NPM support for Sass

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Getting some npm in your Sass

eyeglass is a node-sass (github) extension manager built on top of npm. Using eyeglass, you can bring the power of node modules to your Sass files.

Installing eyeglass

# for programatic functionality
npm install eyeglass --save-dev

Adding eyeglass modules to your project

eyeglass modules are regular npm modules. Install them into your project just like any other item.

npm install my_eyeglass_module --save-dev

Once installed via npm, an eyeglass module can:

  • Provide stylesheets that you can import with special node_module syntax.
  • Add additional custom functions to Sass that are written in javascript.

In Sass files, you can reference the eyeglass module with standard Sass import syntax: @import "my_eyeglass_module/file";. The my_eyeglass_module will be resolved to the correct directory in your node modules, and the file will then resolve using the standard import rules for Sass.

Working with assets

It's quite common to need to refer to assets from within your stylesheets. Eyeglass provides core support for exposing assets to your stylesheets for your application or from an eyeglass module and generating urls to those assets as well as making sure only those assets that you actually use end up in your built application.

Exposing assets

The addSource method on eyeglass.assets is how you add assets to your application. The path passed to asset-url() is going to be relative to the directory that you pass to addSource.

Given the following assets directory structure:

└── assets/
    ├── images/
    │   ├── foo/
    │   │   └── image1.png
    │   └── unused.gif
    ├── js/
    │   └── app.js
    └── scss/
        └── app.scss

The simplest way to expose your assets to eyeglass is to add your assets directory as an eyeglass asset source. Using a simple node script we can compile a Sass file.

#!/usr/bin/env node
var path = require("path");
var sass = require("node-sass");
var Eyeglass = require("eyeglass").Eyeglass;
var rootDir = __dirname;
var assetsDir = path.join(rootDir, "assets");

var options = { ... node-sass options ... };

// specifying root lets the script run from any directory instead of having to be in the same directory.
options.root = rootDir;

// where assets are installed by eyeglass to expose them according to their output url.
// If not provided, assets are not installed unless you provide a custom installer.
options.buildDir = path.join(rootDir, "dist");

// prefix to give assets for their output url.
options.assetsHttpPrefix = "assets";

var eyeglass = new Eyeglass(options, sass);

// Add assets except for js and sass files
// The url passed to asset-url should be
// relative to the assets directory specified.
eyeglass.assets.addSource(assetsDir, {
  globOpts: { ignore: ["**/*.js", "**/*.scss"] }

// Standard node-sass rendering of a single file.
sass.render(eyeglass.sassOptions(), function(err, result) {
  // handle results

Referencing Assets

To reference an asset in your application or within your own module you can simply @import "assets". To reference assets that are in a module that you have a direct dependency on, you can @import "<module>/assets". For example: @import "my-theme/assets" would import the assets from the my-theme eyeglass module.

Importing assets for an application or module returns an automatically generated Sass file that registers asset information with the eyeglass assets Sass module.

Then you can refer to that asset using the fully qualified source url of the asset. This url must include the module prefix when referencing the asset. For example background: asset-url("images/foo.png") would import a file images/foo.png that is relative to the assetsDir.

To refer to an asset in your module, include the module name as a directory prefix when invoking asset-url. For example asset-url("my-theme/icons/party.png") would import the file icons/party.png that is exposed by the my-theme module. Even within the my-theme module, this prefix must be used when referring to the assets of that module.

Astute readers will have noted that there is a possible namespace collision if you have a directory in your application with the same name as a module. This is on purpose: it lets you replace module assets with your own assets if you need to do so by overriding them in your own application.

Asset URL Manipulation

By default, eyeglass will namespace module asset urls according to their eyeglass module name and both application and module assets urls will be placed within folder specified by the assetsHttpPrefix option. However, an application or framework can chose to override the url scheme for assets by defining an asset resolver.

Example: Adding a modification timestamp to assets as a query parameter.

  eyeglass.assets.resolver(function(assetFile, assetUri, oldResolver, done) {
    var fs = require("fs");
    var mtime = fs.statSync(assetFile).mtime.getTime();
    done(null, {
      path: assetUri,
      query: mtime.toString()

Example: hashing assets by md5sum.

eyeglass.assets.resolver(function(assetFile, assetUri, oldResolver, done) {
  var path = require("path");
  var fs = require("fs");
  var md5 = require("MD5");
  var prefix = "/" + eyeglass.options.assetsHttpPrefix + "/";
  fs.readFile(assetFile, function(err, buffer) {
    if (err) {
    } else {
      done(null, {
        path: prefix + md5(buffer) + path.extname(assetFile)

Asset Installation

By using Eyeglass's asset installation system, you can ensure that only those assets that are referenced in your stylesheets will be part of your application when it is built.

