My ECMAScript 7 wishlist

Dean Landolt dean at deanlandolt.com
Fri Sep 26 09:12:13 PDT 2014


On Fri, Sep 26, 2014 at 11:10 AM, Brendan Eich <brendan at mozilla.org> wrote:

> Dean Landolt wrote:
>
>> Out of curiosity, wouldn't Object.observe require implementors to add
>> precisely this kind of hook into the vm anyway?
>>
>
> No, but O.o has its own costs. See
>
> http://lists.w3.org/Archives/Public/public-script-coord/
> 2014JulSep/0204.html



Sure, O.o isn't free, and I get that using @noSuchProperty would likely
result in all kinds of deoptimization. But of all the costs listed in that
thread, I'm not seeing any mention of the cost of intercepting changes for
notification queueing. I'm assuming this has to be part of any O.o
implementation (IIUC the only alternative would be polling observed objects
every turn). More importantly that must already paid for all observed
objects. You made the comment "Good luck selling implementors", and I was
just wondering aloud whether they've already been sold on doing the heavy
lifting for the sake of O.o.

So to clarify: if this particular functionality is likely to be baked into
vms at some point in the future, ISTM this is a much stronger argument for
the kind of magic property Tab's advocating for. It could be supported
efficiently at the platform level, no Proxy baggage necessary. This
wouldn't be impossible in library code.
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