<div id="app">
    <span v-if="isUser">
      <label for="username">用户账号</label>
      <input type="text" id="username" placeholder="用户账号">
    </span>
 
    <span v-else>
      <label for="email">用户邮箱</label>
      <input type="text" id="email" placeholder="用户邮箱">
    </span>
    <button @click="isUser = !isUser">切换类型</button>
  </div>