Sprockets inspired web assets compiler for Node.JS
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Mincer - assets processor

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JavaScript port of Sprockets (v2.6.0). It features same declarative dependency management (with exactly same language) for CSS and JavaScript and preprocessor pipeline. Mincer allows you to write assets in the languages like: CoffeeScript, LESS, Stylus.

See Sprockets and Mincer API Documentation for more details.


Install Mincer from npm registry:

$ npm install mincer

Or install bleeding edge version from GitHub repo:

$ npm install git://github.com/nodeca/mincer.git

Using Mincer from CLI

To use Mincer from CLI, you will need to intall it globally:

$ npm install mincer -g

Usage is really simple (see mincer -h for details):

$ mincer --include assets/javascripts \
         --include assets/stylesheets \
         --output public/assets \
         application.js application.css

If you are using mincer CLI often, you would probably want to "preset" some of the options/arguments for your project. Just create .mincerrc file and put argument you want in it. For example:

--include assets/javascripts --include assets/stylesheets --output public/assets

Understanding the Mincer Environment

You'll need an instance of the Mincer.Environment class to access and serve assets from your application.

The Environment has methods for retrieving and serving assets, manipulating the load path, and registering processors. It is also used by Mincer.Server which can be mounted directly as request event handler of http.Server or as connect middleware.

The Load Path

The load paths is an ordered list of directories that Mincer uses to search for assets.

In the simplest case, a Mincers environment's load path will consist of a single directory containing your application's asset source files. When mounted, server will serve assets from this directory as if they were static files in your public root.

The power of the load path is that it lets you organize your source files into multiple directories -- even directories that live outside your application -- and combine those directories into a single virtual filesystem. That means you can easily bundle JavaScript, CSS and images into a library and import them into your application.

Manipulating the Load Path

To add a directory to your environment's load path, use the appendPath and prependPath methods. Directories at the beginning of the load path have precedence over subsequent directories.

environment = new Mincer.Environment();

In general, you should append to the path by default and reserve prepending for cases where you need to override existing assets.

Accessing Assets

Once you've set up your environment's load path, you can mount the environment as a server and request assets via HTTP. You can also access assets programmatically from within your application.

Logical Paths

Assets in Mincer are always referenced by their logical path.

The logical path is the path of the asset source file relative to its containing directory in the load path. For example, if your load path contains the directory app/assets/javascripts:

Asset source file Logical path
app/assets/javascripts/application.js application.js
app/assets/javascripts/models/project.js models/project.js

In this way, all directories in the load path are merged to create a virtual filesystem whose entries are logical paths.

Serving Assets Over HTTP

When you mount an environment, all of its assets are accessible as logical paths underneath the mount point. For example, if you mount your environment at /assets and request the URL /assets/application.js, Mincer will search your load path for the file named application.js and serve it.

var connect = require('connect');
var Mincer  = require('mincer');

var environment = new Mincer.Environment();

var app = connect();
app.use('/assets', Mincer.createServer(environment));
app.use(function (req, res) {
  // your application here...

Accessing Assets Programmatically

You can use the findAsset method to retrieve an asset from a Mincers environment. Pass it a logical path and you'll get a BundledAsset instance back.

If it's first time you have requested asset you'll need to compile it. Call toString on the resulting asset to access its contents, length to get its length in bytes, mtime to query its last-modified time, and pathname to get its full path on the filesystem.

environment.findAsset('application.js').compile(function (err, asset) {
  asset.toString(); // resulting contents
  asset.length;     // length in bytes
  asset.mtime;      // last modified time
  asset.pathname;   // full path on the filesystem


In comparison to Sprockets, where assets is being compiled (rendered) the same time (in a synchronous fashion) it is initiated. In comparison we have compilation "delayed", that leads into the situation that real file digest is available for us ONLY after file was really compiled. Here's simple example of asset_path helper:

function asset_path(pathname) {
  var asset = environment.findAsset(pathname);
  return asset ? asset.digestPath : '';

The helper above works perfectly with static assets (those who have no processors assigned, e.g. images, fonts, etc.), but it will return you wrong digest path for application.js unless you compile it first:

var asset = environment.findAsset('application.js');

asset.digestPath; // uses initial digest (calculated against original source)

asset.compile(function (err, asset) {
  asset.digestPath; // correct digest path

  asset = environment.findAsset('application.js');
  asset.digestPath; // correct digest again, unless application.js was changed

Using Engines

Asset source files can be written in another language, like Stylus or CoffeeScript, and automatically compiled to CSS or JavaScript by Mincer. Compilers for these languages are called engines.

Engines are specified by additional extensions on the asset source filename. For example, a CSS file written in Stylus might have the name layout.css.styl, while a JavaScript file written in CoffeeScript might have the name dialog.js.coffee.

Styling with Stylus

Stylus is a revolutionary new language, providing an efficient, dynamic, and expressive way to generate CSS. Supporting both an indented syntax and regular CSS style.

If the stylus Node module is available to your application, you can use Stylus to write CSS assets in Mincer. Use the extension .css.styl.

Styling with LESS

LESS extends CSS with dynamic behavior such as variables, mixins, operations and functions.

If the less Node module is available to your application, you can use LESS to write CSS assets in Mincer. Use the extension .css.less.

