direct_proxies "problem"

Brendan Eich brendan at
Sat Jan 12 09:53:26 PST 2013

Allen Wirfs-Brock wrote:
>> All good except it's impossible/not meant to recognize Proxies in JS 
>> world?
> Note that Tom said: "recognize /their/ proxies" (emphasis added).  If 
> it needs to, a membrane or any other proxy issuing subsystem should be 
> able to recognize its own proxies.  It can, for example, tag them 
> using a private symbol or keep them in a weak map.  You don't want to 
> recognize other subsystems proxies as proxies.  They're just objects 
> to you.

Critical point -- same as if we ignore proxies and have two separate 
systems whose objects must satisfy certain constraints that are internal 
to each system. Yes, APIs for these systems should be more structurally 
typed, IMHO -- but sometimes you need high integrity and performance. In 
such cases, what amounts to nominal types or brands come into play. 
There may be no universal domain of discourse for objects in a given 

Wishing the DOM were entirely self-hosted and "open-box" is just not 
realistic. As Boris points out, CSS selector matching must not trigger 
traps or getters, and must be parallelizable.


More information about the es-discuss mailing list