css

What is css?

The 'css' npm package is a powerful library for parsing, manipulating, and generating CSS. It allows developers to programmatically work with CSS stylesheets, making it easier to handle dynamic styling in web applications.

What are css's main functionalities?

Parsing CSS

This feature allows you to parse a CSS string into a JavaScript object. The parsed result includes detailed information about styles, rules, and selectors, which can be manipulated or queried.

const css = require('css');
const stylesheet = css.parse('body { font-size: 12px; }');
console.log(stylesheet);

Stringifying CSS

This feature converts a JavaScript object representing a CSS stylesheet back into a CSS string. This is useful for generating CSS styles dynamically based on logic within your application.

const css = require('css');
const obj = {
  type: 'stylesheet',
  stylesheet: {
    rules: [{
      type: 'rule',
      selectors: ['body'],
      declarations: [{
        type: 'declaration',
        property: 'margin',
        value: '0 auto'
      }]
    }]
  }
};
const stringifiedCSS = css.stringify(obj);
console.log(stringifiedCSS);

Manipulating CSS

This feature allows you to manipulate an existing CSS stylesheet by adding, modifying, or removing rules and declarations. This example demonstrates adding a new declaration to an existing rule.

const css = require('css');
const stylesheet = css.parse('h1 { color: red; }');
stylesheet.stylesheet.rules[0].declarations.push({
  type: 'declaration',
  property: 'font-size',
  value: '20px'
});
const newCSS = css.stringify(stylesheet);
console.log(newCSS);

Other packages similar to css

postcss

PostCSS is a tool for transforming CSS with JavaScript plugins. These plugins can lint your CSS, support variables and mixins, transpile future CSS syntax, inline images, and more. It is more plugin-driven compared to 'css', offering a broader range of transformations.

sass

Sass (Syntactically Awesome Style Sheets) is a preprocessor scripting language that is interpreted or compiled into Cascading Style Sheets (CSS). It provides more features like variables, nested rules, and mixins compared to the basic CSS manipulations offered by 'css'.

less

Less is a backward-compatible language extension for CSS. This is very similar to Sass but uses a different syntax. It provides variables, mixins, and functions which allows you to make CSS that is more maintainable, themable, and extendable than the 'css' package.

README

css

CSS parser / stringifier.

Installation

$ npm install css

Usage

var css = require('css');
var obj = css.parse('body { font-size: 12px; }', options);
css.stringify(obj, options);

API

css.parse(code, [options])

Accepts a CSS string and returns an AST object.

options:

• silent: silently fail on parse errors.
• source: the path to the file containing css. Makes errors and source maps more helpful, by letting them know where code comes from.

css.stringify(object, [options])

Accepts an AST object (as css.parse produces) and returns a CSS string.

options:

• indent: the string used to indent the output. Defaults to two spaces.
• compress: omit comments and extraneous whitespace.
• sourcemap: return a sourcemap along with the CSS output. Using the source option of css.parse is strongly recommended when creating a source map. Specify sourcemap: 'generator' to return the SourceMapGenerator object instead of serializing the source map.
• inputSourcemaps: (enabled by default, specify false to disable) reads any source maps referenced by the input files when generating the output source map. When enabled, file system access may be required for reading the referenced source maps.

Example

var ast = css.parse('body { font-size: 12px; }', { source: 'source.css' });

var css = css.stringify(ast);

var result = css.stringify(ast, { sourcemap: true });
result.code // string with CSS
result.map // source map object

Errors

Errors thrown during parsing have the following properties:

• message: String. The full error message with the source position.
• reason: String. The error message without position.
• filename: String or undefined. The value of options.source if passed to css.parse. Otherwise undefined.
• line: Integer.
• column: Integer.
• source: String. The portion of code that couldn't be parsed.

When parsing with the silent option, errors are listed in the parsingErrors property of the stylesheet node instead of being thrown.

If you create any errors in plugins such as in rework, you must set the same properties for consistency.

AST

Interactively explore the AST with http://iamdustan.com/reworkcss_ast_explorer/.

