javascript - 重新定义类的方法时无法访问私有(private)成员

Question

当使用#定义一个私有(private)成员，然后重新定义某个使用这个私有(private)成员的成员时，你会发现不能再使用了:

class Foo {
    #secret = "Keyboard Cat";
    
    method() {
        console.log(this.#secret);
    }
}

const target = Foo.prototype;
const key = "method";

const desc = Object.getOwnPropertyDescriptor(target, key);

const og = desc.value;

desc.value = function (...args) {
    return og.apply(target, args);
};

Object.defineProperty(target, key, desc);

new Foo().method();

Uncaught TypeError: Cannot read private member #secret from an object whose class did not declare it

为什么？在这种情况下，我所做的就是围绕原始方法。请注意，此示例是在 TypeScript 中使用装饰器的显着简化。我怎样才能解决这个问题，同时仍然能够重新定义和“更改”方法？

---

这是同样的事情，但使用了 TypeScript 装饰器:

const Curse: MethodDecorator = (target, _, desc) => {
    const og = desc.value as Function;

    desc.value = function (...args: any[]) {
        return og.apply(target, args);
    } as any;

    return desc;
};

class Foo {
    #secret = "Keyboard Cat";
    
    @Curse
    method() {
        console.log(this.#secret);
    }
}

new Foo().method();

Playground

Answer 1

您犯的错误是将方法应用于目标，即Foo.prototype，而不是通过以下方式应用于new Foo实例this 关键字:

class Foo {
    #secret = "Keyboard Cat";
    
    method() {
        console.log(this.#secret);
    }
}

const target = Foo.prototype;
const key = "method";

const desc = Object.getOwnPropertyDescriptor(target, key);

const orig = desc.value;

desc.value = function (...args) {
    return orig.apply(this, args);
//                    ^^^^
};

Object.defineProperty(target, key, desc);

new Foo().method();

Foo.prototype 没有 #secret 私有(private)字段。你会得到同样的错误

class Foo {
    #secret = "Keyboard Cat";
    
    method() {
        console.log(this.#secret);
    }
}

Foo.prototype.method();