code: function generatedReducer(state = fn.defaultState, action) {
        const builtinState = builtinReducer(state, action, page);
        if (builtinState) return builtinState;
        if (Object.hasOwnProperty.call(fn, action.type) && typeof fn[action.type] === 'function') {
          return produce(state, (draft) => {
            try {
              return fn[action.type](draft, action);
            } catch (e) {
              if (process.env.NODE_ENV !== 'production') {
                throw e;
              }
              console.error('It"s called by rrc-loader-helper:' + e);
              sendError(e);
              return state;
            }
          });
        }
        return state;
      }
docs: reducer 为对象的时候包装为immer处理方式
  对象内 defaultState 为必须属性