Once an asset's url is fully resolved, the asset probably needs to be installed into a location from where it can be served as that url. The simplest way to do this is to specify the buildDir option to eyeglass. Once that is specified the resolved url will be used to copy the file to a location relative to the build directory.

In order to allow for asset pipeline integration (E.g. writing to a Vinyl file) and more complex application needs, it's possible to chain or override the default eyeglass asset installer.

Installer Example: Logging installed assets:

eyeglass.assets.installer(function(assetFile, assetUri, oldInstaller, cb) {
  // oldInstaller is the standard eyeglass installer in this case.
  // We proxy to it for logging purposes.
  oldInstaller(assetFile, assetUri, function(err, result) {
    if (err) {
      console.log("Error installing '" + assetFile + "': " + err.toString());
    } else {
      console.log("Installed Asset '" + assetFile + "' => '" + result + "'");
    cb(err, result);

More on Assets

The code samples here are actually derived from a simple eyeglass project. You can view the actual code as a gist.

Assets are complex and the asset configuration of Eyeglass is very flexible. For more documentation see the asset documentation.

Writing an eyeglass module with Sass files

To create an eyeglass module with Sass files, place the files inside of a sass directory in your npm module.

|- /
  |- eyeglass-exports.js
  |- package.json
  |- sass
    |- index.scss (or .sass)

eyeglass will automatically map the first directory of @import statements to the correct node-module directory if there is a eyeglass module with that eyeglass name. Because Sass uses a global namespace, it's recommended that you namespace-prefix any mixins you create in order to avoid collisions.

In keeping with node's conventions, eyeglass modules can create an index.scss file in any folder instead of defining a file of the same name as a folder in order to be the main entry point for a sass module having submodules.

Building sass files with eyeglass support

The easiest way to use eyeglass is to use an eyeglass-aware build-tool plugin. The following plugins are available:

Integrating with other build systems

Eyeglass is designed to be easy to use with any node-sass based compilation system.

var Eyeglass = require("eyeglass").Eyeglass;
var sass = require("node-sass")
var sassOptions = { ... } ; // options for node-sass
var eyeglass = new Eyeglass(sassOptions);

// futher configuration of the eyeglass instance can happen here.

// Expose images in the assets/images directory as /images on the
// website by putting the images we reference with asset-url()
// into the public/images directory.
eyeglass.assets("assets/images", "images", "public/images");

// Expose fonts in the assets/fonts directory as /fonts on the
// website by putting the fonts we reference with asset-url()
// into the public/fonts directory.
eyeglass.assets("assets/fonts", "fonts", "public/fonts");

// These options can be passed to any sass build tool that passes
// options through to node-sass.
sass.render(eyeglass.sassOptions(), function(error, result) {
  if (error) {
    //handle the compilation error
  } else {
    // write the result.css output to a file.

Example: integration with grunt and grunt-sass

sass: {
    options: require("eyeglass").Eyeglass({
        sourceMap: true
    dist: {
        files: {
            'public/css/main.css': 'sass/main.scss'

TODO: Detailed build integration guide as details emerge.

  • Assets integration
  • Per-css callback for import-once support.
  • etc.

Writing an eyeglass module with Custom Functions

node-sass allows you to register custom functions for advanced functionality. Eyeglass allows any node modules that are tagged with eyeglass-module to be automatically loaded into eyeglass. To tag your module as an eyeglass module, add the eyeglass-module keyword to your package.json

  "keywords": ["eyeglass-module", "sass", ...],
  "main": "eyeglass-exports.js",

Your requirable module exports an object that describes your module's structure and can expose javascript functions as sass functions. Below is an example eyeglass exports file:

"use strict";

var path = require("path");

module.exports = function(eyeglass, sass) {
  return {
    sassDir: path.join(__dirname, "sass"),
    functions: {
      "hello($name: 'World')": function(name, done) {
        done(sass.types.String("Hello, " + name.getValue()));

If your package.json main file is already in use for something else, you can still export eyeglass functions by specifying eyeglass: 'path/to/eyeglass-exports.js' or by specifying an eyeglass object with an exports attribute:

  "main": "lib/my-awesome-main-file.js",
  "eyeglass": {
    "exports": "lib/eyeglass-exports.js"

If you need the top level import to be named differently than the name of your npm module (this is not best practice) then you can specify a name attribute for the eyeglass object in your package.json. The following example would allow @import "foo"; to import index.scss from your package's sass directory.

  "name": "eyeglass-foo",
  "eyeglass": {
    "name": "foo"


Any sass files imported from your node modules will only ever be imported once per CSS output file. Note that Sass files imported from the Sass load path will have the standard Sass @import behavior.