Edit in JSFiddle

<div id="app">
  <select v-model="selected">
    <option disabled value="">-</option>
    <option>PHP</option>
    <option>JavaScript</option>
    <option>Java</option>
</select>
<p>選択: {{ selected }}</p>
</div>
<script src="https://cdn.jsdelivr.net/npm/vue/dist/vue.js"></script>
var app = new Vue({
  el: '#app',
  data: {
    selected: ""
  }
})