On Wed, Apr 27, 2011 at 2:46 PM, David Bruant <[email protected]> wrote: > You're right. "get" and "set" default traps were chosen to follow > closely internal methods (see [1]) and at the time when "proxy" wasn't > an argument of all traps (so a proxy's prototype wasn't reachable from > the handler). > It may be a good idea to rethink default trap implementations by > imposing the recursivity and start from there to rewrite internal methods. > I think that pretty much all proto-climbing traps could be rewritten as: > --- > trap: function(/*arguments*/, proxy){ > var res = Object.ownLayerTrap(proxy); > return satisfying(res)? > res: > Object.trap(Object.getPrototypeOf(proxy)); > } > --- > The only exception I can think of is "set" which may me slightly more > complicated.
When listing property names (i.e. "getPropertyNames", "enumerate", "iterate") it is actually a concatenation of both own and prototype values, not just one vs. the other. Also with "getPropertyDescriptor", there needs to be logic to return |undefined| when the prototype is null. > Actually, the leak already exists. If y has a "p" property which is an > accessor, then when performing x.p, the |this| binding of "get" and > "set" accessors is x (not y). ES5 8.12.3 [[Get]]: > The descriptor /desc/ has been found *somewhere* in the prototype chain, > /getter/ is extracted from it and O is bound as the |this| value (step 13) > Same deal with [[Put]]. > So, proxies do not leak more than ES5 getters/setters do. > Actually, the only place where "receiver" is used in the default get and > set trap is as an argument for desc.get.call or desc.set.call. Excellent point, the leak occurs either way. However, the leak does occur *differently* (i.e. via a "receiver" argument instead of a |this| binding), which does not have to be the case. As explained before, the existing ES5 semantics would cause the proxy's "getPropertyDescriptor" trap to be called thus obtaining any "getter" / "setter" that the proxy wants. The |this| binding of this "getter" / "setter" will then be set to the "receiver" by ES5 8.12.3 step 13 for a "getter" or ES5 section 8.12.5 step 5.b for a "setter". The proxy's "get" / "set" trap would not get called, and thus would not need the "receiver" arguments. Thanks, Sean Eagan _______________________________________________ es-discuss mailing list [email protected] https://mail.mozilla.org/listinfo/es-discuss
