css-tree

What is css-tree?

The css-tree npm package is a tool for parsing and manipulating CSS. It allows users to parse CSS strings into an abstract syntax tree (AST), walk over nodes in the tree, generate CSS strings, and more. It is useful for tasks such as CSS minification, linting, and transformation.

What are css-tree's main functionalities?

Parsing CSS to AST

This feature allows you to parse a CSS string and convert it into an abstract syntax tree (AST) for further manipulation or analysis.

const csstree = require('css-tree');
const ast = csstree.parse('.example { color: red; }');

Walking the AST

This feature enables you to traverse the AST and apply functions or extract information from specific nodes.

csstree.walk(ast, function(node) {
  if (node.type === 'ClassSelector') {
    console.log(node.name);
  }
});

Generating CSS from AST

After manipulating the AST, you can generate a CSS string from the modified AST, which can be used in stylesheets or injected into web pages.

const modifiedAST = csstree.parse('.example { color: blue; }');
const css = csstree.generate(modifiedAST);

Minifying CSS

css-tree can be used to minify CSS by parsing it with compression options and then translating the AST back to a CSS string.

const compressedCSS = csstree.translate(csstree.parse('.example { color: red; }', { compress: true }));

Other packages similar to css-tree

postcss

PostCSS is a tool for transforming CSS with JavaScript plugins. It can do similar tasks as css-tree, such as parsing, walking the AST, and generating CSS. PostCSS is plugin-based, which makes it more extensible and allows for a wide range of transformations.

sass

Sass is a preprocessor scripting language that is interpreted or compiled into CSS. It offers more syntactic features compared to css-tree, such as variables, nesting, and mixins, but it is not primarily focused on parsing and manipulating existing CSS.

less

Less is another CSS pre-processor, similar to Sass, that extends the capabilities of CSS with dynamic behavior such as variables, mixins, operations, and functions. Less and css-tree serve different purposes, with Less focusing on writing CSS in a more functional way and css-tree on parsing and manipulation.

clean-css

clean-css is a fast and efficient CSS optimizer for Node.js and the browser. It focuses on minification, which is one of the features of css-tree, but does not provide a general-purpose CSS parsing and manipulation API.

README

• CSS syntax reference
• CSS syntax validator

Related:

• csstree-validator – NPM package to validate CSS
• stylelint-csstree-validator – plugin for stylelint to validate CSS
• Gulp plugin
• Sublime plugin
• VS Code plugin

Install

> npm install css-tree

Usage

var csstree = require('css-tree');

csstree.walk(csstree.parse('.a { color: red; }'), function(node) {
  console.log(node.type);
});
// Class
// SimpleSelector
// Selector
// Property
// Identifier
// Value
// Declaration
// Block
// Ruleset
// StyleSheet

API

parse(source[, options])

Parse CSS to AST.

NOTE: Currenly parser omit redundant separators, spaces and comments (except exclamation comments, i.e. /*! comment */) on AST build.

Options:

• context String – parsing context, useful when some part of CSS is parsing (see below)
• property String – make sense for declaration context to apply some property specific parse rules
• positions Boolean – should AST contains node position or not, store data in info property of nodes (false by default)
• filename String – filename of source that adds to info when positions is true, uses for source map generation (<unknown> by default)
• line Number – initial line number, useful when parse fragment of CSS to compute correct positions
• column Number – initial column number, useful when parse fragment of CSS to compute correct positions

Contexts:

• stylesheet (default) – regular stylesheet, should be suitable in most cases
• atrule – at-rule (e.g. @media screen, print { ... })
• atruleExpression – at-rule expression (screen, print for example above)
• ruleset – rule (e.g. .foo, .bar:hover { color: red; border: 1px solid black; })
• selector – selector group (.foo, .bar:hover for ruleset example)
• simpleSelector – selector (.foo or .bar:hover for ruleset example)
• block – block content w/o curly braces (color: red; border: 1px solid black; for ruleset example)
• declaration – declaration (color: red or border: 1px solid black for ruleset example)
• value – declaration value (red or 1px solid black for ruleset example)

// simple parsing with no options
var ast = csstree.parse('.example { color: red }');

// parse with options
var ast = csstree.parse('.foo.bar', {
    context: 'simpleSelector',
    positions: true
});

clone(ast)

Make an AST node deep copy.

var orig = csstree.parse('.test { color: red }');
var copy = csstree.clone(orig);

csstree.walk(copy, function(node) {
    if (node.type === 'Class') {
        node.name = 'replaced';
    }
});

console.log(csstree.translate(orig));
// .test{color:red}
console.log(csstree.translate(copy));
// .replaced{color:red}

translate(ast)

Converts AST to string.

var ast = csstree.parse('.test { color: red }');
console.log(csstree.translate(ast));
// > .test{color:red}

translateWithSourceMap(ast)

The same as translate() but also generates source map (nodes should contain positions in info property).

var ast = csstree.parse('.test { color: red }', {
    filename: 'my.css',
    positions: true
});
console.log(csstree.translateWithSourceMap(ast));
// { css: '.test{color:red}', map: SourceMapGenerator {} }

walk(ast, handler)

Visit all nodes of AST and call handler for each one. handler receives three arguments:

• node – current AST node
• item – node wrapper when node is a list member; this wrapper contains references to prev and next nodes in list
• list – reference to list when node is a list member; it's useful for operations on list like remove() or insert()

Context for handler an object, that contains references to some parent nodes:

• root – refers to ast or root node
• stylesheet – refers to closest StyleSheet node, it may be a top-level or at-rule block stylesheet
• atruleExpression – refers to AtruleExpression node if current node inside at-rule expression
• ruleset – refers to Ruleset node if current node inside a ruleset
• selector – refers to Selector node if current node inside a selector
• declaration – refers to Declaration node if current node inside a declaration
• function – refers to closest Function or FunctionalPseudo node if current node inside one of them

// collect all urls in declarations
var csstree = require('./lib/index.js');
var urls = [];
var ast = csstree.parse(`
  @import url(import.css);
  .foo { background: url('foo.jpg'); }
  .bar { background-image: url(bar.png); }
`);

csstree.walk(ast, function(node) {
    if (this.declaration !== null && node.type === 'Url') {
        var value = node.value;

        if (value.type === 'Raw') {
            urls.push(value.value);
        } else {
            urls.push(value.value.substr(1, value.value.length - 2));
        }
    }
});

console.log(urls);
// [ 'foo.jpg', 'bar.png' ]

walkRules(ast, handler)

Same as walk() but visits Ruleset and Atrule nodes only.

walkRulesRight(ast, handler)

Same as walkRules() but visits nodes in reverse order (from last to first).

walkDeclarations(ast, handler)

Visit all declarations.

License

MIT

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