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 runtime dependencies, except for the minification tool used for bundling (fingerprinting has no dependencies).

The plugin requires Jekyll version 3 or 4. It is tested with Ruby MRI 2.7 and later.

The plugin works with Jekyll's watch mode (auto-regeneration, Jekyll option --watch), but not with incremental feature enabled (Jekyll option --incremental).

Features

There are two features: fingerprinting with MD5 digest over the contents of the asset file (any type of file will do), 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. UglifyJS 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 browsers and intermediate proxies to cache the asset for a very long time. Calculating MD5 digest over the contents of the file 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 ships as a RubyGem. To install:

1. Add the following line to the Gemfile of your site:

   gem 'jekyll-minibundle'
   

2. Run bundle install.

3. Instruct Jekyll to load the gem by adding this line to the configuration file of your site (_config.yml):

   plugins:
     - jekyll/minibundle
   

   (Use the gems key instead of plugins for Jekyll older than v3.5.0.)

An alternative to using the plugins configuration option is to add the _plugins/minibundle.rb file to your site project with this line:

require 'jekyll/minibundle'

You must allow Jekyll to use custom plugins. That is, do not enable Jekyll's safe configuration option.

Asset fingerprinting

If you just want to have an MD5 fingerprint in your asset's path, use the ministamp Liquid tag in a Liquid template file. For example, fingerprinting CSS styles:

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

When it's time to render the ministamp tag, the plugin copies the source file (_assets/site.css, the first tag argument) to the specified destination path (assets/site.css, the second tag argument) in Jekyll's site destination directory. The filename will contain a fingerprint.

The tag outputs the asset destination path, encoded for HTML, into Liquid's template rendering outcome. For example, when site.baseurl is empty:

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

Another example, this time fingerprinting an image and using the absolute_url Liquid filter of Jekyll to render the absolute URL of the image in the src attribute:

<img src="{{ "/" | absolute_url }}{% ministamp _assets/dog.jpg assets/dog.jpg %}" alt="My dog smiling to the camera" title="A photo of my dog" width="195" height="258" />

This feature can be combined with asset generation tools external to Jekyll. For example, you can configure Sass to take input files from _assets/styles/*.scss and to produce output to _tmp/site.css. Then, you use the ministamp tag to copy the file with a fingerprint to Jekyll's site destination directory:

<link rel="stylesheet" href="{{ site.baseurl }}/{% ministamp _tmp/site.css assets/site.css %}">

ministamp call syntax

The argument for the ministamp tag must be in YAML syntax, and parsing the argument as YAML must result either in a String or a Hash. What you saw previously was the argument being parsed as a String; it's effectively a shorthand version of passing the argument as a Hash with certain keys. That is, in the following call:

{% ministamp _tmp/site.css assets/site.css %}

the argument is a String: "_tmp/site.css assets/site.css". The call is equivalent to the following call with a Hash argument:

{% ministamp { source_path: _tmp/site.css, destination_path: assets/site.css } %}

The Hash argument allows expressing more options and quoting source_path and destination_path values, if needed.

The supported keys for the Hash argument are:

Key	Required?	Value type	Value example	Default value	Description
source_path	yes	string	'_tmp/site.css'	-	The source path of the asset file, relative to the site directory.
destination_path	yes	string	'assets/site.css'	-	The destination path of the asset file, relative to Jekyll's site destination directory. If the value begins with / and render_basename_only is false, ministamp's output will begin with /.
render_basename_only	no	boolean	true	false	If true, ministamp's rendered URL will be the basename of the asset destination path. See Separating asset destination path from generated URL for more.

With a Hash argument, the plugin processes source_path and destination_path values through a tiny template engine. This allows you to use Liquid's variables as input to ministamp tag. An example with Liquid's assign tag:

{% assign asset_dir = 'assets' %}
<link rel="stylesheet" href="{% ministamp { source_path: _tmp/site.css, destination_path: '{{ asset_dir }}/site.css' } %}">

The above would use assets/site.css as the destination path.

Note that you must quote destination_path's value, otherwise YAML does not recognize it as a proper string.

