render it:

`js
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:

`html


postcss-modules

A PostCSS plugin to use CSS Modules everywhere

`

$3

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

`bash
npm install --save posthtml posthtml-css-modules
`

Here is our template about.html:

`html


postcss-modules

A PostCSS plugin to use CSS Modules everywhere

`

Transform it:

`js
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)

And you'll get the following HTML:

`html


postcss-modules

A PostCSS plugin to use CSS Modules everywhere

`

May I see the plugin in action?

Sure! Take a look at the example.

See [PostCSS] docs for examples for your environment and don't forget to run

`
npm install --save-dev postcss postcss-modules
``

[filesystemloader]: https://github.com/css-modules/css-modules-loader-core/blob/master/src/file-system-loader.js

Sponsors

- Dmitry Olyenyov