Symbols, Protocols, Frames, and Versioning

Kevin Smith khs4473 at
Fri Oct 5 08:07:28 PDT 2012

>  - Symbols, even when not used for encapsulated abstractions, are
> great for avoiding the possibility of collision in the global string
> namespace
>  - So, we (tc39) decided to use them for to replace the property name
> currently called "iterator" in Spidermonkey.
>  - Currently, "iterator" works across same-origin frames, but a naive
> use of Symbol for this wouldn't work
>  - Therefore, we have a few options:
>    1 Give up on Symbols for "iterator"
>    2 Make the Symbol replacement for "iterator" magically work across
> all same-origin frames
>    3 Make iteration not work across frames
>    4 Break the web and fix cross-frames to work more sensibly
>  - Since the latter two of those are not actual options, (2) seemed
> like the best choice.
>  - But then we, the language, are doing something that programmers
> can't do, so we searched for something else
>  - This led to `Symbol.for`, which is not actually allowing
> programmers to do (2), but resembles it somewhat

Good breakdown, but note that the problem isn't strictly confined to
cross-frame situations.  See last paragraph of the original post about
protocol versioning.

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