code: function(parentId, moduleName) {
      moduleName = normalizeModule(parentId, moduleName);
  
      var module = define.modules[moduleName];
      if (!module) {
          module = define.payloads[moduleName];
          if (typeof module === 'function') {
              var exports = {};
              var mod = {
                  id: moduleName,
                  uri: '',
                  exports: exports,
                  packaged: true
              };
  
              var req = function(module, callback) {
                  return _require(moduleName, module, callback);
              };
  
              var returnValue = module(req, exports, mod);
              exports = returnValue || mod.exports;
              define.modules[moduleName] = exports;
              delete define.payloads[moduleName];
          }
          module = define.modules[moduleName] = exports || module;
      }
      return module;
  }
docs: Internal function to lookup moduleNames and resolve them by calling the
  definition function if needed.