created () {
 let text = Array(1000000).fill('xxx').join(',') //创建一个大的字符串用于验证内存占用
 $eventBus.$on('home-on', (...args) => {
  this.text = text
 })
 },
 mounted () {
 setTimeout(() => {
  $eventBus.$emit('home-on', '这是home $emit参数', 'ee')
 }, 1000)
 },
 beforeDestroy () {
 // 注意这里没有off掉'home-on'的订阅事件
 }
 // eventBus是全局的

 created () {
 let text = Array(1000000).fill('xxx').join(',') //创建一个大的字符串用于验证内存占用
 $eventBus.$on('home-on', (...args) => {
  this.text = text
 })
 },
 mounted () {
 setTimeout(() => {
  $eventBus.$emit('home-on', '这是home $emit参数', 'ee')
 }, 1000)
 },
 beforeDestroy () {
 $eventBus.$off('home-on') // 注意这里off掉了'home-on'的订阅事件
 }
 // eventBus是全局的

class EventBus {
 constructor (vue) {
 if (!this.handles) {
  Object.defineProperty(this, 'handles', {
  value: {},
  enumerable: false
  })
 }
 this.Vue = vue
 this.eventMapUid = {} // _uid和EventName的映射
 }
 setEventMapUid (uid, eventName) {
 if (!this.eventMapUid[uid]) this.eventMapUid[uid] = []
 this.eventMapUid[uid].push(eventName) // 把每个_uid订阅的事件名字push到各自uid所属的数组里
 }
 $on (eventName, callback, vm) { // vm是在组件内部使用时组件当前的this用于取_uid
 if (!this.handles[eventName]) this.handles[eventName] = []
 this.handles[eventName].push(callback)
 if (vm instanceof this.Vue) this.setEventMapUid(vm._uid, eventName)
 }
 $emit () {
 // console.log('EventBus emit eventName===', eventName)
 let args = [...arguments]
 let eventName = args[0]
 let params = args.slice(1)
 if (this.handles[eventName]) {
  let len = this.handles[eventName].length
  for (let i = 0; i < len; i++) {
  this.handles[eventName][i](...params)
  }
 }
 }
 $offVmEvent (uid) {
 let currentEvents = this.eventMapUid[uid] || []
 currentEvents.forEach(event => {
  this.$off(event)
 })
 }
 $off (eventName) {
 delete this.handles[eventName]
 }
}
// 下面写成Vue插件形式，直接引入然后Vue.use($EventBus)进行使用
let $EventBus = {}
$EventBus.install = (Vue, option) => {
 Vue.prototype.$eventBus = new EventBus(Vue)
 Vue.mixin({
 beforeDestroy () {
  this.$eventBus.$offVmEvent(this._uid) // 拦截beforeDestroy钩子自动销毁自身所有订阅的事件
 }
 })
}
export default $EventBus

// main.js中
...
import EventBus from './eventBus.js'
Vue.use(EnemtBus)
...

 created () {
 let text = Array(1000000).fill('xxx').join(',')
 this.$eventBus.$on('home-on', (...args) => {
  console.log('home $on====>', ...args)
  this.text = text
 }, this) // 注意第三个参数需要传当前组件的this，如果不传则需要手动销毁
 },
 mounted () {
 setTimeout(() => {
  this.$eventBus.$emit('home-on', '这是home $emit参数', 'ee')
 }, 1000)
 },
 beforeDestroy () {
 // 这里就不需要手动的off销毁eventBus订阅的事件了
 }