2012/12/13 Kevin Reid <[email protected]> > Yes, exactly. I was just this minute in the process of writing such a > proxy myself, and have not yet confirmed whether it is accepted by the > invariant checks for all the cases I'm thinking of (testing against FF > 18.0). > > Note that either > (1) all the switched-among targets need to have the same [[Prototype]], > (2) the proxy has to pretend that all inherited properties are actually > own, > (3) or mutating [[Prototype]] (i.e. __proto__) needs to be possible. > In my particular use case, (1) is not a suitable option, so I would > implement (2) if (3) is not available. Not that I approve of (3), but one > does what one must to accomplish virtualization. >
It's worth noting that direct proxies do not enforce any invariants w.r.t. inherited property access/update. For instance, the "get" trap is allowed to return arbitrary values over time for a non-configurable, non-writable *inherited* property. In other words, it's as if direct proxies always have a mutable __proto__ (even if Object.getPrototypeOf returns a stable result). Hence, (3) is the best way to rationalize the behavior of direct proxies.
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