proxy.set.1.js

var target = { id: "id-0" };
var handler = { 
  set: function (target, property, value, receiver) {
    if (property.charAt(0) === "_") return false;
    target[property] = value;
    return true;
  }
};

var proxy = new Proxy(target, handler);

proxy.id = "value-1";
proxy._id = "value-2";

console.log(proxy); // { id: "value-1" }