Save Object.observe()! (please) + make WeakMap/WeakSet observable.

Matthew Robb matthewwrobb at
Tue Nov 3 20:43:04 UTC 2015

Isiah, could you elaborate some? I can't quite tell if you are expressing
support for my suggestion or not. Thanks!
On Nov 3, 2015 12:13 PM, "Isiah Meadows" <isiahmeadows at> wrote:

> Lol... I feel I'm in an insane minority that can work relatively
> productively in Java 7 and Haskell both.
> Of course, I have a preference, but that preference lies around that of
> OCaml and Clojure. It's more the expression-based, impure functional
> languages that I'm most productive in. Observing mutations that I react to
> using immutable data structures. Sounds very odd and/or blasphemous to
> some, but that's what I like. MVC models like that are how Mithril and
> similar smaller frameworks have started to get some attention. It prefers
> highly local state, and an observed object would be a great state model for
> that.
> And on that note, I'm going to stop before I derail the topic too far.
> On Tue, Nov 3, 2015, 11:26 Andrea Giammarchi <andrea.giammarchi at>
> wrote:
>> That would make functional-programming-oriented developers wining forever
>> about such monstrosity in  specs ... I'd personally love such possibility!
>> Regards
>> On Tue, Nov 3, 2015 at 2:41 PM, Matthew Robb <matthewwrobb at>
>> wrote:
>>> I probably have a terrible understanding of how this all works at a low
>>> level but I feel like a potential solution would be a method of "upgrading"
>>> a non-proxy object to be a proxy. The reason accessors are being used as
>>> they are now is because you can retro fit them. Maybe what I am suggesting
>>> is essentially like swapping out the internal pointer of an object with
>>> another object (such as the way live module bindings work). In this way you
>>> might upgrade an existing object to behave like a proxy.
>>> - Matthew Robb
>>> On Tue, Nov 3, 2015 at 3:20 AM, Tom Van Cutsem < at>
>>> wrote:
>>>> 2015-11-02 23:34 GMT+01:00 Coroutines <coroutines at>:
>>>>> I come from Lua.  In Lua we make proxy objects with metamethods.  You
>>>>> create an empty table/object and define a metatable with a __index and
>>>>> __newindex to catch accesses and changes when a key/property doesn't
>>>>> exist.  I would primarily use this in sandboxes where I wanted to
>>>>> track the exact series of operations a user was performing to modify
>>>>> their environment (the one I'd stuck them in).
>>>> For this type of use case, you can use an ES6 Proxy <
>>>> You can think of the proxy handler's methods as the 'metamethods' of the
>>>> proxy object.
>>>> What O.o would provide beyond Proxy is the ability to observe changes
>>>> to already pre-existing objects. However, since you mention you'd start
>>>> with an empty table/object, you should be able to create a fresh Proxy and
>>>> use that to trace all property accesses.
>>>> Proxies are particularly well-suited when you want to sandbox things,
>>>> since you should be in control of the sandboxed environment anyway and can
>>>> set-up proxies to intermediate. O.o is particularly well-suited to
>>>> scenarios where there are already plenty of pre-existing objects and you
>>>> don't know ahead of time which ones to observe and which not.
>>>> Cheers,
>>>> Tom
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