Support private fields in class instances #10
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When creating a proxy for an instance of a class, ensure that if a
method forwarded to the instance can access private fields within that
class. For instance:
``` javascript
class Foo {
#qux;
bar() {
this.#qux = true;
return this.#baz();
}
#baz() {
return [this.#qux, 42];
}
}
const foo = new Foo();
const proxy = createSwappableProxy(foo);
proxy.bar();
```
As it stands, this produces the TypeError:
Cannot write private member #qux to an object whose class did not declare it
If we call `this.#baz()` before we set `#qux`, then we get:
Receiver must be an instance of class Foo
We get this error because `proxy.bar` returns a function that is bound
to the proxy object and not our Foo object. Therefore, if we are know we
are trying to access a method on Foo we need to get the proxy to return
a wrapper function which ensures that when the method is called, it is
done so with our Foo instance as `this` and not the proxy object. This
is explained here in the MDN docs:
<https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#no_private_property_forwarding>
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When creating a proxy for an instance of a class, ensure that if a method forwarded to the instance can access private fields within that class. For instance:
As it stands, this produces the TypeError:
If we call
this.#baz()before we set#qux, then we get:We get this error because
proxy.barreturns a function that is bound to the proxy object and not our Foo object. Therefore, if we are know we are trying to access a method on Foo we need to get the proxy to return a wrapper function which ensures that when the method is called, it is done so with our Foo instance asthisand not the proxy object. This is explained here in the MDN docs:https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Proxy#no_private_property_forwarding
Fixes #2.