SOURCE

new Vue({
  el: '#root',
  data: {
    show: false
  }
})

<div id="root">
  <transition>
    <h1 v-show="show">hello world</h1>
  </transition>
  <button @click="show = !show">toggle</button>
</div>

@keyframes bounce-in {
  0% {
    transform:scale(0);
  }
  50% {
    transform:scale(1.5);
  }
  100% {
    transform:scale(1);
  }
}

.v-enter-active {
  animation:bounce-in 1s;
}
.v-leave-active {
  animation:bounce-in 1s reverse;
}