Noble Modules

A NobleJS production

Copyright © 2011 Barnesandnoble.com llc. Released under the MIT License.

Introduction

Noble Modules is an implementation of the CommonJS Modules/2.0 draft specification.

Modules/2.0 is designed to enable the creation of JavaScript modules in the same style as Modules/1.1, which was popularized by Node's module implementation. However, unlike Modules/1.1, Modules/2.0 was built from the ground up to support the browser.

Environment

Noble Modules was constructed to work in modern browser environments. It uses ECMAScript 5 features heavily, and assumes browsers follow the HTML5 standard when it comes to script loading and the events that accompany that process.

Unfortunately, many browsers in use today (the most relevant, perhaps, being Internet Explorer 8 and Safari 5) do not completely support ECMAScript 5. And Internet Explorer has always had a nonstandard script-loading implementation; even Internet Explorer 10 (platform preview 1) does not rectify this situation. Fortunately, these problems are not insurmountable: the former can be overcome with the es5-shim library, and the latter by using the included nobleModulesInIE.js module provider plug-in described below.

The unit tests for Noble Modules are known to all pass in the following browsers:

• Chrome ≥12
• Firefox ≥4 (with failures when run on the filesystem instead of on HTTP, due to bug #621276)
• Safari ≥5 (with es5-shim)
• Internet Explorer ≥9 (with nobleModulesInIE.js)

Plug-ins and Other Extras

We bundle two module provider plug-ins with Noble Modules:

• naked.js allows the use of "naked" module files, i.e. those consisting only of module code sections (in the style of Modules/1.1). It uses XMLHTTPRequest (via jQuery) to load the file contents, parses out require calls, and uses them to wrap the module code section inside a Modules/2.0 module.declare call before using eval to introduce the module into the environment. It uses the //@ sourceURL annotation for easier debugging.
• nobleModulesInIE.js allows Noble Modules to work in Internet Explorer by using the same technique, although without the require-parsing and wrapper construction. This allows the core nobleModules.js code to stay clean for those who do not need to support Internet Explorer's degenerate script-loading implementation.

Additionally, Noble Modules automatically memoizes a nobleModules module which has several methods useful for debugging or other special requirements:

• require("nobleModules").setDebugOptions({ disableCaching, warnAboutUndeclaredDependencies })
• require("nobleModules").reset({ mainModuleDirectory, withDebugOptions, keepPluginOverrides })

Finally, an extensive suite of QUnit tests is included for your perusal.

Comparison to Existing Implementations

Noble Modules has several advantages over existing implementations of the Modules/2.0 spec:

• It takes care not to pollute the global scope (which is kind of the whole point of a JavaScript module system): there is no nobleModules global!
• It does not provide the same module twice, i.e. only a single <script> tag is ever inserted for a given module.
• It properly parses relative module identifiers, instead of always taking them to be relative to the main module.
• It has a strong focus on guiding its users toward the pit of success, for example using ECMAScript 5 features to provide a secure environment and validating arguments passed to it in order to fail fast if used incorrectly.
• Attempts were made to produce highly readable and commented code explaining the more tricky subtleties of module-loading, so that others can read, understand, and use Noble Modules with confidence.

For those familiar with the intricacies of writing a JavaScript module system, the following points will also be of interest:

• It uses module.provide to give the module loading system, or any of its provider plug-ins, a chance to provide dependencies even to modules memoized with require.memoize. (This is to fix a recently-discovered hole in the specification.)
• It follows the spec more strictly than other implementations; for example module.load does not memoize the module (making it easier to use or override when writing module provider plug-ins), and require.memoize throws an error if the module is already provided.

About Us

NobleJS is a team of JavaScript programmers working on the desktop eReader team at Barnesandnoble.com. We get to work on a large desktop application, built entirely in HTML5 and running inside a custom WebKit shell. If you like what you see, we'd love to have you join us so we can continue building a great team of top-class HTML5 application developers. And keep an eye out as we move more and more of our stuff onto GitHub!

The primary contributors to Noble Modules are Paul Bouzakis and Domenic Denicola. Special thanks goes out to Donavon West (development manager), for his support and enthusiasm as we hacked away at producing a robust JavaScript module system we could use to build our product.