Hi, I've been working on implementing Notification proxies as originally proposed by Dean Tribble on this list [1] and then later expanded upon [2].
In a nutshell, their history is somewhat as follows: 1) original proxies could not emulate non-extensible objects or objects with non-configurable properties 2) direct proxies, by directly wrapping a specific target object, allow safe emulation of such objects/properties but at the expense of complex invariant checks. 3) notification proxies aim to get rid of invariant checks by only notifying the handler that an operation was performed on the proxy, and then automatically forwarding to the real target. The handler doesn't get to influence the result of an intercepted operation. Traps essentially become just notification callbacks (although the notification is synchronous). See the readme for details: https://github.com/tvcutsem/harmony-reflect/tree/master/notification There's also two examples: a generic logging proxy that just logs all intercepted operations, and a revocable reference, expressed as a notification proxy. For these two examples, notification proxies work out very well. They're even simpler than direct proxies because there's no need to manually forward. The notification proxy implementation (on top of old proxies) is also significantly simpler compared to direct proxies, so notification proxies are probably a lot simpler to specify as well. The remaining challenge with notification proxies is how to implement proxies where always forwarding all operations automatically does not make sense. Examples include membranes (need to wrap the result), and perhaps self-hosted exotics that aren't backed by any real "target". I haven't yet gotten around to implementing those. If anyone is willing to give it a try in the mean time, this would lead to valuable feedback. I realize we're close to the ES6 deadline and this would be a big change to proxies. At this time I'm not seriously proposing notification proxies as an alternative to direct proxies. We need more experience with them first. Cheers, Tom [1] https://mail.mozilla.org/pipermail/es-discuss/2012-November/026587.html [2] https://mail.mozilla.org/pipermail/es-discuss/2012-November/026589.html
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