CommonJS support allows you to use CommonJS notation inside map and reduce functions, but only of libraries that are stored inside the views part of the design doc.

So you could continue to access CommonJS code in design_doc.foo, from your list functions etc, but we'd add the ability to require CommonJS modules within map and reduce, but only from design_doc.views.lib.

There's no worry here about namespace collisions, as Couch just plucks views.*.map and views.*.reduce out of the design doc. So you could have a view called lib if you wanted, and still have CommonJS stored in views.lib.sha1 and views.lib.stemmer if you wanted.

The implementation is simplified by enforcing that CommonJS modules to be used in map functions be stored in views.lib.

A sample design doc (taken from the test suite in Futon) is below:

{
   "views" : {
      "lib" : {
         "baz" : "exports.baz = 'bam';",
         "foo" : {
            "zoom" : "exports.zoom = 'yeah';",
            "boom" : "exports.boom = 'ok';",
            "foo" : "exports.foo = 'bar';"
         }
      },
      "commonjs" : {
         "map" : "function(doc) { emit(null, require('views/lib/foo/boom').boom)}"
      }
   },
   "_id" : "_design/test"
}

The require() statement is relative to the design document, but anything loaded form outside of views/lib will fail.