custom-property-extract

Extract CSS custom properties (a.k.a CSS variables) and their values from SCSS, SASS and CSS stylesheets.

Since they can be overwritten in selectors, every custom property returns an array of all possible values directly extracted from the provided stylesheet. See Example to get a quick overview on how things work.

Install

Install custom-property-extract by running the following command:

npm install custom-property-extract

Usage

extract(sourceStyle, extractOptions)

const path = require('path');
const { extract } = require('custom-property-extract');

const customProperties = extract(path.resolve('./path/to/stylesheet.scss'), { syntax: 'scss' });

Alternatively, you can directly pass the content of the stylesheet in the sourceStyle argument by setting the source option to "content":

const path = require('path');
const { extract } = require('custom-property-extract');

const style = `
  :root {
    --my-variable: blue;
  }
`;

const customProperties = extract(style, {
  syntax: 'scss',
  source: 'content',
});

extractOptions

Name	Type	Required	Default	Description
mode	{String}	false	"simple"	Output mode ("simple", "full")
syntax	{String}	false	"css"	Syntax of the source stylesheet ("css", "scss", "sass")
source	{String}	false	"file"	Type of the source ("file", "content")
prefix	{Boolean}	false	true	Determines whether to prefix custom properties with --.

Example

Consider the following CSS stylesheet:

@charset "UTF-8";
:root {
  --color-primary: #ff017d;
  --color-secondary: #000;
  --color-background: white;
  --color-foreground: var(--color-secondary);
  --radius-round: 50% 50%;
  --spacing-s: 5rem;
  --shadow-xs: 1px 2px 3px 4px rgba(0,0,0,0.25), inset 4px 3px 2px 1px #fff;
  --border-light: 1px solid rgba(0,0,0,0.15);
  --amount-suffix-content: '€';
  --margin-default: 0.5rem !important;
}

[data-theme="dark"] {
  --color-primary: #cf689a;
  --color-secondary: blue;
  --color-background: var(--color-background);
}

[data-theme="dark"].nested {
  --color-primary: blue;
  --width-header: calc(100vh - (3rem / 2));
}

[data-lang="us"] {
  --amount-suffix-content: '$';
}

@media screen and (min-width: 960px) {
  :root {
    --color-primary: blue;
  }
}

Simple mode

Using custom-property-extract's extract function will output the following object:

{
  '--color-primary': [ '#ff017d', '#cf689a', 'blue', 'blue' ],
  '--color-secondary': [ '#000', 'blue' ],
  '--color-background': [ 'white', 'var(--color-background)' ],
  '--color-foreground': [ 'var(--color-secondary)' ],
  '--radius-round': [ '50% 50%' ],
  '--spacing-s': [ '5rem' ],
  '--shadow-xs': [ '1px 2px 3px 4px rgba(0,0,0,0.25), inset 4px 3px 2px 1px #fff' ],
  '--border-light': [ '1px solid rgba(0,0,0,0.15)' ],
  '--amount-suffix-content': [ "'€'", "'$'" ],
  '--margin-default': [ '0.5rem !important' ],
  '--width-header': [ 'calc(100vh - (3rem / 2))' ]
}

Full mode

Using custom-property-extract's extract function with mode set to "full" will output the following object:

{
  '--color-primary': [
    { value: '#ff017d', selector: ':root' },
    { value: '#cf689a', selector: '[data-theme="dark"]' },
    { value: 'blue', selector: '[data-theme="dark"].nested' },
    {
      value: 'blue',
      selector: ':root',
      media: 'screen and (min-width: 960px)'
    }
  ],
  '--color-secondary': [
    { value: '#000', selector: ':root' },
    { value: 'blue', selector: '[data-theme="dark"]' }
  ],
  '--color-background': [
    { value: 'white', selector: ':root' },
    {
      value: 'var(--color-background)',
      selector: '[data-theme="dark"]'
    }
  ],
  '--color-foreground': [ { value: 'var(--color-secondary)', selector: ':root' } ],
  '--radius-round': [ { value: '50% 50%', selector: ':root' } ],
  '--spacing-s': [ { value: '5rem', selector: ':root' } ],
  '--shadow-xs': [
    {
      value: '1px 2px 3px 4px rgba(0,0,0,0.25), inset 4px 3px 2px 1px #fff',
      selector: ':root'
    }
  ],
  '--border-light': [ { value: '1px solid rgba(0,0,0,0.15)', selector: ':root' } ],
  '--amount-suffix-content': [
    { value: "'€'", selector: ':root' },
    { value: "'$'", selector: '[data-lang="us"]' }
  ],
  '--margin-default': [ { value: '0.5rem !important', selector: ':root' } ],
  '--width-header': [
    {
      value: 'calc(100vh - (3rem / 2))',
      selector: '[data-theme="dark"].nested'
    }
  ]
}

Naming a custom property definition

When using the full mode, you may provide a name to a custom property definition by adding a comment starting with the @case keyword.

Example input

:root {
  // @case Default color.
  --color-primary: #ff017d;
  --color-secondary: #000;
}

.app {
  --color-primary: gray;

  .has-errors {
    /** @case Color when something wrong happened. */
    --color-primary: red;
  }
}

Example output

{
  '--color-primary': [
    { selector: ':root ', value: '#ff017d', name: 'Default color.' },
    { selector: '.app ', value: 'gray' },
    {
      selector: '.app .has-errors ',
      value: 'red',
      name: 'Color when something wrong happened.'
    }
  ],
  '--color-secondary': [ { selector: ':root ', value: '#000' } ]
}