reatividade.html

<script src="https://unpkg.com/vue"></script>

<div id="app">
    <h1>{{ count }}</h1>
    <button v-on:click="increment()">Add one</button>
</div>

<script>
    new Vue({
        el: '#app',

        data: {
            count: 0
        },

        methods: {
            increment(){
                this.count += 1
            }
        },
    });
</script>