PostCSS Simple Variables

PostCSS plugin for Sass-like variables.

You can use variables inside values, selectors and at-rule’s parameters.

$dir:    top;
$blue:   #056ef0;
$column: 200px;

.menu_link {
  background: $blue;
  width: $column;
}
.menu {
  width: calc(4 * $column);
  margin-$(dir): 10px;
}

.menu_link {
  background: #056ef0;
  width: 200px;
}
.menu {
  width: calc(4 * 200px);
  margin-top: 10px;
}

If you want be closer to W3C spec, you should use postcss-custom-properties and postcss-at-rules-variables plugins.

Also you should look at postcss-map for big complicated configs.

Interpolation

There is special syntax if you want to use variable inside CSS words:

$prefix: my-company-widget

$prefix { }
$(prefix)_button { }

Comments

You could use variables in comments too (for example, to generate special mdcss comments). But syntax for comment variables is different to separate them from PreCSS code examples:

$width: 100px;
/* $width: <<$(width)>> */

compiles to:

/* $width: 100px */

Escaping

If you want to escape $ in content property, use Unicode escape syntax.

.foo::before {
  content: "\0024x";
}

Usage

Step 1: Install plugin:

npm install --save-dev postcss postcss-simple-vars

Step 2: Check you project for existed PostCSS config: postcss.config.js in the project root, "postcss" section in package.json or postcss in bundle config.

If you do not use PostCSS, add it according to official docs and set this plugin in settings.

Step 3: Add the plugin to plugins list:

module.exports = {
  plugins: [
+   require('postcss-simple-vars'),
    require('autoprefixer')
  ]
}

Options

Call plugin function to set options:

    require('postcss-simple-vars')({ silent: true })

variables

Set default variables. It is useful to store colors or other constants in common file:

// config/colors.js

module.exports = {
  blue: '#056ef0'
}

// postcss.config.js

const colors = require('./config/colors')
const vars   = require('postcss-simple-vars')

module.exports = {
  plugins: [
    require('postcss-simple-vars')({ variables: colors })
  ]
}

You can set a function returning object, if you want to update default variables in webpack hot reload:

    require('postcss-simple-vars')({
      variables: function () {
        return require('./config/colors');
      }
    })

onVariables

Callback invoked once all variables in css are known. The callback receives an object representing the known variables, including those explicitly-declared by the variables option.

    require('postcss-simple-vars')({
      onVariables (variables) {
        console.log('CSS Variables');
        console.log(JSON.stringify(variables, null, 2));
      }
    })

unknown

Callback on unknown variable name. It receives node instance, variable name and PostCSS Result object.

    require('postcss-simple-vars')({
      unknown (node, name, result) {
        node.warn(result, 'Unknown variable ' + name);
      }
    })
])

silent

Left unknown variables in CSS and do not throw an error. Default is false.

only

Set value only for variables from this object. Other variables will not be changed. It is useful for PostCSS plugin developers.

keep

Keep variables as is and not delete them. Default is false.

Messages

This plugin passes result.messages for each variable:

const result = await postcss([vars]).process('$one: 1; $two: 2')
console.log(result.messages)

will output:

[
  {
    plugin: 'postcss-simple-vars',
    type: 'variable',
    name: 'one'
    value: '1'
  },
  {
    plugin: 'postcss-simple-vars',
    type: 'variable',
    name: 'two'
    value: '2'
  }
]

You can get access to this variables in result.messages also in any plugin goes after postcss-simple-vars.