使用Expo构建应用时Redux reducer参数错误排查求助

问题描述 #

遇到错误：

Error: "reducer" is a required argument, and must be a function or an object of functions that can be passed to combineReducers, js engine: hermes

使用combineReducers整合reducer，再通过configureStore创建store（替代已弃用的createStore），相关代码如下：

rootReducer文件 #

import { combineReducers } from "@reduxjs/toolkit";
import { commentReducer } from "./commentReducer.js";
import { lessonReducer } from "./lessonReducer.js";
import { studentReducer } from "./studentReducer.js";
import { subjectReducer } from "./subjectReducer.js";
import { tokenReducer } from "./tokenReducer.js";
import { userReducer } from "./userReducer.js";

export const rootReducer = combineReducers({
  user: userReducer,
  token: tokenReducer,
  subject: subjectReducer,
  student: studentReducer,
  lesson: lessonReducer,
  comment: commentReducer,
});

创建store的代码 #

import { configureStore } from "@reduxjs/toolkit";
import rootReducer from "./reducers/rootReducer.js";

const store = configureStore({
  reducer: rootReducer,
});

export default store;

单个reducer示例（所有reducer结构一致） #

import * as types from "../actions/types";

const initialState = {
  token: "",
  loading: false,
  error: null,
};

export const tokenReducer = (state = initialState, action) => {
  switch (action.type) {
    case types.LOGIN_REQUEST:
      return { ...state, loading: true, error: null };

    case types.LOGIN_SUCCESS:
      return { ...state, loading: false, token: action.payload, error: null };

    case types.LOGIN_FAILURE:
      return { ...state, loading: false, error: action.payload, token: "" };

    default:
      return state;
  }
};

尝试注释所有reducer文件后仍报错，求解决方法。

解决步骤 #

• 检查导出导入匹配性：确保每个reducer文件用export const xxxReducer命名导出，rootReducer里用import { xxxReducer }对应导入。若某个reducer用了export default，导入时要改成import xxxReducer from './xxx.js'，否则会导入undefined导致combineReducers失效。
• 校验文件路径：确认所有reducer的导入路径无拼写错误，注意文件名大小写（部分系统区分大小写），避免路径错误导致导入失败。
• 排查循环依赖：检查是否存在循环导入（比如reducer导入action，action又导入store/rootReducer），循环依赖会导致模块未初始化完成，出现undefined。
• 清除缓存重启：执行expo start -c清除Expo缓存，再重新启动项目，避免旧缓存代码残留引发问题。
• 逐步定位问题reducer：临时简化store配置，比如直接在configureStore里只传入一个确定正常的reducer（如reducer: { token: tokenReducer }），若不再报错，再逐个添加其他reducer，定位出异常文件。

内容的提问来源于stack exchange，提问作者Zerkley