SOURCE

var app = new Vue({
    el:'#app',
    data:{
        num:1
    },
    methods:{
        add:function(){
            return this.num++;
        }
    }
});
app.$on('reduce',function(){
    console.log('执行了reduce方法')
    this.num--;
});
app.$once('reduceOnce',function(){
    console.log("只执行一次的方法");
    this.num--;
})
var reduce = ()=>{
    app.$emit("reduce");
}
var reduceOnce = ()=>{
    app.$emit("reduceOnce");
}
//关闭事件
function off(){
    app.$off('reduce');
}

<script src="https://unpkg.com/vue"></script>
<script src="http://code.jquery.com/jquery-3.3.1.js" integrity="sha256-2Kok7MbOyxpgUVvAk/HJ2jigOSYS2auK4Pfzbm7uH60=" crossorigin="anonymous"></script>
<h1>实例事件</h1>
<hr />
<div id="app">
    <p>{{num}}</p>
    <button @click="add">add</button>
</div>
<button onclick="reduce()">reduce</button>
<button onclick="reduceOnce()">reduceOnce</button>
<button onclick="off()">off</button>

*:not(button){
    color:#fff;
}
a:visited{
    color:lightblue
}