PostCSS Advanced Variables [][postcss]

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

``scss
$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:

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

#### Node

Use [PostCSS Advanced Variables] to process your CSS:

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

#### PostCSS

Add [PostCSS] to your build tool:

`bash
npm install postcss --save-dev
`

Use [PostCSS Advanced Variables] as a plugin:

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

#### Gulp

Add [Gulp PostCSS] to your build tool:

`bash
npm install gulp-postcss --save-dev
`

Use [PostCSS Advanced Variables] in your Gulpfile:

`js
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:

`bash
npm install grunt-postcss --save-dev
`

Use [PostCSS Advanced Variables] in your Gruntfile:

`js
grunt.loadNpmTasks('grunt-postcss');

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

---

Features

$3

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}).

`scss
$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.

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

$3

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.

`scss
$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.

`css
p {
color: black;
}
`

$3

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 through where
$counter is the name of the iterating variable, is the number to
start with, and is the number to finish with.

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

When is greater than , the counter will decrement instead of
increment.

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

`scss
@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).

`css
.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.

`scss
@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.

`css
.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.

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

`css
.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.

$3

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.

`scss
@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.

`css
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.

`scss
@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.

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

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

---

Options

$3

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

`js
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.

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

return undefined;
}
});
`

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

/ after /

.hero {
max-width: 960px;
}
`

$3

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.

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

$3

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.

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

$3

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].

`js
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).

`js
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 (//).

`js
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().

`js
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.

`js
const sharedCache = {};

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

[cli-img]: https://img.shields.io/travis/jonathantneal/postcss-advanced-variables.svg
[cli-url]: https://travis-ci.org/jonathantneal/postcss-advanced-variables
[test-img]: https://github.com/csstools/postcss-advanced-variables/actions/workflows/test.yml/badge.svg
[test-url]: https://github.com/csstools/postcss-advanced-variables/actions/workflows/test.yml
[git-img]: https://img.shields.io/badge/chat-gitter-blue.svg
[git-url]: https://gitter.im/postcss/postcss
[npm-img]: https://img.shields.io/npm/v/postcss-advanced-variables.svg
[npm-url]: https://www.npmjs.com/package/postcss-advanced-variables

[Gulp PostCSS]: https://github.com/postcss/gulp-postcss
[Grunt PostCSS]: https://github.com/nDmitry/grunt-postcss
[PostCSS]: https://github.com/postcss/postcss
[PostCSS Advanced Variables]: https://github.com/jonathantneal/postcss-advanced-variables
[PostCSS SCSS Syntax]: https://github.com/postcss/postcss-scss
[Sass Import Resolve Specification]: https://jonathantneal.github.io/sass-import-resolve/