Bug 131698 – Simple ES6 feature: Array.from

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Oliver Hunt]

http://people.mozilla.org/~jorendorff/es6-draft.html#sec-22.1.2.1

Should be doable in builtin JS

[Radar WebKit Bug Importer]

<rdar://problem/16625961>

[Antoine Quint]

Dupe of 130966, landed in http://trac.webkit.org/changeset/167797.

*** This bug has been marked as a duplicate of bug 130966 ***

[Antoine Quint]

Wrong bug, sorry!

[Caitlin Potter (:caitp)]

This bug should be simple, but is at least partially blocked on iterators being available.

[Oliver Hunt]

We support for-of on all currently iterable types, as well as the spread operator so should be either

Return [...arguments]

Or 

Return [...source]

I can't recall spec of the top of my head

[Caitlin Potter (:caitp)]

You're correct, for-of and the spread operator are supported for certain types (although strings appear to not be iterable yet in JSC).

However, iterator methods seem to be attached via private properties / internal slots, rather than using the well-known symbol @@iterator.

The Array.from algorithm uses `GetMethod(items, @@iterator)` to determine whether or not it can use the from-iterable path or the from-array-like path, so an implementation is still sort of blocked on that (or at least blocked on exposing a getter for the private iterator properties to JS builtins, if it is to be implemented in JS).

[Oliver Hunt]

I would actually say that the hardest part here will be updating the builtins generation logic to support constructor/static functions.

The subsequent logic would be to expose (as a private global) the Symbol object, with @@iterator attached. (You'd still need to use for-of.  Our internal iterator implementation doesn't match spec behaviour for reasons best summed up as "performance")

[Oliver Hunt]

note builtin JS can do magical things - look at the js files in builtins/

[Geoffrey Garen]

This is done.

[Geoffrey Garen]

http://trac.webkit.org/changeset/183357