2011/8/30 Brendan Eich <[email protected]> > On Aug 30, 2011, at 2:16 PM, David Bruant wrote: > > Actually that's what current function proxies do by default (no .prototype > unless otherwise specified). My suggestion is to put a .prototype by default > with keeping the option to opt-out (same with .length, etc.) > > Right, of course function proxies have to trap in order to emulate > .prototype and other properties. >
Indeed, that was our intent: fproxy.prototype and fproxy.length are determined by the handler via the "get" trap. This should work fine for fproxy.prototype (and it is actually consulted when evaluating |obj instanceof fproxy|.) For fproxy.length, the handler object can only return the call trap's length if it has a reference to the call trap, which as David points out, in the general case it does not. OTOH, typically a function proxy will wrap some other target function f, in which case the handler would simply return f.length, so I don't know whether this issue is such a big deal. If one wraps an existing function f using the default ForwardingHandler like so: var fproxy = Proxy.createFunction(new ForwardingHandler(f), f); Then fproxy.prototype, .length, .arguments, and .caller will all work as expected. So the default ForwardingHandler is in a sense already the convenient library that Andreas alluded to. I do notice that .prototype and .length are non-configurable properties, so that ups the ante for proxies being able to emulate non-configurable properties (more about that later). Cheers, Tom
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