code: function(defaultConfig, fileConfig, envConfig, argConfig) {
      var mergedConfig = _.merge({}, defaultConfig, fileConfig, envConfig, argConfig);
  
      for(var prop in mergedConfig) {
          this[prop] = mergedConfig[prop];
      }
  
      Object.defineProperties(this, {
          "_default": {
              value: defaultConfig,
              enumerable: false
          },
          "_file": {
              value: fileConfig,
              enumerable: false
          },
          "_env": {
              value: envConfig,
              enumerable: false
          },
          "_arg": {
              value: argConfig,
              enumerable: false
          }
      });
  }
docs: Config class