Vue过渡组件transition淡入

<transition name="fade">
  <router-view v-if="isShow"></router-view>
</transition>

一定要在mounted中改变isShow，在created中无效

mounted () {
  this.isShow = true;
},

  .fade-enter-active, .fade-leave-active {
    transition: opacity 1s;
  }
  .fade-enter, .fade-leave-to {
    opacity: 0;
  }