vue中appear的问题

Question

<div id="app">

    <transition
        appear
        enter-active-class="animated swing"    
        leave-active-class="animated shake"
        appear-class='animated swing'
        appear-to-class='animated shake'
        appear-active-class='animated shake'
    >
        <div v-if='show'>hello world</div>
    </transition>
    <button @click='handleClick'>切换状态</button>
</div>

这样写的代码(前提条件：引用了animate.css这个库)，为啥dom节点在初始渲染的过渡效果不生效？