Intent to Ship: Iterable Array-like interfaces ("IterableCollections")

[Caitlin Potter]

Contact emails

caitpo...@gmail.com

Spec

http://heycam.github.io/webidl/#es-iterators

Summary

This is a small WebIDL bindings feature, which adds a property named Symbol.iterator, with value %ArrayProto_values%[1], to any WebIDL interface with an integer-typed "length" attribute, and an indexed property getter.

This was originally implemented back in October, 2015, in https://codereview.chromium.org/1381413003, behind the RuntimeEnabledFlag "IterableCollections".

Removing this flag exposes the Symbol.iterator on the following interfaces:

CSSRuleList, CSSStyleDeclaration, ClientRectList, DOMStringList, DataTransferItemList, FileList, HTMLAllCollection, HTMLCollection, HTMLFormElement, HTMLOptionsCollection, HTMLSelectElement, MediaList, MimeTypeArray, NamedNodeMap, Plugin, PluginArray, SVGLengthList, SVGNumberList, SVGPointList, SVGStringList, SVGTransformList, SourceBufferList, Storage, StyleSheetList, TextTrackCueList, TextTrackList, TouchList, webkitSpeechGrammarList

In addition, it also exposes Symbol.iterator, and methods "forEach", "values", "keys", and "entries", on NodeList. These methods behave

similarly to how they do on ECMAScript Array objects.

Is this feature supported on all six Blink platforms (Windows, Mac, Linux, Chrome OS, Android, and Android WebView)?

Yes

Interoperability and Compatibility Risk

This change is largely compatible with the implementation in Firefox 48 --- One exception is that Symbol.iterator is currently installed on Window, but a spec change has since made this invalid. The property being inserted on Window is in the process of being removed (and would be removed automatically if the indexed property getter were removed from Window, as it has been removed in the spec[2].

OWP launch tracking bug

This is currently being tracked at crbug.com/538558[3].

Entry on the feature dashboard

There currently is none, as this is a very small feature, and very low cost, and is primarily implemented to enable a simple convention introduced in ECMAScript 6, rather than to enable some new exciting feature.

[1] https://tc39.github.io/ecma262/#sec-array.prototype.values

[2] https://github.com/whatwg/html/commit/acae3df652b382e9f4f1d1b4dc7e08e2b00df821

[3] https://crbug.com/538558

[Boris Zbarsky]

On 3/14/16 12:50 PM, Caitlin Potter wrote:
> Interoperability and Compatibility Risk
>
> This change is largely compatible with the implementation in Firefox 48

One minor note: Firefox does not implement forEach/values/keys/entries
on NodeList at the moment. Not sure whether anyone does, so there might
be some compat worries around that.

For the rest, this is awesome news. :)

-Boris

[Jochen Eisinger]

Do you plan to remove the iterator symbol from Window before shipping?

[Caitlin Potter]

Yes, there's a CL for removing iterator from Window open, and should land before or soon after a shipping CL lands

[Jochen Eisinger]

lgtm1

[Rick Byers]

LGTM2

[Chris Harrelson]

LGTM3

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