SOURCE

new Vue({
  el: '#root',
  data: {
    show: true
  },
  methods:{
    handleBeforeEnter(el) {
      el.style.opacity = 0
    },
    handleEnter(el, done) {
      Velocity(el,{
        opacity:1
      },{
        duration:1000,
        complete:done
      })
    },
    handleAfterEnter(el) {
      console.log('动画结束')
    }
  }
})

<div id="root">
  <transition
     @before-enter="handleBeforeEnter"  
     @enter="handleEnter" 
     @after-enter="handleAfterEnter" 
  >
    <h1 v-show="show">hello world</h1>
  </transition>
  <button @click="show = !show">toggle</button>
</div>