Simple CommonJS module implementation

require.js

'use strict';

/**
 * Simple module define/require functionality
 *
 * NOTE: this is NOT requirejs
 */

var modules = {};

/**
 * Require
 *
 * var grid = require('UI.views.grid');
 */
function require(name) {
  var 

    ns = String.prototype.split.call(name, '.'),
    name,
    module = modules;

  while (name = Array.prototype.shift.call(ns)) {
    module = module[name];

    if (typeof module == 'undefined') {
      throw TypeError('module: ' + name + ' could not be found');
    }
  }

  return module;
}

/**
 * Define
 *
 * require.define('UI.views', function (module, exports, require) {
 *   exports.grid = function () {}; 
 * });
 */
 (function (require) {
  var

    copy = function (target, source, overwrite) {
      var key;
      for (key in source) {
        if (overwrite || target[key] === undefined) {
          target[key] = source[key];
        }
      }

      return target;
    },

    create = function (namespace, value) {
      var node = modules,
        ns = namespace ? String.prototype.split.call(namespace, '.') : [],
        name = null,
        nso;

      while (name = Array.prototype.shift.call(ns)) {
        nso = node[name];
        if (!nso) {
          nso = (value && ns.length === 0) ? value : {};
          node[name] = nso;
        }
        node = nso;
      }
      return node;
    };

  require.define = function (rs, fn, overwrite) {
    var 

      module = {},
      exports = {},
      ns = String.prototype.split.call(rs, '.'),
      node = modules,
      nso;

    module.exports = exports;
    fn(module, exports, require);

    copy(create(rs), module.exports, overwrite);
  };
}(require));

usage.js

// The idea is to keep extending like partials in C# instead of replacing namespace
require.define('ui.views', function (module, exports, require) {
  var models = require('models');

  exports.GridView = function () {
    this.model = models.Grid;
  };
});

require.define('ui.views', function (module, exports, require) {
  exports.CellView = function () {};
});

var views = require('ui.views');
var grid = new views.GridView;
var cell = new views.CellView;