SOURCE

let obj = new Proxy({},
{
  get(target, key, receiver) {
    console.log(`get ${key}`);
    return Reflect.get(target, key, receiver)
  },
  set(target, key, value, receiver) {
    console.log(`set ${key}`);
    return Reflect.set(target, key, value, receiver);
  }
});

obj.count = 1;
console.log(obj.count);

var person = {
  name: "张三"
};

var proxy = new Proxy(person, {
  get: function(target, property) {
    if (property in target) {
      return target[property];
    } else {
      throw new ReferenceError("Property \"" + property + "\" does not exist.");
    }
  }
});

proxy.name // "张三"
proxy.age // 抛出一个错误