postcss-custom-properties

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

Per w3c specifications, the usage of var() is limited to property values. Do not expect the plugin to transform var() in media queries or in selectors.

N.B. The transformation is not complete and cannot be (dynamic cascading variables based on custom properties relies on the DOM tree). It currently just aims to provide a future-proof way of using a limited subset (to :root selector) of the features provided by native CSS custom properties. Since we do not know the DOM in the context of this plugin, we cannot produce safe output. Read #1 & #9 to know why this limitation exists.

If you are looking for a full support of CSS custom properties, please follow the opened issue for runtime support.

N.B.² If you are wondering why there is a different plugin (postcss-css-variables) that claims to do more than this plugin, be sure to understand the explanation above about limitation. This plugins have a behavior that is not reflecting the specifications.

This plugin 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

`strict` (default: `true`)

Per specifications, all fallbacks should be added since we can't verify if a computed value is valid or not. This option allows you to avoid adding too many fallback values in your CSS.

`preserve` (default: `false`)

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

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

You can also set preserve: "computed" to get computed resolved custom properties in the final output. Handy to make them available to your JavaScript.

`variables` (default: `{}`)

Allows 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.

`appendVariables` (default: `false`)

If preserve is set to true (or "computed"), allows you to append your variables at the end of your CSS.

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

joeybaker / postcss-custom-properties Goto Github PK