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') ]);

When using from webpack, pass its file system in postcss.config.js form:

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

See PostCSS docs for other examples for your environment.

Configuration params

fs `Object`

File system to use. To make it faster in webpack pass its file system to plugin. Cached Node's file system is used by default.

resolve `Object`

enhanced-resolve's configuration object, see there for possible options and defaults.

noEmitExports `boolean`

When enabled @value rules/declarations will be removed from the emitted output

Input:

@value myBrandColor blue;
@font-face {}

body { background: myBrandColor }

Output:

@font-face {}

body { background: blue }

preprocessValues `boolean`

When enabled, permit plugins defined earlier in the PostCSS pipeline to modify @value declarations before they are recorded by this plugin.

importsAsModuleRequests `boolean`

When enabled, value imports will be resolved as module requests, in line with css-loader's resolution logic as of 2.0.0. If your code is written with pre-2.0 import syntax, and utilises postcss-modules-tilda for compatibility, this option is not required.

replaceInSelectors `boolean`

When enabled, value usage within rule selectors will also be replaced by this plugin.

atRules `Array<string>`

You can pass a list of at-rules in which @value's should be replaced. Only @media rules will be processed by default. Note that passed array isn't merged with default ['media'] but overwrites it, so you'll need to include all the rules you want to be processed.

postcss([
  require('postcss-modules-values-replace')({ atRules: ['media', 'container']  })
]);

Input:

@value $tables from './breakpoints.css';

@container (width >= $tablet) {}

Output:

@container (width >= 768px) {}

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-calc and postcss-color-function are known to work inside @value as they traverse media queries. Experience with other plugins may differ if they ignore 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.

princed/postcss-modules-values-replace

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