As mentioned before, I considered renaming RunJS to RequireJS. I did the transition, and RequireJS is on GitHub. There is a conversion script that will convert CommonJS modules to the Transport/C proposal that works with RequireJS.
I have converted Raindrop to use a modified Dojo 1.4 that uses RequireJS instead of the normal Dojo loader, and all Raindrop modules are written in the Transport/C module format that RequireJS understands. Raindrop works, so the RequireJS code has been proven in a real project that has many modules with nested dependencies. The RequireJS code is already battle-tested.
I have opened a thread on the jQuery forum about using RequireJS for jQuery's require() needs. I can do a build with Dojo 1.4 that uses RequireJS, and any Dojo 2.0 effort is likely to use RequireJS as the module loader.
I believe RequireJS is the loader browser-based toolkits should use. At the very least, the module format and API supported by RequireJS should be used by browser-based toolkits, even if they want to build their own loader.
Next plans for RequireJS:
1) Contact the MooTools and Prototype folks to see if they want to use it. It allows loading code that does not export a module value, and has access to the global environment. They can use it to load code that augments native prototypes. RequireJS can load existing, plain JS files that do not define a module too.
2) Put up a web site with builds. While you can use RequireJS just from grabbing it from GitHub, it would be nice to have the builds of RequireJS with its different levels of functionality already built and easy to download.
2) Do a fork of Node that uses RequireJS on the server. I believe the async module format used by RequireJS is great fit for Node and its async goals.
3) See if I can do a fork of Narwhal to do the same thing.
I believe I can get RequireJS to work on the server and still support the existing CommonJS format when the server supports synchronous loading. By having native support in some server-based systems for RequireJS, it will be easier to share code with the browser.
To recap, my three main issues with using the existing CommonJS module spec, and why RequireJS exists:
1) So far the CommonJS group does not think the browser is common enough to qualify as a first class citizen in the module spec. The group is mainly concerned with environments outside the browser. As a result, the CommonJS module spec does not work well natively in the browser -- it either requires an XHR-based loader, which we have found to have problems in Dojo, or require a server-side transform process. A server-side transform process should not be required to do web development in the browser.
RequireJS uses a function wrapper around the module to avoid these problems and allow loading modules via script tags. Just save the file and hit reload in the browser.
2) There is a free variable, called "exports". It is an object. You cannot set the value of exports inside your module code, you can only add properties. This means for instance, your module cannot be a function. In Dijit, Dojo's widget system, all widgets are constructor functions. The "exports" restriction makes your APIs awkward if you want to export functions for module values. The claim is that this exports restriction helps with circular dependencies, but it only helps a little bit. To me, it is not worth slightly improving an edge case when it sacrifices a greater usefulness and simplicity in user's modules.
RequireJS and its format can handle circular dependencies just fine. In the format supported by RequireJS, you to define a module as a function. Although, you can still use exports as CommonJS uses it if you so desire.
3) The require.main property seems like a hack. It is normally used so that a module can say if (require.main === module.id) or if (require.main === module) then do some "main" work. The module format should just define an exports.main convention for indicating "main" functionality. It is less typing, and more robust, since different code entry points have a different idea of "main". For instance, an HTTP request handler likely has specific requirements on what it considers to be the "main". The top level entry point should decide what code to execute as "main", not logic inside the module.
RequireJS does not support the require.main idiom.
So I believe the path used by RequireJS is more robust overall, works better/scales better in the browser. However, I still want to provide enough support for the existing CommonJS modules in the meantime to allow more code sharing.
In the long run though, the CommonJS format as it exists today should be replaced with something better. It is troublesome that the CommonJS group is not really targeting the browser, but over time, the broader JS community will expect browser toolkits to support CommonJS specs. It does not seem right to end up with non-optimal solutions in the browser when the browser is the most common JS platform.