劫持 .proto

Question

对象实例化时，无论是string/function/etc，还是__proto__属性。属性似乎是由 Object.prototype 中的 __proto__ 访问器生成的...

Object.prototype == {
    __defineGetter__    : __defineGetter__()
    __defineSetter__    : __defineSetter__()
    __lookupGetter__    : __lookupGetter__()
    __lookupSetter__    : __lookupSetter__()
    constructor         : Object()
    hasOwnProperty      : hasOwnProperty()
    isPrototypeOf       : isPrototypeOf()
    propertyIsEnumerable: propertyIsEnumerable()
    toLocaleString      : toLocaleString()
    toString            : toString()
    valueOf             : valueOf()
    get __proto__       : __proto__()               //  getter
    set __proto__       : __proto__()               //  setter
};

我想知道是否可以劫持此 __proto__ 属性以在实例化对象时执行代码块。想法是用自定义属性替换 __proto__ 属性，在调用原始访问器以在新实例上创建 __proto__ 之前执行一些代码。

如果有道理！如果不是，这就是我要做的：

pro = Object.prototype;
tmp = {};
Object.defineProperty(tmp, '__proto__',
    Object.getOwnPropertyDescriptor(pro, '__proto__')
);
delete pro.__proto__;
Object.defineProperty(pro, '__proto__',{
    get:function(){
        console.warn('intercepted Get __proto__');
        return tmp.__proto__;
    },
    set(p){
        console.warn('intercepted Set __proto__');
        tmp.__proto__ = p;
    }
});

尚不能确定它是否正常工作，但这只是一个示例，旨在向您展示我正在努力实现的目标。

Answer 1

I'm wondering if it is possible to hijack this __proto__ property to execute a code block when an object is instantiated.

没有。 __proto__ 属性的访问器在创建对象时不会被调用。它们仅在您获取或设置 __proto__ 时被调用。您可以通过查看 the spec:

查看创建对象时发生的情况

ObjectCreate (proto [ , internalSlotsList ])

The abstract operation ObjectCreate with argument proto (an object or null) is used to specify the runtime creation of new ordinary objects. The optional argument internalSlotsList is a List of the names of additional internal slots that must be defined as part of the object. If the list is not provided, a new empty List is used. This abstract operation performs the following steps:

If internalSlotsList was not provided, let internalSlotsList be a new empty List.

Let obj be a newly created object with an internal slot for each name in internalSlotsList.

Set obj's essential internal methods to the default ordinary object definitions specified in 9.1.

Set the [[Prototype]] internal slot of obj to proto.

Set the [[Extensible]] internal slot of obj to true.

Return obj.

回想一下 __proto__ 不是对象的原型引用；那是对象中的 [[Prototype]] 槽，它在代码中不可访问。 __proto__ 只是一种（仅限网络）访问该插槽中的值的方法。（在 Object 和 Reflect 上的 getPrototypeOf / setPrototypeOf 是 __proto__ 官方不支持的通用方式并非所有对象都有 __proto__ 因为并非所有对象都继承自 Object.prototype:

var o1 = {};
console.log("__proto__" in o1); // true
var o2 = Object.create(null);   // No prototype
console.log("__proto__" in o2); // false
var o3 = Object.create(o2);     // Has a prototype, but still no link to Object.prototype
console.log("__proto__" in o3); // false

劫持 .proto

Hijacking .proto

javascript

inheritance

prototype

proto

劫持 .__proto__

Hijacking .__proto__

javascript

inheritance

prototype

proto

劫持 .proto

Hijacking .proto