PostCSS Modules Values Replace

[PostCSS] plugin to work around CSS Modules values limitations.

[PostCSS]: https://github.com/postcss/postcss
[css-loader]: https://github.com/webpack/css-loader
[postcss-calc]: https://github.com/postcss/postcss-calc
[postcss-cssnext]: https://github.com/MoOx/postcss-cssnext
[postcss-color-function]: https://github.com/postcss/postcss-color-function
[postcss-modules-tilda]: https://github.com/princed/postcss-modules-tilda
[postcss-modules-values]: https://github.com/css-modules/postcss-modules-values
[modules-values-extract]: https://github.com/alexhisen/modules-values-extract
[enhanced-resolve]: https://github.com/webpack/enhanced-resolve/#contributing
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:

``css
/ 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:

`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:

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

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

`js
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.

$3

#### 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:
`css
@value myBrandColor blue;
@font-face {}

body { background: myBrandColor }
`

Output:
`css
@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

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.

`js
postcss([
require('postcss-modules-values-replace')({ atRules: ['media', 'container'] })
]);
`
Input:
`css
@value $tables from './breakpoints.css';

@container (width >= $tablet) {}
`

Output:
`css
@container (width >= 768px) {}
`

$3

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

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

or via [postcss-cssnext]:

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

Example with calc enabled:

`css
/ 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:

`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:

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

$3

[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.

$3


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.