Common properties

All nodes have the following properties.

position

Information about the position in the source string that corresponds to the node.

Object:

• start: Object:
  • line: Number.
  • column: Number.
• end: Object:
  • line: Number.
  • column: Number.
• source: String or undefined. The value of options.source if passed to css.parse. Otherwise undefined.
• content: String. The full source string passed to css.parse.

The line and column numbers are 1-based: The first line is 1 and the first column of a line is 1 (not 0).

The position property lets you know from which source file the node comes from (if available), what that file contains, and what part of that file was parsed into the node.

type

String. The possible values are the ones listed in the Types section below.

parent

A reference to the parent node, or null if the node has no parent.

Types

The available values of node.type are listed below, as well as the available properties of each node (other than the common properties listed above.)

stylesheet

The root node returned by css.parse.

• stylesheet: Object:
  • rules: Array of nodes with the types rule, comment and any of the at-rule types.
  • parsingErrors: Array of Errors. Errors collected during parsing when option silent is true.

rule

• selectors: Array of Strings. The list of selectors of the rule, split on commas. Each selector is trimmed from whitespace and comments.
• declarations: Array of nodes with the types declaration and comment.

declaration

• property: String. The property name, trimmed from whitespace and comments. May not be empty.
• value: String. The value of the property, trimmed from whitespace and comments. Empty values are allowed.

comment

A rule-level or declaration-level comment. Comments inside selectors, properties and values etc. are lost.

• comment: String. The part between the starting /* and the ending */ of the comment, including whitespace.

charset

The @charset at-rule.

• charset: String. The part following @charset .

custom-media

The @custom-media at-rule.

• name: String. The ---prefixed name.
• media: String. The part following the name.

document

The @document at-rule.

• document: String. The part following @document .
• vendor: String or undefined. The vendor prefix in @document, or undefined if there is none.
• rules: Array of nodes with the types rule, comment and any of the at-rule types.

font-face

The @font-face at-rule.

• declarations: Array of nodes with the types declaration and comment.

host

The @host at-rule.

• rules: Array of nodes with the types rule, comment and any of the at-rule types.

import

The @import at-rule.

• import: String. The part following @import .

keyframes

The @keyframes at-rule.

• name: String. The name of the keyframes rule.
• vendor: String or undefined. The vendor prefix in @keyframes, or undefined if there is none.
• keyframes: Array of nodes with the types keyframe and comment.

keyframe

• values: Array of Strings. The list of “selectors” of the keyframe rule, split on commas. Each “selector” is trimmed from whitespace.
• declarations: Array of nodes with the types declaration and comment.

media

The @media at-rule.

• media: String. The part following @media .
• rules: Array of nodes with the types rule, comment and any of the at-rule types.

namespace

The @namespace at-rule.

• namespace: String. The part following @namespace .

page

The @page at-rule.

• selectors: Array of Strings. The list of selectors of the rule, split on commas. Each selector is trimmed from whitespace and comments.
• declarations: Array of nodes with the types declaration and comment.

supports

The @supports at-rule.

• supports: String. The part following @supports .
• rules: Array of nodes with the types rule, comment and any of the at-rule types.

Example

CSS:

body {
  background: #eee;
  color: #888;
}

Parse tree:

{
  "type": "stylesheet",
  "stylesheet": {
    "rules": [
      {
        "type": "rule",
        "selectors": [
          "body"
        ],
        "declarations": [
          {
            "type": "declaration",
            "property": "background",
            "value": "#eee",
            "position": {
              "start": {
                "line": 2,
                "column": 3
              },
              "end": {
                "line": 2,
                "column": 19
              }
            }
          },
          {
            "type": "declaration",
            "property": "color",
            "value": "#888",
            "position": {
              "start": {
                "line": 3,
                "column": 3
              },
              "end": {
                "line": 3,
                "column": 14
              }
            }
          }
        ],
        "position": {
          "start": {
            "line": 1,
            "column": 1
          },
          "end": {
            "line": 4,
            "column": 2
          }
        }
      }
    ]
  }
}

License

MIT