postcss-assets

PostCSS Assets is an asset manager for CSS. It isolates stylesheets from environmental changes, gets image sizes and inlines files.

Table of contents

• Installation
• Usage
• URL resolution
  • Load paths
  • Base path
  • Base URL
  • Relative paths
• Cachebuster
• Image dimensions
• Inlining files
• Full list of options

Installation

npm install postcss-assets --save-dev

Usage

Gulp PostCSS

gulp.task('assets', function () {
  var postcss = require('gulp-postcss');
  var assets  = require('postcss-assets');

  return gulp.src('source/*.css')
    .pipe(postcss([assets({
      loadPaths: ['images/']
    })]))
    .pipe(gulp.dest('build/'));
});

Grunt PostCSS

var assets  = require('postcss-assets');

grunt.initConfig({
  postcss: {
    options: {
      processors: [
        assets({
          loadPaths: ['images/']
        })
      ]
    },
    dist: { src: 'build/*.css' }
  },
});

Note: all of the listed options below are parameters for the assets object, not the top level postcss options object.

URL resolution

These options isolate stylesheets from environmental changes.

Load paths

To make PostCSS Assets search for files in specific directories, define load paths:

var options = {
  loadPaths: ['fonts/', 'media/patterns/', 'images/']
};

Example:

body {
  background: resolve('foobar.jpg');
  background: resolve('icons/baz.png');
}

PostCSS Assets would look for the files relative to the source file, then in load paths, then in the base path. If it succeed, it would resolve a true URL:

body {
  background: url('/media/patterns/foobar.jpg');
  background: url('/images/icons/baz.png');
}

Base path

If the root directory of your site is not where you execute PostCSS Assets, correct it:

var options = {
  basePath: 'source/'
};

PostCSS Assets would treat source directory as / for all URLs and load paths would be relative to it.

Base URL

If the URL of your base path is not /, correct it:

var options = {
  baseUrl: 'http://example.com/wp-content/themes/'
};

Relative paths

To make resolved paths relative to the input file, set a flag:

var options = {
  relative: true
};

To relate to a particular directory, set it as a string:

var options = {
  relative: 'assets/css'
};

Cachebuster

PostCSS Assets can bust assets cache:

var options = {
  cachebuster: true
};

Example:

body {
  background: resolve('/images/icons/baz.png');
}

PostCSS Assets will change urls depending on asset’s modification date:

body {
  background: url('/images/icons/baz.png?14a931c501f');
}

To define a custom cachebuster pass a function as an option:

var options = {
  cachebuster: function (filePath, urlPathname) {
    return fs.statSync(filePath).mtime.getTime().toString(16);
  }
};

If the returned value is falsy, no cache busting is done for the asset.

If the returned value is an object the values of pathname and/or query are used to generate a cache busted path to the asset.

If the returned value is a string, it is added as a query string.

The returned values for query strings must not include the starting ?.

Busting the cache via path:

var options = {
  cachebuster: function (filePath, urlPathname) {
    var hash = fs.statSync(filePath).mtime.getTime().toString(16);
    return {
      pathname: path.dirname(urlPathname)
        + '/' + path.basename(urlPathname, path.extname(urlPathname))
        + hash + path.extname(urlPathname),
      query: false // you may omit this one
    }
  }
};

Image dimensions

PostCSS Assets calculates dimensions of PNG, JPEG, GIF, SVG and WebP images:

body {
  width: width('images/foobar.png'); /* 320px */
  height: height('images/foobar.png'); /* 240px */
  background-size: size('images/foobar.png'); /* 320px 240px */
}

To correct the dimensions for images with a high density, pass it as a second parameter:

body {
  width: width('images/foobar.png', 2); /* 160px */
  height: height('images/foobar.png', 2); /* 120px */
  background-size: size('images/foobar.png', 2); /* 160px 120px */
}

Inlining files

PostCSS inlines files to a stylesheet in Base64 encoding:

body {
  background: inline('images/foobar.png');
}

SVG files would be inlined unencoded, because then they benefit in size.

Full list of options

Option	Description	Default
basePath	Root directory of the project.	.
baseUrl	URL of the project when running the web server.	/
cachebuster	If cache should be busted. Pass a function to define custom busting strategy.	false
loadPaths	Specific directories to look for the files.	[]
relative	Directory to relate to when resolving URLs. When true, relates to the input file. When false, disables relative URLs.	false
cache	When true, if the input file not been modifed, use the results before cached.	false