CSS AST Parser

Fast and lightweight CSS parser with AST transformations and plugin system.
Built for high performance and large stylesheets.
~360ms vs PostCSS ~1701ms

Features

• High performance parsing
• AST transformations
• Plugin system (PostCSS-like)
• Safe node mutation
• Single-line minified output
• Legacy browser support
• Zero dependencies

Installation

npm install rewcss-ast

## Installation

You can install the package from npm:

```bash
npm install rewcss-ast

Or clone the repository for development:

git clone https://github.com/DragonDragging/rewcss-ast.git
cd rewcss-ast

Usage

const fs = require("fs");
const { parse, generate, walk } = require("rewcss-ast");

// Example plugin
const plugins = [
  () => ({
    decl(node) {
      if (node.prop === "background-color") {
        node.remove();
      }
    },
    rule(node) {
      console.log("Rule:", node.selector);
    }
  })
];

const css = fs.readFileSync("./input.css", "utf-8");

const ast = parse(css, { legacySupport: true, comments: false });
walk(ast, plugins);

const out = generate(ast);
fs.writeFileSync("./output.css", out);

How It Works

The processing pipeline: CSS -> parse() -> AST -> walk() -> generate() -> CSS parse -> converts CSS into AST (optionally applies legacy browser prefixes and removing comments) walk -> applies plugins and mutates AST generate -> converts AST back to CSS

AST Structure

"nodes" - array of child declarations or rules, may include legacy prefixed versions

Example node:

{
  "type": "decl",
  "prop": "color",
  "value": "red"
}

Node types: rule - selector block decl - declaration atrule - @rules comment - comments

Plugins

Plugins return visitors.

Example: remove background-color

module.exports = function () {
    return {
        decl: {
            enter(path) {
                if (path.isDecl("background-color")) {
                    path.remove();
                }
            }
        }
    };
};

Path API

path.remove() — remove node path.replace(node) — replace node path.setProp(v) — change property path.setValue(v) — change value

Helpers: path.isDecl(name) path.isRule(selector) path.isAtRule(name)

Transformation Pipeline

1. Read CSS
2. Parse AST (optionally apply legacy support and removing comments)
3. Apply plugins
4. Generate optimized CSS

Performance

This project is optimized for speed and low memory usage. Key points: fast loops (no forEach/map) array join instead of string concat minimal allocations safe mutation traversal Designed to handle large CSS files efficiently.

Author

DragonDragging

Contact

If you find any bugs, please contact me on Discord with a detailed explanation: @dragondragging