@csstools/css-parser-algorithms

What is @csstools/css-parser-algorithms?

@csstools/css-parser-algorithms is a library designed to help parse and manipulate CSS using various algorithms. It provides tools to work with CSS syntax trees, making it easier to analyze and transform CSS code programmatically.

What are @csstools/css-parser-algorithms's main functionalities?

Parsing CSS

This feature allows you to parse a CSS string into an Abstract Syntax Tree (AST). The AST can then be used for further analysis or transformation.

const { parse } = require('@csstools/css-parser-algorithms');
const css = 'body { color: red; }';
const ast = parse(css);
console.log(ast);

Traversing AST

This feature allows you to traverse the AST nodes. You can define enter and leave functions to perform actions when entering or leaving a node.

const { parse, traverse } = require('@csstools/css-parser-algorithms');
const css = 'body { color: red; }';
const ast = parse(css);
traverse(ast, {
  enter(node) {
    console.log('Entering:', node.type);
  },
  leave(node) {
    console.log('Leaving:', node.type);
  }
});

Transforming CSS

This feature allows you to transform the CSS AST. In this example, the color property is changed from red to blue.

const { parse, transform } = require('@csstools/css-parser-algorithms');
const css = 'body { color: red; }';
const ast = parse(css);
const newAst = transform(ast, {
  enter(node) {
    if (node.type === 'Declaration' && node.property === 'color') {
      node.value = 'blue';
    }
  }
});
console.log(newAst);

Other packages similar to @csstools/css-parser-algorithms

postcss

PostCSS is a tool for transforming CSS with JavaScript plugins. It provides a similar functionality to @csstools/css-parser-algorithms in terms of parsing and transforming CSS. However, PostCSS has a larger ecosystem of plugins and is more widely used in the industry.

css-tree

CSS Tree is a toolset for CSS including a fast CSS parser, walker, generator, and lexer. It offers similar capabilities to @csstools/css-parser-algorithms but is known for its performance and detailed error reporting.

csstree

CSSTree is a detailed and fast CSS parser and generator. It provides similar functionalities to @csstools/css-parser-algorithms but focuses more on performance and detailed error messages.

README

CSS Parser Algorithms

Implemented from : https://www.w3.org/TR/2021/CRD-css-syntax-3-20211224/

API

Read the API docs

Usage

Add CSS Parser Algorithms to your project:

npm install @csstools/css-parser-algorithms @csstools/css-tokenizer --save-dev

CSS Parser Algorithms only accepts tokenized CSS. It must be used together with @csstools/css-tokenizer.

import { tokenizer, TokenType } from '@csstools/css-tokenizer';
import { parseComponentValue } from '@csstools/css-parser-algorithms';

const myCSS =  `@media only screen and (min-width: 768rem) {
	.foo {
		content: 'Some content!' !important;
	}
}
`;

const t = tokenizer({
	css: myCSS,
});

const tokens = [];

{
	while (!t.endOfFile()) {
		tokens.push(t.nextToken());
	}

	tokens.push(t.nextToken()); // EOF-token
}

const options = {
	onParseError: ((err) => {
		throw err;
	}),
};

const result = parseComponentValue(tokens, options);

console.log(result);

Available functions

• parseComponentValue
• parseListOfComponentValues
• parseCommaSeparatedListOfComponentValues

Utilities

gatherNodeAncestry

The AST does not expose the entire ancestry of each node. The walker methods do provide access to the current parent, but also not the entire ancestry.

To gather the entire ancestry for a a given sub tree of the AST you can use gatherNodeAncestry. The result is a Map with the child nodes as keys and the parents as values. This allows you to lookup any ancestor of any node.

import { parseComponentValue } from '@csstools/css-parser-algorithms';

const result = parseComponentValue(tokens, options);
const ancestry = gatherNodeAncestry(result);

Options

{
	onParseError?: (error: ParseError) => void
}

onParseError

The parser algorithms are forgiving and won't stop when a parse error is encountered. Parse errors also aren't tokens.

To receive parsing error information you can set a callback.

Parser errors will try to inform you about the point in the parsing logic the error happened. This tells you the kind of error.

Goals and non-goals

Things this package aims to be:

• specification compliant CSS parser
• a reliable low level package to be used in CSS sub-grammars

What it is not:

• opinionated
• fast
• small
• a replacement for PostCSS (PostCSS is fast and also an ecosystem)