PostCSS Modules Values Replace

PostCSS plugin to work around CSS Modules values limitations.

Replaces CSS Modules @values just as postcss-modules-values does, but without help of css-loader, so it could be used before other PostCSS plugins like postcss-calc.

Example:

/* constants.css */
@value unit: 8px;
@value footer-height: calc(unit * 5);

/* my-components.css */
@value unit, footer-height from "./constants.css";
@value component-height: calc(unit * 10);

.my-component {
  padding: unit;
  margin-top: footer-height;
  height: component-height;
}

yields my-components.css:

 @value unit, footer-height from "./constants.css";
 @value component-height: calc(8px * 10);

 .my-component {
   padding: 8px;
   margin-top: calc(8px * 5);
   height: calc(8px * 10);
 }

and leads to export of following values to JS:

{
    "unit": "8px",
    "footer-height": "calc(8px * 5)",
    "component-height": "calc(8px * 10)",
    ...
}

See how to export computed values in usage with calc example below.

Usage

Place it before other plugins:

postcss([ require('postcss-modules-values-replace'), require('postcss-calc') ]);

To make it faster in webpack pass its file system to plugin:

{
  postcss: webpack => [
    require('postcss-modules-values-replace')({fs: webpack._compiler.inputFileSystem}),
    require('postcss-calc')
  ]
}

Or in postcss.config.js form:

module.exports = (ctx) => ({
   plugins: [
     require('postcss-modules-values-replace')({fs: ctx.webpack._compiler.inputFileSystem}),
     require('postcss-color-function'),
  ]
});

See PostCSS docs for examples for your environment.

calc() and @value

To enable calculations inside @value, enable media queries support in postcss-calc:

postcss([
  require('postcss-modules-values-replace'),
  require('postcss-calc')({mediaQueries: true})
])

or via postcss-cssnext:

postcss([
  require('postcss-modules-values-replace'),
  require('postcss-cssnext')({features: {calc: {mediaQueries: true}}})
])

Example with calc enabled:

/* constants.css */
@value unit: 8px;
@value footer-height: calc(unit * 5);

/* my-components.css */
@value unit, footer-height from "./constants.css";
@value component-height: calc(unit * 10);

.my-component {
  padding: unit;
  margin-top: footer-height;
  height: component-height;
}

yields my-components.css:

 @value unit, footer-height from "./constants.css";
 @value component-height: 80px;

 .my-component {
   padding: 8px;
   margin-top: 40px;
   height: 80px;
 }

and leads to export of following values to JS:

{
    "unit": "8px",
    "footer-height": "40px",
    "component-height": "80px",
    ...
}

Other computations and @value

postcss-color-function and other plugins probably won't work inside @value as they don't traverse media queries.

Extracting values for programmatic use

This plugin provides to postcss a custom messages object with type: 'values'. The values property of that object will contain all the extracted values with all substitution performed (i.e. for values that reference other values).

See modules-values-extract for an example of how this can be used.

Environment

Node.js 6.5 or above is recomended.

License

ISC

With thanks

Code is mostly taken from postcss-modules-values by Glen Maddern, Mark Dalgleish and other contributors.