ES4 draft: enumerability

Jason Orendorff jason.orendorff at
Tue Apr 22 14:06:58 PDT 2008

On 2008/4/10, Lars Hansen <lhansen at> wrote:
> Here's the first draft explaining how enumeration works in ES4.

* It's unclear which parts of this, if any, are intended to be

* Are the terms "enumeration", "iteration", and "itemization" defined
  somewhere?  Even if they are, I can't stop reading the first two as
  synonyms, so I'd welcome a change in terminology.  Perhaps "for-in
  iteration" for "enumeration", and "for-each-in iteration" for

* The treatment of for-each-in (the last sentence) is a bit vague.  The
  only difference is how the iterator "IT" is obtained, right?  But that
  needs to be specified.

  Renaming "GET" and "DEFAULT_GET" to something like
  "FOR_ITERATOR" and "DEFAULT_FOR_ITERATOR" would leave room for

* The iterator proposal specifies additional special behavior when the
  iterator "IT" is a generator-iterator.  Intentionally omitted here?

* Is a more general introspection facility planned?  If so, I hope
  DEFAULT_GET can be defined in terms of that and the Enumerator class
  can be dropped.

* The design of Enumerator doesn't make sense to me, especially that
  it's a parameterized class.  What's the design goal here?

  To expose "get obj's public, enumerable properties, just like ES3
  for-in", a static method suffices:

    Object.getEnumerableProperties(obj: Object!): Iterable.<string>

  If the goal is to expose a general API for getting various slices of
  an object's set of property names, a static method still suffices:
        obj: Object!,
        deep: boolean = true,
        withDontEnum: boolean = false,
        namespaces: (boolean|Iterable.<Namespace>) = false)
     : Iterable.<Name>

  Either way, DEFAULT_GET is easily defined in terms of that.


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