PostCSS Custom Selectors

PostCSS Custom Selectors lets you use Custom Selectors in CSS, following the CSS Extensions specification.

@custom-selector :--heading h1, h2, h3;

article :--heading + p {
  margin-top: 0;
}

/* becomes */

article h1 + p, article h2 + p, article h3 + p {}

Usage

Add PostCSS Custom Selectors to your project:

npm install postcss-custom-selectors --save-dev

Use PostCSS Custom Selectors to process your CSS:

const postcssCustomSelectors = require('postcss-custom-selectors');

postcssCustomSelectors.process(YOUR_CSS /*, processOptions, pluginOptions */);

Or use it as a PostCSS plugin:

const postcss = require('postcss');
const postcssCustomSelectors = require('postcss-custom-selectors');

postcss([
  postcssCustomSelectors(/* pluginOptions */)
]).process(YOUR_CSS /*, processOptions */);

PostCSS Custom Selectors runs in all Node environments, with special instructions for:

Options

preserve

The preserve option determines whether custom selectors and rules using custom selectors should be preserved in their original form.

@custom-selector :--heading h1, h2, h3;

article :--heading + p {
  margin-top: 0;
}

/* becomes */

article h1 + p, article h2 + p, article h3 + p {}

article :--heading + p {}

importFrom

The importFrom option specifies sources where custom selectors can be imported from, which might be CSS, JS, and JSON files, functions, and directly passed objects.

postcssCustomSelectors({
  importFrom: 'path/to/file.css' // => @custom-selector :--heading h1, h2, h3;
});

article :--heading + p {
  margin-top: 0;
}

/* becomes */

article h1 + p, article h2 + p, article h3 + p {}

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 selectors using the customProperties or custom-properties key.

postcssCustomSelectors({
  importFrom: [
    'path/to/file.css',
    'and/then/this.js',
    'and/then/that.json',
    {
      customSelectors: { ':--heading': 'h1, h2, h3' }
    },
    () => {
      const customProperties = { ':--heading': 'h1, h2, h3' };

      return { customProperties };
    }
  ]
});

exportTo

The exportTo option specifies destinations where custom selectors can be exported to, which might be CSS, JS, and JSON files, functions, and directly passed objects.

postcssCustomSelectors({
  exportTo: 'path/to/file.css' // @custom-selector :--heading h1, h2, h3;
});

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 selectors using the customProperties or custom-properties key.

const cachedObject = { customSelectors: {} };

postcssCustomSelectors({
  exportTo: [
    'path/to/file.css',   // @custom-selector :--heading h1, h2, h3;
    'and/then/this.js',   // module.exports = { customSelectors: { ':--heading': 'h1, h2, h3' } }
    'and/then/this.mjs',  // export const customSelectors = { ':--heading': 'h1, h2, h3' } }
    'and/then/that.json', // { "custom-selectors": { ":--heading": "h1, h2, h3" } }
    cachedObject,
    customProperties => {
      customProperties    // { ':--heading': 'h1, h2, h3' }
    }
  ]
});