SOURCE

var vm = new Vue({
  el: '#app',
  data: {
    cnt: []
  },
  methods: {
  	calc() {
      alert("result is " +2+3);
    },	
    foo() {
    
  	}
	}
})

<div id="app" style="font-size:12px; color:gray">
  <!-- <ul>
    <li v-for='c in cnt'>{{c}} </li>
  </ul> -->
  <button v-on:click="calc">CACL NOW</button>
</div>