Redux中单个reducer能否同时修改自身及其他多个reducer的状态

完全可以实现，常用有3种符合Redux设计规范的实现方式：

• 方案1：让reducer1、reducer2主动响应目标action
  这个是最推荐的实现方式。Redux中不存在「某个action专属特定reducer」的规则，所有分发的action会传递给所有reducer，你只需要在reducer1、reducer2的逻辑中新增对reducer3对应action类型的处理即可。
  示例代码：

// reducer1 新增对应处理分支
const reducer1 = (state = initialState1, action) => {
  switch(action.type) {
    // 原有reducer1的业务逻辑
    case 'R1_UPDATE_FIELD':
      return {...state, field1: action.payload}
    // 新增对reducer3触发的action的处理
    case 'R3_TRIGGER_GLOBAL_UPDATE':
      return {...state, field2: action.payload.r1NewValue}
    default:
      return state
  }
}

// reducer2 同理新增处理分支
const reducer2 = (state = initialState2, action) => {
  switch(action.type) {
    case 'R3_TRIGGER_GLOBAL_UPDATE':
      return {...state, fieldX: action.payload.r2NewValue}
    default:
      return state
  }
}

// reducer3的原有逻辑不变，还是正常处理该action修改自身状态
const reducer3 = (state = initialState3, action) => {
  switch(action.type) {
    case 'R3_TRIGGER_GLOBAL_UPDATE':
      return {...state, ownField: action.payload.r3Value}
    default:
      return state
  }
}

这种方式完全符合Redux的单向数据流设计，不需要修改整体的reducer组合逻辑，改造成本最低。

• 方案2：自定义根reducer，替代默认的combineReducers
  如果你使用combineReducers来组合各个子reducer，默认每个子reducer只能拿到自己对应的状态切片，无法修改其他切片。你可以自己实现根reducer，拿到完整的全局状态，当识别到reducer3的目标action时，直接修改所有相关的状态切片即可。
  示例代码：

const rootReducer = (state = {}, action) => {
  // 处理需要跨切片更新的action
  if (action.type === 'R3_TRIGGER_GLOBAL_UPDATE') {
    return {
      reducer1: {...state.reducer1, field2: action.payload.r1NewValue},
      reducer2: {...state.reducer2, fieldX: action.payload.r2NewValue},
      reducer3: {...state.reducer3, ownField: action.payload.r3Value}
    }
  }
  // 其他action还是走原有子reducer的逻辑，和combineReducers效果一致
  return {
    reducer1: reducer1(state.reducer1, action),
    reducer2: reducer2(state.reducer2, action),
    reducer3: reducer3(state.reducer3, action)
  }
}

• 方案3：使用Redux Toolkit的监听中间件做联动
  如果你使用Redux Toolkit开发，可以引入createListenerMiddleware监听reducer3的目标action，触发后主动分发修改reducer1、reducer2的action。这种方式适合跨切片逻辑比较复杂、需要做额外副作用处理的场景。
  示例代码：

import { createListenerMiddleware } from '@reduxjs/toolkit'

const listenerMiddleware = createListenerMiddleware()
// 添加监听器
listenerMiddleware.startListening({
  actionCreator: r3TriggerUpdateAction, // 就是reducer3对应的action创建函数
  effect: async (action, listenerApi) => {
    // 分发修改reducer1和reducer2的action
    listenerApi.dispatch(updateR1Field(action.payload.r1NewValue))
    listenerApi.dispatch(updateR2Field(action.payload.r2NewValue))
  }
})

内容的提问来源于stack exchange，提问作者Rishabh Jain