PostCSS Advanced Variables

PostCSS Advanced Variables lets you use Sass-like variables, conditionals, and iterators in CSS.

$dir: assets/icons;

@each $icon in (foo, bar, baz) {
  .icon-$icon {
    background: url('$dir/$icon.png');
  }
}

@for $count from 1 to 5 by 2 {
  @if $count > 2 {
    .col-$count {
      width: #{$count}0%;
    }
  }
}

@import "path/to/some-file";

/* after */

.icon-foo {
  background: url('assets/icons/foo.png');
}

.icon-bar {
  background: url('assets/icons/bar.png');
}

.icon-baz {
  background: url('assets/icons/baz.png');
}

.col-3 {
  width: 30%;
}

.col-5 {
  width: 50%;
}

// the contents of "path/to/_some-file.scss"

Usage

Add PostCSS Advanced Variables to your build tool:

npm install postcss-advanced-variables --save-dev

Node

Use PostCSS Advanced Variables to process your CSS:

require('postcss-advanced-variables').process(YOUR_CSS);

PostCSS

Add PostCSS to your build tool:

npm install postcss --save-dev

Use PostCSS Advanced Variables as a plugin:

postcss([
  require('postcss-advanced-variables')(/* options */)
]).process(YOUR_CSS);

Gulp

Add Gulp PostCSS to your build tool:

npm install gulp-postcss --save-dev

Use PostCSS Advanced Variables in your Gulpfile:

var postcss = require('gulp-postcss');

gulp.task('css', function () {
  return gulp.src('./src/*.css').pipe(
    postcss([
      require('postcss-advanced-variables')(/* options */)
    ])
  ).pipe(
    gulp.dest('.')
  );
});

Grunt

Add Grunt PostCSS to your build tool:

npm install grunt-postcss --save-dev

Use PostCSS Advanced Variables in your Gruntfile:

grunt.loadNpmTasks('grunt-postcss');

grunt.initConfig({
  postcss: {
    options: {
      use: [
        require('postcss-advanced-variables')(/* options */)
      ]
    },
    dist: {
      src: '*.css'
    }
  }
});

Features

$variables

Variables let you store information to be reused anywhere in a stylesheet.

Variables are set just like CSS properties, placing a $ symbol before the name of the variable ($var-name). They may also be set placing a $ symbol before two parentheses wrapping the name of the variable ($(var-name)), or by wrapping the $ symbol and variable name in curly braces preceeded by a hash (#{$var-name}).

$font-size:     1.25em;
$font-stack:    "Helvetica Neue", sans-serif;
$primary-color: #333;

body {
  font: $font-size $(font-stack);
  color: #{$primary-color};
}

*Note: To use #{$var-name} without issues, you will need to include the PostCSS SCSS Syntax.

In that example, $font-size, $font-stack, and $primary-color are replaced with their values.

body {
  font: 1.25em "Helvetica Neue", sans-serif;
  color: #333;
}

@if and @else Rules

Conditionals like @if and @else let you use rules in a stylesheet if they evaluate true or false.

Conditionals are set by writing @if before the expression you want to evaluate. If the expression is true, then its contents are included in the stylesheet. If the expression is false, then its contents are not included, but the contents of an @else that follows it are included.

$type: monster;

p {
  @if $type == ocean {
    color: blue;
  } @else {
    color: black;
  }
}

In that example, $type === ocean is false, so the @if contents are ignored and the @else contents are used.

p {
  color: black;
}

@for and @each Rules

Iterators like @for and @each let you repeat content in a stylesheet.

A @for statement repeats by a numerical counter defined as a variable.

It can be written as @for $counter from <start> through <end> where $counter is the name of the iterating variable, <start> is the number to start with, and <end> is the number to finish with.

It can also be written as @for $counter from <start> to <end> where $counter is still the name of the counter variable, <start> is still the number to start with, but <end> is now the number to finish before, but not include.

When <start> is greater than <end>, the counter will decrement instead of increment.

Either form of @for can be written as @for $var from <start> to <end> by <increment> or @for $var from <start> through <end> by <increment> where <incremement> is the amount the counter variable will advance.

@for $i from 1 through 5 by 2 {
  .width-#{$i} {
    width: #{$i}0em;
  }
}

@for $j from 1 to 5 by 2 {
  .height-#{$j} {
    height: #{$j}0em;
  }
}

In that example, $i is repeated from 1 through 5 by 2, which means it is repeated 3 times (1, 3, and 5). Meanwhile, $j is repeated from 1 to 5 by 2, which means it is repeated 2 times (1 and 3).

.width-1 {
  width: 10em;
}

.width-3 {
  width: 30em;
}

.width-5 {
  width: 50em;
}

.height-1 {
  height: 10em;
}

.height-3 {
  height: 30em;
}

An @each statement statement repeats through a list of values.

It can be written as @each $item in $list where $item is the name of the iterating variable and $list is the list of values being looped over.

@each $animal in (puma, sea-slug, egret, salamander) {
  .#{$animal}-icon {
    background-image: url("images/icon-#{$animal}.svg");
  }
}

In that example, a list of 4 animals is looped over to create 4 unique classnames.

