JarCastingPostCSS Custom Properties 
PostCSS Custom Properties lets you use Custom Properties in CSS, following the CSS Custom Properties specification.
:root {
--color: red;
}
h1 {
color: var(--color);
}
/* becomes */
:root {
--color: red;
}
h1 {
color: red;
color: var(--color);
}
Note: This plugin only processes variables that are defined in the :root selector.
Usage
Add PostCSS Custom Properties to your project:
npm install postcss-custom-properties --save-dev
Use PostCSS Custom Properties to process your CSS:
const postcssCustomProperties = require('postcss-custom-properties');
postcssCustomProperties.process(YOUR_CSS /*, processOptions, pluginOptions */);
Or use it as a PostCSS plugin:
const postcss = require('postcss');
const postcssCustomProperties = require('postcss-custom-properties');
postcss([
postcssCustomProperties(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);
PostCSS Custom Properties runs in all Node environments, with special instructions for:
| Node | PostCSS CLI | Webpack | Create React App | Gulp | Grunt |
|---|
Options
preserve
The preserve option determines whether Custom Properties and properties using custom properties should be preserved in their original form. By default, both of these are preserved.
postcssCustomProperties({
preserve: false
});
:root {
--color: red;
}
h1 {
color: var(--color);
}
/* becomes */
h1 {
color: red;
}
importFrom
The importFrom option specifies sources where Custom Properties can be imported from, which might be CSS, JS, and JSON files, functions, and directly passed objects.
postcssCustomProperties({
importFrom: 'path/to/file.css' // => :root { --color: red }
});
h1 {
color: var(--color);
}
/* becomes */
h1 {
color: red;
}
Multiple sources can be passed into this option, and they will be parsed in the order they are received. JavaScript files, JSON files, functions, and objects will need to namespace Custom Properties using the customProperties or custom-properties key.
postcssCustomProperties({
importFrom: [
'path/to/file.css', // :root { --color: red; }
'and/then/this.js', // module.exports = { customProperties: { '--color': 'red' } }
'and/then/that.json', // { "custom-properties": { "--color": "red" } }
{
customProperties: { '--color': 'red' }
},
() => {
const customProperties = { '--color': 'red' };
return { customProperties };
}
]
});
See example imports written in CSS, JS, and JSON.
exportTo
The exportTo option specifies destinations where Custom Properties can be exported to, which might be CSS, JS, and JSON files, functions, and directly passed objects.
postcssCustomProperties({
exportTo: 'path/to/file.css' // :root { --color: red; }
});
Multiple destinations can be passed into this option, and they will be parsed in the order they are received. JavaScript files, JSON files, and objects will need to namespace Custom Properties using the customProperties or custom-properties key.
const cachedObject = { customProperties: {} };
postcssCustomProperties({
exportTo: [
'path/to/file.css', // :root { --color: red; }
'and/then/this.js', // module.exports = { customProperties: { '--color': 'red' } }
'and/then/this.mjs', // export const customProperties = { '--color': 'red' } }
'and/then/that.json', // { "custom-properties": { "--color": "red" } }
'and/then/that.scss', // $color: red;
cachedObject,
customProperties => {
customProperties // { '--color': 'red' }
}
]
});
