postcss-custom-properties

What is postcss-custom-properties?

The postcss-custom-properties npm package is a PostCSS plugin that allows you to use CSS Custom Properties (also known as CSS variables) in environments that do not support them natively. It transforms CSS variables into static values based on your configurations, making it easier to maintain themes and styles dynamically across your project.

What are postcss-custom-properties's main functionalities?

Transform CSS Custom Properties

This feature allows the transformation of CSS custom properties into their corresponding static values. It is useful for supporting older browsers that do not understand CSS variables.

/* Input CSS */
:root {
  --main-color: red;
}

a {
  color: var(--main-color);
}

/* Output CSS */
a {
  color: red;
}

Preserve option

With the preserve option set to true, the plugin outputs both the transformed static value and the original variable. This is useful for progressive enhancement.

/* Input CSS */
:root {
  --main-color: red;
}

a {
  color: var(--main-color);
}

/* Output CSS with preserve: true */
a {
  color: red;
  color: var(--main-color);
}

Other packages similar to postcss-custom-properties

cssnext

cssnext is a PostCSS plugin that allows you to use future CSS features today. It includes support for CSS custom properties among other features. Compared to postcss-custom-properties, cssnext offers a broader range of CSS features but might be heavier due to its comprehensive nature.

postcss-preset-env

postcss-preset-env lets you convert modern CSS into something most browsers can understand, determining the polyfills you need based on your targeted browsers or runtime environments. It includes handling of CSS custom properties as part of its feature set, similar to postcss-custom-properties, but is more configurable and includes various stages of CSS specifications.

README

postcss-custom-properties

PostCSS plugin to transform W3C CSS Custom Properties for cascading variables syntax to more compatible CSS.

N.B. The transformation is not complete. It currently just aims to provide a future-proof way of using a limited subset (to top-level :root selector) of the features provided by native CSS custom properties.
Read #1 & #9 to know why this limitation exists.

Works great with postcss-calc.

Installation

$ npm install postcss-custom-properties

Usage

// dependencies
var fs = require("fs")
var postcss = require("postcss")
var customProperties = require("postcss-custom-properties")

// css to be processed
var css = fs.readFileSync("input.css", "utf8")

// process css using postcss-custom-properties
var output = postcss()
  .use(customProperties())
  .process(css)
  .css

Using this input.css:

:root {
  --color: red;
}

div {
  color: var(--color);
}

you will get:

div {
  color: red;
}

Checkout tests for more.

Options

preserve (default: false)

Allow you to preserve custom properties & var() usage in output.

var out = postcss()
  .use(customProperties({preserve: true}))
  .process(css)
  .css

variables (default: {})

Allow you to pass an object of variables for :root. These definitions will override any that exist in the CSS. The keys are automatically prefixed with the CSS -- to make it easier to share variables in your codebase.

---

Contributing

Work on a branch, install dev-dependencies, respect coding style & run tests before submitting a bug fix or a feature.

$ git clone https://github.com/postcss/postcss-custom-properties.git
$ git checkout -b patch-1
$ npm install
$ npm test

Changelog

License