new Vue({
 render: h => h(App),
 router,
 store,
 data: {
  event: new Vue()
 }
}).$mount('#app')

methods: {
   addCart (e) {
    let pos = {
     x: parseInt(e.target.getBoundingClientRect().x + 4),
     y: parseInt(e.target.getBoundingClientRect().y + 4)
    }
    this.$root.event.$emit('ballPosition', pos)
   }
  }

  created () {
   this.$root.event.$on('ballPosition', (target) => {
    this._initBall(target)
   })
  },  
 methods: {
   _initBall (target) {
    this.ball = true
    this.ballMassage = target
   }
 }

created () {
   this.$root.event.$on('ballPosition', (target) => {
    this._initBall(target)
   })
  },
  methods: {
   _initBall (el) {
    this.ball.show = true
    this.ball.el = el
   },
   beforeEnter (el) {
    let pos = this.ball.el.target.getBoundingClientRect()
    el.style.top = `${pos.y}px`
    el.style.left = `${pos.x}px`
   },
   enter (el, done) {
    // 触发动画重绘
    el.offsetHeight
    let [x, y] = [parseInt(this.$refs.cart.getBoundingClientRect().x + 4), parseInt(this.$refs.cart.getBoundingClientRect().y + 8)]
    el.style.top = `${y}px`
    el.style.left = `${x}px`
    el.style.transition = `left .1s linear, top .1s cubic-bezier(.63,.02,.96,.56)`
    done()
   },
   afterEnter () {
    this.ball.show = false
   }
  },

<template>
   <div class="components-a">
      <button @click="abtn">A按钮</button>
   </div>
</template>
<script>
import eventVue from '../../js/event.js'
export default {
   name: 'app',
   data () {
    return {
        ‘msg':"我是组件A"
    }
   },
   methods:{
      abtn:function(){
          eventVue.$emit("myFun",this.msg)  //$emit这个方法会触发一个事件
      }
   }
}
</script>

<template>
   <div class="components-a">
     <div>{{btext}}</div>
   </div>
</template>
<script>
import eventVue from '../../js/event.js'
export default {
  name: 'app',
  data () {
    return {
      'btext':"我是B组件内容"
    }
  },
  created:function(){
    this.bbtn();
  },
  methods:{
    bbtn:function(){
      eventVue.$on("myFun",(message)=>{  //这里最好用箭头函数，不然this指向有问题
         this.btext = message   
      })
    }
  }
}
</script>