// 单个元素
  <transition name="自定义名字">
   <p v-if="show">hello</p>
  </transition>
 // 列表元素: 注意group的直接子元素是v-for渲染出来的
  <ul class="list">
   <transition-group name="list">
    <li v-for="(item, index) in gameList" :key="item.id">
     <app-horizontal :itemData="item"></app-horizontal>
    </li>
   </transition-group>
  </ul>

 .name-enter
 {
  opacity: 0;
  transform: translateY(30px)
 }

 .name-enter-active {
  transition: all .3s;
 }

 .name-enter-to {
  opacity: 1;
  transform: translateY(0);
 }

 .name-enter-active:nth-child(3n+1) {
  transition-delay: 0s;
 }
 .name-enter-active:nth-child(3n+2) {
  transition-delay: .1s;
 }
 .name-enter-active:nth-child(3n+3) {
  transition-delay: .2s;
 }

// 例如实现上述列表依次显示
 <ul class="list">
  <transition-group
   v-bind:css="false"
   v-on:before-enter="beforeEnter"
   v-on:enter="enter"
   v-on:after-enter="afterEnter">
   <li v-for="(item, index) in gameList" 
    :key="item.id" 
    :data-delay="index*100" 
   >
     <app-horizontal :itemData="item"></app-horizontal>
   </li>
  </transition-group>
 </ul> 
 // 
 methods: {
  // 事先定义上述类名
  // 在beforeEnter enter afterEnter 钩子中手动操作上述类名
  
  // 初始态
  beforeEnter(dom) {
   dom.classList.add('list-enter', 'list-enter-active');
  },
  // 中间态
  enter(dom,done) {
   // 通过 setTimeout + dataset 实现过渡
   let delay = dom.dataset.delay;
   setTimeout(function () {
    dom.classList.remove('list-enter');
    dom.classList.add('list-enter-to');
    //监听 transitionend 事件
    var transitionend = window.ontransitionend "transitionend" : "webkitTransitionEnd";
    dom.addEventListener(transitionend, function onEnd() {
     // 移除事件
     dom.removeEventListener(transitionend, onEnd);
     //调用done(),表示动画已完成
     done()
    });
   }, delay)
  },
  // 终止态
  afterEnter(dom) {
   dom.classList.remove('list-enter-to', 'list-enter-active');
  }
 }

<ul class="list">
  <transition-group
   v-bind:css="false"
   v-on:before-enter="beforeEnter"
   v-on:enter="enter"
   v-on:after-enter="afterEnter">
   <li v-for="(item, index) in gameList" 
    :key="item.id" 
    :data-delay="index*100"
    data-y = "100%" 
   >
     <app-horizontal :itemData="item"></app-horizontal>
   </li>
  </transition-group>
 </ul> 
 // 对应的操作方法; 添加自定义的 dataset,给dom设置css样式;根据需求添加
  methods: {
   // 初始态
  beforeEnter(dom) {
   let { x = 0, y = 0, opacity = 0 } = dom.dataset;
   dom.style.cssText = `transition: .3s;opacity: ${opacity};transform: translateX(${x}) translateY(${y});`;
  },
  // 中间态
  enter(dom,done) {
   let delay = dom.dataset.delay;
   setTimeout(function () {
    dom.style.cssText = `transition: .3s;opacity: 1;transform: translateX(0) translateY(0);`;
    //监听 transitionend 事件
    var transitionend = window.ontransitionend "transitionend" : "webkitTransitionEnd";
    dom.addEventListener(transitionend, function onEnd() {
       dom.removeEventListener(transitionend, onEnd);
       done(); 
    });
   }, delay)
  },
  // 终止态
  afterEnter(dom) {
   dom.style.cssText = "";
  }
 }

webkit-animation动画有三个事件：
  开始事件: webkitAnimationStart
  结束事件: webkitAnimationEnd
  重复运动事件: webkitAnimationIteration
css3的过渡属性transition: 一个事件
  过渡结束: webkitTransitionEnd