postcss-selector-parser

What is postcss-selector-parser?

The postcss-selector-parser npm package is a parser that helps in transforming CSS selectors. It provides a rich API to analyze and manipulate CSS selectors programmatically. This package is particularly useful for tasks related to CSS processing, such as linting, optimization, and custom transformations.

What are postcss-selector-parser's main functionalities?

Parsing and transforming selectors

This feature allows for the parsing and transformation of CSS selectors. In the provided code sample, all 'h1' tags in a selector are changed to 'h2' tags.

const parser = require('postcss-selector-parser');
const transform = selectors => {
  selectors.walkTags(tag => {
    if (tag.value === 'h1') {
      tag.value = 'h2';
    }
  });
};
const transformed = parser(transform).processSync('h1.class');

Extracting classes from selectors

This feature demonstrates how to extract class names from a selector. The code sample extracts 'class1' and 'class2' from the selector string '.class1.class2'.

const parser = require('postcss-selector-parser');
const extractClasses = selector => {
  const classes = [];
  parser(selectors => {
    selectors.walkClasses(classNode => {
      classes.push(classNode.value);
    });
  }).processSync(selector);
  return classes;
};
const classes = extractClasses('.class1.class2');

Working with pseudo classes

This feature focuses on manipulating pseudo classes within selectors. In the example, ':hover' pseudo classes are replaced with ':focus'.

const parser = require('postcss-selector-parser');
const transformPseudo = selector => {
  return parser(selectors => {
    selectors.walkPseudos(pseudo => {
      if (pseudo.value === ':hover') {
        pseudo.value = ':focus';
      }
    });
  }).processSync(selector);
};
const result = transformPseudo('a:hover');

Other packages similar to postcss-selector-parser

css-what

css-what is a CSS selector parser that can parse selectors into an understandable format but does not offer the same level of manipulation and transformation capabilities as postcss-selector-parser.

css-selector-tokenizer

css-selector-tokenizer can tokenize and parse CSS selectors. It provides a different API and approach compared to postcss-selector-parser, focusing more on the tokenization aspect rather than direct manipulation.

scss-parser

scss-parser is designed to parse SCSS syntax. While it can handle selectors within the SCSS syntax, its primary focus is broader than just selectors, making it less specialized compared to postcss-selector-parser.

README

postcss-selector-parser

Selector parser with built in methods for working with selector strings.

Install

With npm do:

npm install postcss-selector-parser

Quick Start

var parser = require('postcss-selector-parser');
var transform = function (selectors) {
    selectors.eachInside(function (selector) {
        // do something with the selector
        console.log(String(selector))
    });
};

var transformed = parser(transform).process('h1, h2, h3').result;

To normalize selector whitespace:

var parser = require('postcss-selector-parser');
var normalized = parser().process('h1, h2, h3', {lossless:false}).result;
// -> h1,h2,h3

API

Please see API.md.

Credits

• Huge thanks to Andrey Sitnik (@ai) for work on PostCSS which helped accelerate this module's development.

License

MIT

Changelog

2.2.3

• Resolves an issue where the parser would not reduce multiple spaces between an ampersand and another simple selector in lossy mode (thanks to @adam-26).