To refer to Jekyll's configuration options (_config.yml) in the template, prefix the variable name with site.. For example, to refer to baseurl option, use syntax {{ site.baseurl }} in the template.

See Variable templating for details about the template syntax.

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 markup tag contains the path to the bundle file, and the Jekyll's site destination directory will have the bundle file at that path. The path will contain an MD5 fingerprint.

Place the minibundle Liquid block into the Liquid template file where you want the block's generated markup to appear. Write bundling configuration inside the block in YAML syntax. For example, to bundle a set of JavaScript sources:

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

Then, specify the command for launching your favorite minifier in _config.yml:

baseurl: ''

minibundle:
  minifier_commands:
    js: node_modules/.bin/uglifyjs

When it's time to render the minibundle block, the plugin launches the minifier and connects to it with a Unix pipe. The plugin feeds the contents of the asset files in source_dir directory as input to the minifier (stdin). The feeding order is the order of the files in the assets key in the block configuration. The plugin expects the minifier to produce output (stdout) and writes it to the file at destination_path in Jekyll's site destination directory. The filename will contain a fingerprint.

The block outputs <link> (for css type) or <script> (for js type) HTML element into Liquid's template rendering outcome. Continuing the example above, the block's output will be:

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

You can pass custom attributes, like id="my-scripts" and async above, to the generated markup with attributes map inside the minibundle block.

As shown above for the baseurl key, you can use Liquid template syntax inside the contents of the block. Liquid renders block contents before the minibundle block gets the turn to render itself. Just ensure that block contents will result in valid YAML.

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

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

And then specify the minifier command in _config.yml:

minibundle:
  minifier_commands:
    css: _bin/remove_whitespace
    js: node_modules/.bin/uglifyjs

minibundle call syntax

Use css or js as the argument to the opening tag, for example {% minibundle css %}.

The block contents must be in YAML syntax. The supported keys are:

Key	Value type	Value example	Default value	Description
source_dir	string	-	'_assets'	The source directory of assets, relative to the site directory. You can use period (.) to select the site directory itself.
assets	array of strings	['deps/one', 'deps/two', 'app']	[]	Array of assets relative to source_dir directory, without type extension. These are the asset files to be bundled, in order, into one bundle destination file.
destination_path	string	-	'assets/site'	The destination path of the bundle file, without type extension, relative to Jekyll's site destination directory. If the value begins with / and baseurl is empty, baseurl will be set to '/' implicitly.
baseurl	string	'{{ site.baseurl }}/'	''	If nonempty, the bundle destination URL inside minibundle's rendered HTML element will be this value prepended to the destination path of the bundle file. Ignored if destination_baseurl is nonempty.
destination_baseurl	string	'{{ site.cdn_baseurl }}/'	''	If nonempty, the bundle destination URL inside minibundle's rendered HTML element will be this value prepended to the basename of the bundle destination path. See Separating asset destination path from generated URL for more.
attributes	map of keys to string values	{id: my-link, media: screen}	{}	Custom HTML element attributes to be added to minibundle's rendered HTML element.
minifier_cmd	string	'node_modules/.bin/uglifyjs'	-	Minifier command specific to this bundle. See Minifier command specification for more.

Minifier command specification

You can specify minifier commands in three places:

1. In _config.yml (as shown earlier):

   minibundle:
     minifier_commands:
       css: _bin/remove_whitespace
       js: node_modules/.bin/uglifyjs
   

2. As environment variables:

   export JEKYLL_MINIBUNDLE_CMD_CSS=_bin/remove_whitespace
   export JEKYLL_MINIBUNDLE_CMD_JS="node_modules/.bin/uglifyjs"
   

3. Inside the minibundle block with minifier_cmd option, allowing blocks to have different commands from each other:

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

These ways of specification are listed in increasing order of specificity. Should multiple commands apply to a block, the most specific one wins. For example, the minifier_cmd option inside the {% minibundle js }% block overrides the setting in the $JEKYLL_MINIBUNDLE_CMD_JS 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 site destination directory.

