vue.html

<script src="https://cdn.jsdelivr.net/npm/vue@2.7.8/dist/vue.js"></script>


<div id="app">
    {{ message }}
    {{ counter }}
    <button v-on:click="counter++"> Click </button>
    <button v-on:click="eita"> Eita </button>
</div>

<script>
 new Vue({
     el: '#app',
     methods: {
         eita() {
             alert("eita");
         }
     },
     data: {
         counter: 0,
         message: 'Hello Vue.js!'
     }
 })
</script>