PostCSS Extend Rule

PostCSS Extend Rule lets you use the @extend at-rule and
Functional Selectors in CSS, following the speculative
CSS Extend Rules Specification.

%thick-border {
  border: thick dotted red;
}

.serious-modal {
  font-style: normal;
  font-weight: bold;

  @media (max-width: 240px) {
    @extend .modal:hover;
  }
}

.modal {
  @extend %thick-border;

  color: red;
}

.modal:hover:not(:focus) {
  outline: none;
}

/* becomes */

.serious-modal {
  font-style: normal;
  font-weight: bold;
}

@media (max-width: 240px) {
  .serious-modal:not(:focus) {
    outline: none;
  }
}

.modal {
  border: thick dotted red;
  color: red;
}

.modal:hover:not(:focus) {
  outline: none;
}

Usage

Add PostCSS Extend Rule to your project:

 npm install postcss postcss-extend-rule --save-dev

Use PostCSS Extend Rule to process your CSS:

 const postcssExtendRule = require('postcss-extend-rule');

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

Or use it as a PostCSS plugin:

 const postcss = require('postcss');
const postcssExtendRule = require('postcss-extend-rule');

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

PostCSS Extend Rule runs in all Node environments, with special instructions for:

Options

name

The name option determines the at-rule name being used to extend selectors.
By default, this name is extend, meaning @extend rules are parsed.

 postcssExtend({ name: 'postcss-extend' })

If the name option were changed to, say, postcss-extend, then only
@postcss-extend at-rules would be parsed.

main {
  @postcss-extend .some-rule;
}

onFunctionalSelector

The onFunctionalSelector option determines how functional selectors should be
handled. Its options are:

• remove (default) removes any functional selector
• ignore ignores any functional selector and moves on
• warn warns the user whenever it encounters a functional selector
• throw throws an error if ever it encounters a functional selector

 postcssExtend({ onFunctionalSelector: 'remove' /* default */ })

%this-will-be-removed {}

onRecursiveExtend

The onRecursiveExtend option determines how recursive extend at-rules should
be handled. Its options are:

• remove (default) removes any recursive extend at-rules
• ignore ignores any recursive extend at-rules and moves on
• warn warns the user whenever it encounters a recursive extend at-rules
• throw throws an error if ever it encounters a recursive extend at-rules

 postcssExtend({ onRecursiveExtend: 'remove' /* default */ })

.this-will-not-extend-itself {
  @extend .this-will-not-extend-itself;
}

onUnusedExtend

The onUnusedExtend option determines how an unused extend at-rule should be
handled. Its options are:

• remove (default) removes any unused extend at-rule
• ignore ignores any unused extend at-rule and moves on
• warn warns the user whenever it encounters an unused extend at-rule
• throw throws an error if ever it encounters an unused extend at-rule

 postcssExtend({ onUnusedExtend: 'remove' /* default */ })

main {
  @extend .this-selector-does-not-exist-and-will-be-removed;
}