<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
</head>

<body>
    <div id="app">
        <h2>{{counter}}</h2>
        <h2 v-on:click='increment'>+</h2>
        <h2 v-on:click='decrement'>-</h2>
    </div>
    <script src="./js/vue.js"></script>
    <script>
        const app = new Vue({
            el: '#app',
            data: {
                counter: 0
            },
            methods: {
                increment() {
                    this.counter++
                },
                decrement() {
                    this.counter--
                }
            }
        })
    </script>
</body>

</html>

运行结果