效果：

Hello Jack !

<div id="app2">
    <say-hello></say-hello>
    <my-name :name="username"></my-name>
</div>
<script>
    Vue.component("sayHello",{
        template:"<h2>Hello ${this.$parent.username} !</h2>",    //访问父实例(app2)数据this.$parent
        delimiters:['${',"}"]  //修改插值语法delimiters
    });

    var app2 = new Vue({
        el:"#app2",
        data:{
            month:"September",
            username:"Lily"
        },
        components:{
            "myName":{
                template:`<div><p>My name is {{ name }} !
                          This month is {{ this.$parent.month }} .</p>
                          <button @click="changeName">changeName</button></div>`, //访问父实例(app2)数据this.$parent
                props:["name"],
                methods:{
                    changeName:function () {
                        this.$parent.username = "Jack";
                    }
                }
            }
        }
    });
</script>