On 1/16/14 1:29 PM, Domenic Denicola wrote:
Hmm, I don't quite understand the concern.
You're creating new objects using things like Promise.cast(). That will
create an object whose prototype is Promise.prototype. But which
realm's Promise is it using in this case? That needs to be specified,
right?
What is special about promises that makes using them require specifying the
realm
Nothing.
whereas other web specs don't seem to need to? Or do other specs specify realms
too, and I just haven't noticed?
Here's what WebIDL says [1]:
Every platform object is associated with a global environment, just
as the initial objects are. It is the responsibility of
specifications using Web IDL to state which global environment
(or, by proxy, which global object) each platform object is
associated with.
so web specs do in fact need to do it. To the extent that they don't,
they're not actually defining the behavior and need to be fixed.
There's probably a lot of fixing to do, and I apologize on Mozilla's
behalf for not bringing up issues on this more proactively as we've been
converting objects to WebIDL bindings. :(
Similarly, ES6 builtin functions need to specify the realm for objects
they're creating. All the ones I've spot checked in fact do that, so
ES6 is way ahead of web specs here.
> An example underspecified scenario would be helpful, I think.
Here's an example not involving promises that's currently
underspecified, I believe:
window1.document.createElement.call(window2.document, "span");
I've put the relevant testcase at
http://web.mit.edu/bzbarsky/www/testcases/multiple-realms/createElement-1.html
if you want to take a look. Browsers consistently create the element in
the realm of window2 in this case, but the DOM spec doesn't seem to
actually define the behavior right now, unless I'm totally missing
something. It should do so, for example by defining that an element is
associated with the global environment of its owner document and then
defining the global environment for documents as needed. DOMParser and
XMLHttpRequest make that last bit slightly exciting.
Does that help illustrate the issue?
I do agree that this is a more wide-ranging problem than for promises,
by the way. At least in the createElement case we have compat across
UAs do right now; for other cases I'm not sure we necessarily do. :(
-Boris
[1] http://heycam.github.io/webidl/#es-platform-objects
