Jekyll Minibundle plugin

A straightforward asset bundling plugin for Jekyll, utilizing external minification tool of your choice. It provides asset concatenation for bundling and asset fingerprinting with MD5 digest for cache busting. There are no other runtime dependencies besides the minification tool (not even other gems).

Tested with Ruby MRI 1.9.3, 2.0, and 2.1. Ruby 1.8 is not supported.

The plugin works with Jekyll's watch (auto-regeneration) mode.

Features

There are two features: asset fingerprinting with MD5 digest over the contents of the asset, and asset bundling combined with the first feature.

Asset bundling consists of concatenation and minification. The plugin implements concatenation and leaves choosing the minification tool up to you. UglifyJS2 is a good and fast minifier, for example. The plugin connects to the minifier with standard unix pipe, feeding asset file contents to it in desired order via standard input, and reads the result from standard output.

Why is this good? A fingerprint in asset's path is the recommended way to handle caching of static resources, because you can allow caching the asset forever. Calculating MD5 digest over the contents of the asset is fast and the resulting digest is reasonably unique to be generated automatically.

Asset bundling is good for reducing the number of requests to the backend upon page load. The minification of stylesheets and JavaScript sources makes asset sizes smaller and thus faster to load over network.

Usage

The plugin is shipped as a RubyGem:

$ gem install jekyll-minibundle

Add file _plugins/minibundle.rb to your Jekyll site project with this line:

require 'jekyll/minibundle'

You must allow Jekyll to use custom plugins. In Jekyll's configuration, do not enable safe setting.

Asset fingerprinting

Asset fingerprinting is intended to be used together with Compass and similar asset generation tools that have their own configuration for input sources.

Configure Compass to take inputs from _assets/styles/*.scss and to put output to _tmp/site.css. Use ministamp tag to copy the processed style asset to the generated site:

<link href="{% ministamp _tmp/site.css assets/site.css %}" rel="stylesheet" media="screen, projection">

Output, containing the MD5 digest of the file in the filename:

<link href="assets/site-390be921ee0eff063817bb5ef2954300.css" rel="stylesheet" media="screen, projection">

This feature does not require any external tools.

Asset bundling

This is a straightforward way to bundle assets with any minification tool that supports reading input from STDIN and writing the output to STDOUT. You write the configuration for input sources directly into the content file where you want the markup tag for the bundle file to appear. The outcome will be a markup tag containing the path to the bundle file, and the generated site will have the bundle file in that path. The MD5 digest of the file will be included in the filename.

Place minibundle block with configuration into your content file where you want the generated markup to appear. For example, to bundle a set of JavaScript sources:

{% minibundle js %}
source_dir: _assets/scripts
destination_path: assets/site
assets:
  - dependency
  - app
attributes:
  id: my-scripts
{% endminibundle %}

Then, specify the command for launching your favorite minifier in $JEKYLL_MINIBUNDLE_CMD_JS environment variable. For example, when launching Jekyll:

$ JEKYLL_MINIBUNDLE_CMD_JS='./node_modules/.bin/uglifyjs --' jekyll

You can pass custom attributes to the generated markup with attributes map in the configuration.

Output in the content file:

<script src="assets/site-8e764372a0dbd296033cb2a416f064b5.js" type="text/javascript" id="my-scripts"></script>

For bundling CSS assets, you use css as the argument to minibundle block:

{% minibundle css %}
source_dir: _assets/styles
destination_path: assets/site
assets:
  - reset
  - common
attributes:
  media: screen
{% endminibundle %}

And then specify the command for launching bundling in $JEKYLL_MINIBUNDLE_CMD_CSS environment variable.

Recommended directory layout

It's recommended that you exclude the files you use as asset sources from Jekyll itself. Otherwise, you end up with duplicate files in the output directory.

For example, in the following snippet we're using assets/src.css as asset source to ministamp tag:

<link href="{% ministamp assets/src.css assets/dest.css %}" rel="stylesheet" media="screen, projection">

By default, Jekyll includes this file to the output directory. As a result, there will be both src.css and dest-<md5>.css files in _site/assets/ directory, which you probably do not want.

In order to avoid this, exclude the asset source file from Jekyll. Because Jekyll excludes directories beginning with underscore character (_), consider the following directory layout:

_assets/ for JS and CSS assets handled by the plugin that are in version control
_tmp/ for temporary JS and CSS assets handled by the plugin that are not in version control (for example, Compass output files)
assets/ for images and other assets handled by Jekyll directly

See Jekyll configuration for more about excluding files and directories.

Development mode

The plugin has one more trick in its sleeves. If you set environment variable $JEKYLL_MINIBUNDLE_MODE to development, then the plugin will copy asset files as is to the destination directory (using destination_path as directory for minibundle block), and omit fingerprinting. This is useful in development workflow, where you need the filenames and line numbers of the original asset sources.

$ JEKYLL_MINIBUNDLE_MODE=development jekyll serve --watch

Example site

See the contents of test/fixture/site directory.

License

MIT. See LICENSE.txt.