PostCSS Custom Selectors

PostCSS plugin to transform W3C CSS Extensions(Custom Selectors) to more compatible CSS.

Installation

$ npm install postcss-custom-selectors

Quick Start

Example 1:

// dependencies
var fs = require('fs')
var postcss = require('postcss')
var selector = require('postcss-custom-selectors')

// css to be processed
var css = fs.readFileSync('input.css', 'utf8')

// process css using postcss-custom-selectors
var output = postcss()
  .use(selector())
  .process(css)
  .css
  
console.log('\n====>Output CSS:\n', output)

Or just：

var output = postcss(selector())
  .process(css)
  .css

input.css：

@custom-selector :--heading h1, h2, h3, h4, h5, h6;

article :--heading + p { 
  margin-top: 0;
}

You will get:

article h1 + p,
article h2 + p,
article h3 + p,
article h4 + p,
article h5 + p,
article h6 + p { 
  margin-top: 0;
}

CSS syntax

@custom-selector = @custom-selector :<extension-name> <selector>;

How to use

The custom selector is a pseudo-class, so we must use the :-- to defined it.

For example to simulate :any-link selector：

Example 2:

input.css:

@custom-selector :--any-link :link, :visited;

a:--any-link {
  color: blue;
}

output:

a:link,
a:visited {
  color: blue;
}

Multiple selectors

@custom-selector it doesn’t support call multiple custom selector in the same selector, e.g.

Example 3:

@custom-selector :--heading h1, h2, h3, h4, h5, h6;
@custom-selector :--any-link :link, :visited;

.demo :--heading, a:--any-link { 
  font-size: 32px;
}

This will throw an error CSS code.

.demo h1,
.demo h2,
.demo h3,
.demo h4,
.demo h5,
.demo h6,:link,
:visited  { 
  font-size: 32px;
}

Node Watch

Dependence chokidar module.

var fs = require('fs')
var chokidar = require('chokidar')
var postcss = require('postcss')
var selector = require('postcss-custom-selectors')

var src = 'input.css'

console.info('Watching…\nModify the input.css and save.')

chokidar.watch(src, {
  ignored: /[\/\\]\./,
  persistent: true
}).on('all',
  function(event, path, stats) {
    var css = fs.readFileSync(src, 'utf8')
    var output = postcss(selector())
      .process(css)
      .css
    fs.writeFileSync('output.css', output)
  })

Grunt

module.exports = function(grunt) {
  grunt.initConfig({
    pkg: grunt.file.readJSON('package.json'),
    postcss: {
      options: {
        processors: [
          require('autoprefixer-core')({ browsers: ['> 0%'] }).postcss, //Other plugin
          require('postcss-custom-selectors')(),
        ]
      },
      dist: {
        src: ['src/*.css'],
        dest: 'build/grunt.css'
      }
    }
  });

  grunt.loadNpmTasks('grunt-contrib-uglify');
  grunt.loadNpmTasks('grunt-postcss');

  grunt.registerTask('default', ['postcss']);
}

Gulp

var gulp = require('gulp');
var rename = require('gulp-rename');
var postcss = require('gulp-postcss');
var selector = require('postcss-custom-selectors')
var autoprefixer = require('autoprefixer-core')

gulp.task('default', function () {
    var processors = [
        autoprefixer({ browsers: ['> 0%'] }), //Other plugin
        selector()
    ];
    gulp.src('src/*.css')
        .pipe(postcss(processors))
        .pipe(rename('gulp.css'))
        .pipe(gulp.dest('build'))
});
gulp.watch('src/*.css', ['default']);

Options

1. `lineBreak`(default: `true`)

Set whether multiple selector wrap.The default is turning on to be a newline.

Close the line breaks.

var options = {
  lineBreak: false
}

var output = postcss(selector(options))
  .process(css)
  .css

In the 'Example 1' input.css will output:

article h1 + p, article h2 + p, article h3 + p, article h4 + p, article h5 + p, article h6 + p {
  margin-top: 0;
}

2. `extensions` (default: `{}`)

This option allows you to customize an object to set the <extension-name> (selector alias) and <selector>, these definitions will cover the same alias of @custom-selector in CSS.

var options = {
  extensions: {
    ':--any' : 'section, article, aside, nav'
  }
}

var output = postcss(selector(options))
  .process(css)
  .css;

input.css

@custom-selector :--any .foo, .bar; /* No effect */
:--any h1 {
  margin-top: 16px;
}

output:

/* No effect */
section h1,
article h1,
aside h1,
nav h1 {
  margin-top: 16px;
}

Contributing

Install the relevant dependent module.
Respect coding style（Install EditorConfig）.
Add test cases in the test directory.
Run test.

$ git clone https://github.com/postcss/postcss-custom-selectors.git
$ git checkout -b patch
$ npm install
$ npm test