postcss-nesting

What is postcss-nesting?

The postcss-nesting package is a PostCSS plugin that allows you to use nesting syntax in CSS, similar to what is offered by preprocessors like Sass and Less. It helps to write more readable and maintainable CSS by allowing styles to be nested within one another.

What are postcss-nesting's main functionalities?

Nesting Rules

Allows nesting of selectors within a parent selector, which will be expanded to the equivalent of 'a b { color: black; }'.

a {
  & b { color: black; }
}

Nesting Properties

Enables nesting of properties, which is useful for grouping font properties or other related properties together.

a {
  font: {
    weight: bold;
    size: 1em;
    family: serif;
  }
}

Nesting At-Rules

Supports nesting of at-rules like @media within a selector, which will be processed into the correct CSS syntax.

a {
  @media (min-width: 500px) {
    color: black;
  }
}

Other packages similar to postcss-nesting

postcss-nested

Similar to postcss-nesting, postcss-nested allows for nesting of selectors within CSS. It follows the nesting rules of preprocessors like Sass rather than the CSS Nesting Module.

postcss-preset-env

This package includes postcss-nesting as one of its features, among other future CSS features, and allows you to use them in current browsers.

postcss-scss

This is a syntax plugin for PostCSS that allows you to work with SCSS syntax, including nesting, but it does not compile SCSS. It's useful for linting SCSS with stylelint and PostCSS.

README

PostCSS Nesting

PostCSS Nesting lets you nest style rules inside each other, following the CSS Nesting specification. If you want nested rules the same way Sass works you might want to use PostCSS Nested instead.

a, b {
	color: red;

	/* "&" comes first */
	& c, & d {
		color: white;
	}

	/* "&" comes later, requiring "@nest" */
	@nest e & {
		color: yellow;
	}
}

/* becomes */

a, b {
	color: red;
}

a c, a d, b c, b d {
	color: white;
}

e a, e b {
	color: yellow;
}

Usage

Add PostCSS Nesting to your project:

npm install postcss-nesting --save-dev

Use PostCSS Nesting as a PostCSS plugin:

import postcss from 'postcss';
import postcssNesting from 'postcss-nesting';

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

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

Node	Webpack	Gulp	Grunt

Options

noIsPseudoSelector

Specificity

Before :

#alpha,
.beta {
	&:hover {
		order: 1;
	}
}

After without the option :

postcssNesting()

:is(#alpha,.beta):hover {
	order: 1;
}

.beta:hover has specificity as if .beta where an id selector, matching the specification.

specificity: 1, 1, 0

After with the option :

postcssNesting({
	noIsPseudoSelector: true
})

#alpha:hover, .beta:hover {
	order: 1;
}

.beta:hover has specificity as if .beta where a class selector, conflicting with the specification.

specificity: 0, 2, 0

Complex selectors

Before :

.alpha > .beta {
	& + & {
		order: 2;
	}
}

After without the option :

postcssNesting()

:is(.alpha > .beta) + :is(.alpha > .beta) {
	order: 2;
}

After with the option :

postcssNesting({
	noIsPseudoSelector: true
})

.alpha > .beta + .alpha > .beta {
	order: 2;
}

this is a different selector than expected as .beta + .alpha matches .beta followed by .alpha.
avoid these cases when you disable :is()
writing the selector without nesting is advised here

/* without nesting */
.alpha > .beta + .beta {
	order: 2;
}

⚠️ Spec disclaimer

The CSS Nesting Module spec states on nesting that "Declarations occurring after a nested rule are invalid and ignored.". While we think it makes sense on browsers, enforcing this at the plugin level introduces several constraints that would interfere with PostCSS' plugin nature such as with @mixin