es6 添加事件監聽

//定義被偵聽的目標對象
var engineer = { name: 'Joe Sixpack', salary: 50 };

//定義處理程序
var interceptor = {
    set: function (receiver, property, value) {
        console.log(property, 'is changed to', value);
        receiver[property] = value;
    }
};

//創建代理以進行偵聽
new Proxy(engineer, interceptor);
//做一些改動來觸發代理
engineer.salary = 60;//控制台輸出：salary is changed to 60
engineer.salary = 50;//控制台輸出：salary is changed to 60