<template>
  <div>
    <button v-on:click="show = !show">
      Toggle
    </button>
    <transition name="fade">
      <p v-if="show">hello</p>
    </transition>
  </div>
</template>
<script>
  export default {
    data: function() {
      return {
        show: true
      }
    }
  }
</script>
<style>
  .fade-enter-active,
  .fade-leave-active {
    transition: opacity .5s
  }
  
  .fade-enter,
  .fade-leave-to {
    opacity: 0
  }
</style>