.puma-icon {
  background-image: url("images/icon-puma.svg");
}

.sea-slug-icon {
  background-image: url("images/icon-sea-slug.svg");
}

.egret-icon {
  background-image: url("images/icon-egret.svg");
}

.salamander-icon {
  background-image: url("images/icon-salamander.svg");
}

It can also be written as @each $item $counter in $list where $item is still the name of the iterating variable and $list is still the list of values being looped over, but now $counter is the numerical counter.

@each $animal $i in (puma, sea-slug, egret, salamander) {
  .#{$animal}-icon {
    background-image: url("images/icon-#{$i}.svg");
  }
}

.puma-icon {
  background-image: url("images/icon-1.svg");
}

.sea-slug-icon {
  background-image: url("images/icon-2.svg");
}

.egret-icon {
  background-image: url("images/icon-3.svg");
}

.salamander-icon {
  background-image: url("images/icon-4.svg");
}

In that example, a list of 4 animals is looped over to create 4 unique classnames.

@mixin, @include, and @content rules

Mixins let you reuse rule in a stylesheet. A @mixin defines the content you want to reuse, while an @include rule includes it anywhere in your stylesheet.

Mixins are set by writing @mixin before the name of the mixin you define. This can be (optionally) followed by comma-separated variables you want to use inside of it. Mixins are then used anywhere by writing @include before the name of the mixin you are using. This is (again, optionally) followed by some comma-separated arguments you want to pass into the mixin as the (aforementioned) variables.

@mixin heading-text {
  color: #242424;
  font-size: 4em;
}

h1, h2, h3 {
  @include heading-text;
}

.some-heading-component > :first-child {
  @include heading-text;
}

In that example, @include heading-text is replaced with its contents.

h1, h2, h3 {
  color: #242424;
  font-size: 4em;
}

.some-heading-component > :first-child {
  color: #242424;
  font-size: 4em;
}

Remember, mixins can be followed by comma-separated variables you want to pass into the mixin as variables.

@mixin heading-text($color: #242424, $font-size: 4em) {
  color: $color;
  font-size: $font-size;
}

h1, h2, h3 {
  @include heading-text;
}

.some-heading-component > :first-child {
  @include heading-text(#111111, 6em);
}

In that example, @include heading-text is replaced with its contents, but this time some of their contents are customized with variables.

h1, h2, h3 {
  color: #242424;
  font-size: 4em;
}

.some-heading-component > :first-child {
  color: #111111;
  font-size: 6em;
}

Options

variables

The variables option defines global variables used when they cannot be resolved automatically.

require('postcss-advanced-variables')({
  variables: {
    'site-width': '960px'
  }
});

The variables option also accepts a function, which is given 2 arguments; the name of the unresolved variable, and the PostCSS node that used it.

require('postcss-advanced-variables')({
  variables(name, node) {
    if (name === 'site-width') {
      return '960px';
    }

    return undefined;
  }
});

.hero {
  max-width: $site-width;
}

/* after */

.hero {
  max-width: 960px;
}

unresolved

The unresolved option defines how unresolved variables, mixins, and imports should be handled. The available options are throw, warn, and ignore. The default option is to throw.

require('postcss-advanced-variables')({
  unresolved: 'ignore' // ignore unresolved variables
});

disable

The disable option defines which features should be disabled in PostCSS Advanced Variables.

The disable option can be a string or an array, and the features that can be disabled are @content, @each, @else, @if, @include, @import, @for, and @mixin.

require('postcss-advanced-variables')({
  disable: '@mixin, @include, @content' // ignore @mixin, @include, and @content at-rules
});

Import Options

These options only apply to the @import at-rule.

importPaths

The importPaths option defines a path or multiple paths used to lookup files when they cannot be found automatically.

The importPaths option can be a string or an array.

By default, imports are resolved using the Sass Import Resolve Specification.

require('postcss-advanced-variables')({
  importPaths: ['path/to/files', 'another/path/to/files']
});

importResolve

The importResolve option defines the file resolver used by imports. It is a function given 3 arguments; the url id, the current working directory, and the options processed by PostCSS Advanced Variables.

The importResolve function should return a Promise with an object containing the full path (file) and the contents of the file (contents).

const resolve = require('custom-resolver');

require('postcss-advanced-variables')({
  // a resolver may work many ways, and this is just an example
  importResolve: (id, cwd, opts) => resolve({ id, cwd });
});

importFilter

The importFilter option determines whether an import will be inlined.

The value can be a function or an regular expression. When providing a function, it is called with a single string argument id and returns true when the import should be inlined. When providing a regular expression, if the id matches the expression, the import will be inlined.

By default, imports are ignored if they begin with a protocol or protocol-relative slashes (//).

require('postcss-advanced-variables')({
  importFilter: (id) => {
    return ['ignore', 'these', 'imports'].contains(id);
  }
});

importRoot

The importRoot option defines the root directory used by imports when the current directory cannot be detected. Its default value is process.cwd().

require('postcss-advanced-variables')({
  importRoot: 'path/to/root'
});

importCache

The importCache option defines a cache made available to the options object that may be used by the file resolver.

const sharedCache = {};

require('postcss-advanced-variables')({
  importCache: sharedCache
});