On 4/10/12 4:23 PM, Tab Atkins Jr. wrote:
On Tue, Apr 10, 2012 at 1:16 PM, Boris Zbarsky<[email protected]> wrote:
On 4/10/12 4:13 PM, Tab Atkins Jr. wrote:
According to current WebIDL spec, an object with a named property
getter exposes the list of names as own properties, so you can get
them with for-in enumeration.
1) for-in enumeration enumerates prototype properties.
Yes, but prototype properties aren't own properties, so you can tell them apart.
Yes, but it's a huge pain that no one will actually remember to do.
I didn't say there is _no_ way to enumerate the objects. I said there
is no _good_ way. There's a difference. If you expect people to
commonly need to enumerate the set of named flows, then there is
something to be said for making it easy and safe, not hard and footgunny.
2) for-in enumeration enumerates expandos which might have nothing to
do with the set of named properties.
It's not possible to set an expando on a map object like this. (The
setter operation will either do something useful, or will reject the
attempt to set.)
The setter for interfaces that support named properties is not applied
to things outside the set of supported property names per current WebIDL
[1]. So if the set of supported property names here is the set of flow
names, then expandos with other names can be defined. The proposal on
this list didn't actually say what the set of supported property names
is, but the proposal at
http://lists.w3.org/Archives/Public/www-style/2012Feb/0327.html does say
that the supported property names are the flow names.
-Boris
[1] Specifically,
http://dev.w3.org/2006/webapi/WebIDL/#defineownproperty step 3 is where
we would end up. If the name is not a supported property name,
'creating' is set true in step 3.1. We enter step 3.2, because we do
not have a property named P. Since 'creating' is true, we skip step
3.2.1. Since 'creating' is false and there is no named property
creator, we skip step 3.2.2. So we end up in step 4, which just does a
completely normal JS property set on the object; now we have an
"expando" property.
