vue.js条件渲染-用key管理可复用的元素

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<!DOCTYPE html>
<script src="https://cdn.staticfile.org/vue/2.2.2/vue.js"></script>
<html>
<head>
<meta charset="utf-8">
<title>文档标题</title>
</head>
<body>
  <div id ="app2">
    <template v-if="loginType === 'username'">
    <label>Username</label>
    <input placeholder="Enter your username" key="username-input">
    </template>
    <template v-else>
      <label>Email</label>
      <input placeholder="Enter your email address" key="email-input">
    </template>
    <button v-on:click="changeType">
      更改类型
    </button>
  </div>
  
</body>
  
</html>
HTML