const moduleA = {
 state: { ... },
 mutations: { ... },
 actions: { ... },
 getters: { ... }
}

const moduleB = {
 state: { ... },
 mutations: { ... },
 actions: { ... }
}

const store = new Vuex.Store({
 modules: {
 a: moduleA,
 b: moduleB
 }
})

store.state.a // -> moduleA's state
store.state.b // -> moduleB's state

const moduleA = {
 state: { count: 0 },
 mutations: {
 increment: (state) {
  // state 是模块本地的状态。
  state.count++
 }
 },

 getters: {
 doubleCount (state) {
  return state.count * 2
 }
 }
}

const moduleA = {
 // ...
 actions: {
 incrementIfOdd ({ state, commit }) {
  if (state.count % 2 === 1) {
  commit('increment')
  }
 }
 }
}

const moduleA = {
 // ...
 getters: {
 sumWithRootCount (state, getters, rootState) {
  return state.count + rootState.count
 }
 }
}

// types.js

// 定义 getter、 action 和 mutation 的常量名称
// 并且在模块名称上加上 `todos` 前缀 
export const DONE_COUNT = 'todos/DONE_COUNT'
export const FETCH_ALL = 'todos/FETCH_ALL'
export const TOGGLE_DONE = 'todos/TOGGLE_DONE'
// modules/todos.js
import * as types from '../types'

// 用带前缀的名称来定义 getters, actions and mutations 
const todosModule = {
 state: { todos: [] },

 getters: {
 [types.DONE_COUNT] (state) {
  // ...
 }
 },

 actions: {
 [types.FETCH_ALL] (context, payload) {
  // ...
 }
 },

 mutations: {
 [types.TOGGLE_DONE] (state, payload) {
  // ...
 }
 }
}

store.registerModule('myModule', {
 // ...
})

const myPlugin = store => {
 // 当 store 在被初始化完成时被调用
 store.subscribe((mutation, state) => {
 // mutation 之后被调用
 // mutation 的格式为 {type, payload}。
 })
}

const store = new Vuex.Store({
 // ...
 plugins: [myPlugin]
})

export default function createWebSocketPlugin (socket) {
 return store => {
 socket.on('data', data => {
  store.commit('receiveData', data)
 })
 store.subscribe(mutation => {
  if (mutation.type === 'UPDATE_DATA') {
  socket.emit('update', mutation.payload)
  }
 })
 }
}

const plugin = createWebSocketPlugin(socket)

const store = new Vuex.Store({
 state,
 mutations,
 plugins: [plugin]
})

const myPluginWithSnapshot = store => {
 let prevState = _.cloneDeep(store.state)
 store.subscribe((mutation, state) => {
 let nextState = _.cloneDeep(state)

 // 对比 prevState 和 nextState...

 // 保存状态，用于下一次 mutation
 prevState = nextState
 })
}

const store = new Vuex.Store({
 // ...
 plugins: process.env.NODE_ENV !== 'production'
 ? [myPluginWithSnapshot]
 : []
})

import createLogger from 'vuex/dist/logger'

const store = new Vuex.Store({
 plugins: [createLogger()]
})

const logger = createLogger({
 collapsed: false, // 自动展开记录 mutation
 transformer (state) {
 // 在记录之前前进行转换
 // 例如，只返回指定的子树
 return state.subTree
 },
 mutationTransformer (mutation) {
 // mutation 格式 { type, payload }
 // 我们可以按照想要的方式进行格式化
 return mutation.type
 }
})

const store = new Vuex.Store({
 // ...
 strict: true
})

const store = new Vuex.Store({
 // ...
 strict: process.env.NODE_ENV !== 'production'
})