SOURCE

class Vue{
    constructor({el,data={}}={}){
        this.element = document.querySelector(el);
        this.data = new Proxy({},this.proxySetter);
        return this;
    }

    proxySetter(){
        return {
            set:function(target,key,value){
                console.log(`target key ${key} is set to ${value}`);
            },
            get:function(target,key){
                return target[key];
            }
        }
    }
}

let vue = new Vue({
    el:'#app',
    data:{
        name:'zhangsan'
    }
});
console.log(vue.data.name);

<div id="app">
    <div class="row">
        name:<input type="text" v-model="name">
    </div>
</div>