vue half animation (click - from top to bottom disappeared, disappeared from top to bottom)

<template>
  <div id="bigData" ref="bigData">
    <button @click="flag=!flag">按钮</button>
    <transition @before-enter="beforeEnter" @enter="enter" @after-enter="afterEnter">
      <div class="ball" v-show="flag"></div>
    </transition>
  </div>
</template>

<script>
export default {
  data() {
    return {
      flag: false
    };
  },
  methods: {
    beforeEnter(el) {
      el.style.transform = "translate(0,0)";
    },
    enter(el,done) {
      el.offsetWidth;//这句话没有实际的作用，如果不写 没有动画效果
      el.style.transform = "translate(150px,450px)";
      el.style.transition = "all 1s ease";
      done();//就是 afterEnter引用 
    },
    afterEnter(el) {
      this.flag=!this.flag;
    }
  }
};
</script>

<style>
.ball {
  width: 20px;
  height: 20px;
  background-color: red;
  border-radius: 50%;
}
</style>