vue transtion 实现分析

这是我用js和css3，实现的vue transition组件相同的效果
核心js

 var btn = document.getElementById('btn');
  var box = null
  btn.addEventListener('click', function() {
    if (box) return
    box = document.createElement('div')
    box.innerText = 'box'
    box.classList = 'box v-enter v-enter-active'
    document.body.appendChild(box)
    // 必须用setTimeout
    setTimeout(() => {
      box.classList.remove('v-enter')
    })
    box.addEventListener("webkitTransitionEnd", function() {
      if (!box) return
      if (box.classList.contains('v-leave-active')) {
        box.parentNode.removeChild(box)
        box = null
      }else {
        box.classList.remove('v-enter-active')
      }
      console.log("动画结束");
    })
  }, false)

  var leaveBtn = document.getElementById('leaveBtn');
  leaveBtn.addEventListener('click', function() {
    if (!box)return
    box.classList.add('v-leave-to', 'v-leave-active')
  },false)

全部代码

<!doctype html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport"
        content="width=device-width, user-scalable=no, initial-scale=1.0, maximum-scale=1.0, minimum-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <title>Document</title>
  <style>
    *{
      padding:0;margin:0;
      box-sizing:border-box;
    }
    .box{
      width:100px;
      height:100px;
      border: 1px solid red;
      margin: 0 auto;
    }
    .v-enter{
      opacity: 0;
      transform: translate3d(-100px, 0, 0)
    }
    .v-enter-active{
      transition: all .8s;
    }
    .v-leave-to{
      opacity: 0;
      transform: translate3d(-100px, 0, 0)
    }
    .v-leave-active{
      transition: all .8s;
    }
    .page{
      position: absolute;
      left:0;
      top:0;
      bottom:0;
      right:0;
    }
  </style>
</head>
<body>

  <div style="text-align:center; margin: 30px;">
    <button id="btn">进入</button>
    <button id="leaveBtn">离开</button>
  </div>
  <script type="text/javascript">
  var btn = document.getElementById('btn');
  var box = null
  btn.addEventListener('click', function() {
    if (box) return
    box = document.createElement('div')
    box.innerText = 'box'
    box.classList = 'box v-enter v-enter-active'
    document.body.appendChild(box)
    // 必须用setTimeout
    setTimeout(() => {
      box.classList.remove('v-enter')
    })
    box.addEventListener("webkitTransitionEnd", function() {
      if (!box) return
      if (box.classList.contains('v-leave-active')) {
        box.parentNode.removeChild(box)
        box = null
      }else {
        box.classList.remove('v-enter-active')
      }
      console.log("动画结束");
    })
  }, false)

  var leaveBtn = document.getElementById('leaveBtn');
  leaveBtn.addEventListener('click', function() {
    if (!box)return
    box.classList.add('v-leave-to', 'v-leave-active')
  },false)
  </script>

</body>
</html>