Scripting with CoffeeScript

CoffeeScript is a language that compiles to the "good parts" of JavaScript, featuring a cleaner syntax with array comprehensions, classes, and function binding.

If the coffee-script Node module is available to your application, you can use CoffeeScript to write JavaScript assets in Mincer. Use the extension .css.coffee.

JavaScript Templating with Haml Coffee

Mincer supports JavaScript templates for client-side rendering of strings or markup. JavaScript templates have the special format extension .jst and are compiled to JavaScript functions.

When loaded, a JavaScript template function can be accessed by its logical path as a property on the global JST object. Invoke a template function to render the template as a string. The resulting string can then be inserted into the DOM.

// templates/hello.jst.hamlc
%div= Hello, %span= #{ @name }!
// application.js
//= require templates/hello
$("#hello").html(JST["templates/hello"]({ name: "Sam" }));

Mincer supports two template languages: Haml Coffee and Jade.

If coffee-script and haml-coffee are available to your application, you can use Haml Cofee templates in Mincer. Haml Coffee templates have the extension .jst.hamlc.

If jade Node module is available to your application, you can use Jade templates in Mincer. Jade templates have the extension .jst.jade. To use compiled templates you will need to require Jade runtime before calling renderer functions.

Invoking JavaScript with EJS

Mincer provides an EJS engine for preprocessing assets using embedded JavaScript code. Append .ejs to a CSS or JavaScript asset's filename to enable the EJS engine.

You will need ejs Node module available to your application.

Note: Mincer processes multiple engine extensions in order from right to left, so you can use multiple engines with a single asset. For example, to have a CoffeeScript asset that is first preprocessed with EJS, use the extension .js.coffee.ejs.

JavaScript code embedded in an asset is evaluated in the context of a Mincer.Context instance for the given asset. Common uses for EJS include:

  • embedding another asset as a Base64-encoded data: URI with the asset_data_uri helper
  • inserting the URL to another asset, such as with the asset_path helper (you must register your own helper for this purpose, but it's dead simple).
  • embedding other application resources, such as a localized string database, in a JavaScript asset via JSON
  • embedding version constants loaded from another file

Using helpers

Mincer provides an easy way to add your own helpers for engines:

environment.registerHelper('version', function () {
  return require(__dirname, '/package.json').version;

Now, you can call that helper with EJS like this:

var APP = window.APP = {version: '<%= version() %>'};

NOTICE Helpers currently work for EJS and Stylus only. So to use them with Less you will need to add EJS engine as well:

// file: foobar.less.ejs
.btn {
  background: url('<%= asset_path('bg.png') %>');

Managing and Bundling Dependencies

You can create asset bundles -- ordered concatenations of asset source files -- by specifying dependencies in a special comment syntax at the top of each source file.

Mincer reads these comments, called directives, and processes them to recursively build a dependency graph. When you request an asset with dependencies, the dependencies will be included in order at the top of the file.

The Directive Processor

Mincer runs the directive processor on each CSS and JavaScript source file. The directive processor scans for comment lines beginning with = in comment blocks at the top of the file.

//= require jquery
//= require jquery-ui
//= require backbone
//= require_tree .

The first word immediately following = specifies the directive name. Any words following the directive name are treated as arguments. Arguments may be placed in single or double quotes if they contain spaces, similar to commands in the Unix shell.

Note: Non-directive comment lines will be preserved in the final asset, but directive comments are stripped after processing. Mincer will not look for directives in comment blocks that occur after the first line of code.

Supported Comment Types

The directive processor understands comment blocks in three formats:

/* Multi-line comment blocks (CSS, Stylus, JavaScript)
 *= require foo

// Single-line comment blocks (Stylus, JavaScript)
//= require foo

# Single-line comment blocks (CoffeeScript)
#= require foo

Mincer Directives

You can use the following directives to declare dependencies in asset source files.

For directives that take a path argument, you may specify either a logical path or a relative path. Relative paths begin with ./ and reference files relative to the location of the current file.

The require Directive

require path inserts the contents of the asset source file specified by path. If the file is required multiple times, it will appear in the bundle only once.

The include Directive

include path works like require, but inserts the contents of the specified source file even if it has already been included or required.

The require_directory Directive

require_directory path requires all source files of the same format in the directory specified by path. Files are required in alphabetical order.

The require_tree Directive

require_tree path works like require_directory, but operates recursively to require all files in all subdirectories of the directory specified by path.

The require_self Directive

require_self tells Mincer to insert the body of the current source file before any subsequent require or include directives.

The depend_on Directive

depend_on path declares a dependency on the given path without including it in the bundle. This is useful when you need to expire an asset's cache in response to a change in another file.

The stub Directive

stub path allows dependency to be excluded from the asset bundle. The path must be a valid asset and may or may not already be part of the bundle. Once stubbed, it is blacklisted and can't be brought back by any other require.


Great thanks to Sam Stephenson and Joshua Peek for the Sprockets, the most awesome and powerfull web assets processor I ever used, and which became a great source of inspiration (and model of almost all logic behind Mincer). Special thanks to Joshua for his assistance in hacking into Sprockets sources.


Aleksey V Zapparov (follow @zapparov on twitter).


Copyright (c) 2012 Vitaly Puzrin

Released under the MIT license. See LICENSE for details.