Vue 计数器

https://www.bilibili.com/video/BV12J411m7MG/?p=10

<div class="input-num">
  <button @click>-</button>
  <span>{{}}</span>
  <button @click>+</button>
</div>

var app = new Vue({
  el:"#app",
  data:{},
  methods:{}
})