Tom Van Cutsem <mailto:[email protected]>
September 13, 2013 6:36 PM
MarkM and I talked about conditional invocation offline and we
convinced ourselves to argue for the status-quo (i.e. continue to
encode conditional invocations as [[Get]]+[[Call]]).
The most compelling argument we can think of is that [[Get]]+[[Call]]
is also the pattern JavaScript programmers use to express conditional
method calls today:
var f = obj[name];
if (f) { f.call(…); } else { … }
No matter whether or how we extend the MOP, such code exists and will
continue to exist, and well-designed proxies that want to re-bind
|this| must already deal with this pattern by implementing the "get"
trap correctly.
Whew. Thanks.
We already have distinct "get" and "invoke" traps. Proxy writers must
already understand the dependency between these traps. Let's not make
things more complicated by adding a third, or by unnecessarily
complicating the signature of "invoke".
Or by adding boolean parameters if we can avoid 'em.
Given the status-quo, a proxy that wants to rebind |this| to the
target object must do so by overriding both "get" and "invoke". In the
"invoke" trap, |this|-rebinding is cheap (i.e. no need for bound
functions). In the "get" trap, it requires the handler to return a
bound function (which costs).
Right! JS has first-class functions, any memoizing vs. recreating is up
to the object, but some function must be found or created that binds the
right |this|.
But the cost will not be paid for ordinary method calls, which are
expected to be the common case.
Thanks again, to you and Mark.
/be
_______________________________________________
es-discuss mailing list
[email protected]
https://mail.mozilla.org/listinfo/es-discuss
