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

Matthew Robb matthewwrobb at
Tue Nov 3 14:41:10 UTC 2015

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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