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

<!-- BAD: unless assets dir is excluded, both src.css and dest.css will be copied to site destination directory -->
<link rel="stylesheet" href="{{ site.baseurl }}/{% ministamp assets/src.css assets/dest.css %}" media="screen, projection">

By default, Jekyll includes this file to the site destination 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's site generation excludes underscore directories (that is, directories whose name begins with underscore character), consider using the following directory layout:

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

However, Jekyll's watch mode (auto-regeneration) does monitor files inside underscore directories. If such a file is modified, the watch mode triggers site generation. For Minibundle's functionality, this is beneficial: it allows the plugin to check if assets need to be updated to the site destination directory.

The exclude Jekyll configuration option affects Jekyll's watch mode. Given the recommended directory layout above, if you set the following in _config.yml:

exclude:
  - _assets
  - _tmp

Then Jekyll won't see if files inside those directories have changed and the plugin won't get the chance to update assets to the site destination directory. So, don't explicitly exclude the _assets and _tmp directories.

See Jekyll configuration for more about excluding files and directories.

Development mode

If you set the $JEKYLL_MINIBUNDLE_MODE environment variable to development, then the plugin will copy asset files as is to Jekyll's site destination directory and omit fingerprinting.

The development mode changes minibundle block's destination_path option to be the base directory for files mentioned in the assets option. 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

Alternatively, you can enable development mode from _config.yml:

minibundle:
  mode: development

Should both be defined, the setting from the environment variable wins.

Variable templating

The template engine used by ministamp tag's Hash argument has syntax resembling the ones of Liquid and Mustache, with {{ and }} tags surrounding the variable to be substituted into the output string. For example, given Liquid variable var = 'foo', the template begin{{ var }}end results in beginfooend.

The engine supports variable substitution only. It does not support other expressions. If you need to, you can write complex expressions in Liquid, store the result to a variable, and use the variable in the template.

If you need literal { or } characters in the template, you can escape them with backslash. For example, \{ results in { in the output. To output backslash character itself, write it twice: \\ results in \ in the output.

Inside variable subsitution (between {{ and }}), anything before the closing }} tag is interpreted as part of the variable name, except that the engine removes any leading and trailing whitespace from the name. For example, in the template {{ var } }}, var } is treated as the name of the variable.

A reference to undefined variable results in empty string. For example, begin{{ nosuch }}end will output beginend if there's no variable named nosuch.

Separating asset destination path from generated URL

Use the render_basename_only: true option of the ministamp tag and the destination_baseurl option of the minibundle block to separate the destination path of the asset file from the generated URL of the asset. This allows you to serve the asset from a separate domain, for example.

Example usage, with the following content in _config.yml:

cdn_baseurl: 'https://cdn.example.com'

For the ministamp tag:

<link rel="stylesheet" href="{{ site.cdn_baseurl }}/css/{% ministamp { source_path: '_tmp/site.css', destination_path: assets/site.css, render_basename_only: true } %}">

The asset file will be in Jekyll's site destination directory with path assets/site-ff9c63f843b11f9c3666fe46caaddea8.css, and Liquid's rendering will result in:

<link rel="stylesheet" href="https://cdn.example.com/css/site-ff9c63f843b11f9c3666fe46caaddea8.css">

For the minibundle block:

{% minibundle js %}
source_dir: _assets/scripts
destination_path: assets/site
destination_baseurl: '{{ site.cdn_baseurl }}/js/'
assets:
  - dependency
  - app
{% endminibundle %}

The bundle file will be in Jekyll's site destination directory with path assets/site-4782a1f67803038d4f8351051e67deb8.js, and Liquid's rendering will result in:

<script type="text/javascript" src="https://cdn.example.com/js/site-4782a1f67803038d4f8351051e67deb8.js"></script>

Capturing Liquid output

Use Liquid's capture block to store output rendered inside the block to a variable, as a string. Then you can process the string as you like.

For example:

{% capture site_css %}{% ministamp _assets/site.css assets/site.css %}{% endcapture %}
<link rel="stylesheet" href="{{ site_css | remove_first: "assets/" }}">

Liquid's rendering outcome:

<link rel="stylesheet" href="site-390be921ee0eff063817bb5ef2954300.css">

Example site

See the sources of an example site.

Known caveats

The plugin does not work with Jekyll's incremental rebuild feature (Jekyll option --incremental).

License

MIT. See LICENSE.txt.