Hi Mark, Tom!
I understand that you are currently working on finalizing a number of
aspects of the proxies proposal, so I thought I'd send my current
notes on issues I discovered. (Sorry if I'm a bit late with that, but
I just returned from travelling.)
Here is a list of minor issues. I'll send a separate mail describing
what I think is a more fundamental problem with the current spec.
- Proxy.create: What if the handler passed is not an object? Should we
throw right away?
- Proxy.create: What if the prototype passed is neither an object nor
null? FF silently sets it to null in all other cases, but that seems
inconsistent with Object.create, which throws.
- Proxy.createFunction: More of a question, but do we really want to
support a separate construct trap for function proxies? I would argue
that it was a mistake to ever make a distinction between a regular and
a construct call. Even if we cannot clean that up, we should perhaps
avoid having it proliferate further, in the proxy interface.
- Derived get/set traps: They use .call on accessor functions taken
from a user-defined descriptor. Such a function might itself be a
proxy, in which case .call is not necessarily defined. Should invoke
it through Function.prototype.call.call instead. (There may be other
places in the current ES spec that assume that all functions have a
call method. I think they should all be changed.)
- Also, we should specify that the JS code assumes that all used
intrinisc properties are the original methods.
- Object.{seal,freeze,preventExtensions}: When sealing a function
proxy, how do we initialize the standard properties length,
constructor, prototype, caller, and arguments? What if the proxy does
not define them already, or returns unsuitable values?
- Function.prototype.toString: should this work for function proxies?
- Function.prototype.bind: requires additional language explaining how
the length property is set if the curried function is a proxy.
- JSON: don't we need some changes here, too? For example, step 6a of
the JO operation (15.12.3) talks about the "names of all the own
properties" of an object. Clearly, for a proxy we need to invoke the
appropriate trap here.
- Outside the (current?) standard, but pragmatically, how should we
treat .__proto__ on a proxy? FF and V8 both treat it as an ordinary
property for proxies, but that implies that Object.getPrototypeOf(p)
!= p.__proto__ in general.
- ToStringArray, step 6.a: s/array/O/
/Andreas
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