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.
$ npm install postcss-custom-properties
// dependenciesvar fs =var postcss =var customProperties =// css to be processedvar css = fs// process css using postcss-custom-propertiesvar output =css
you will get:
You can also compile CSS custom properties with their fallback value.
you will get:
Note that plugin returns itself in order to expose a
that allow you to programmatically change the variables.
var variables ="--a": "b"var plugin =pluginvar result =
This might help for dynamic live/hot reloading.
Checkout tests for more.
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.
Allows you to preserve custom properties & var() usage in output.
var out =css
You can also set
preserve: "computed" to get computed resolved custom
properties in the final output.
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.
preserve is set to
"computed"), allows you to append your
variables at the end of your CSS.
Allows you to enable/disable warnings. If true, will enable all warnings.
For now, it only allow to disable messages about custom properties definition
not scoped in a
If it is set to
'error', using of undefined variable will throw an error.
Fork, work on a branch, install dependencies & run tests before submitting a PR.
$ git clone$ git checkout -b patch-1$ npm install$ npm test