Non-generic traps for non-generic objects (was: Overriding Map/etc with get/set hooks?)

Sam Tobin-Hochstadt samth at
Fri May 24 15:22:12 PDT 2013

On Fri, May 24, 2013 at 5:52 PM, Tab Atkins Jr. <jackalmage at> wrote:
> On Fri, May 24, 2013 at 2:35 PM, Ron Buckton <rbuckton at> wrote:
>> Another way to look at this is that there is no way to prevent a caller from using methods from the superclass on a subclass. In other OO languages, its much harder (or nearly impossible depending on the language) to forcibly call a superclass method against a subclass that has been overridden by the subclass.
>> Tab wouldn't have this issue if there were a way to prevent an external caller from executing if the mapSubclass overrides `set`.
> Sure, but that's attacking it on the wrong level, I think.
> The problem is that the Map#set method grabs an *internal property*,
> bypassing Proxies, etc., so you can't defend against it.  If I could
> intercept access to [[MapData]] via proxy traps (like David suggests
> in the OP), everything would be *perfect* - every single problem I
> have would be resolved successfully, as would every additional
> possibility that Jason brings up.

Are you suggesting that the authors of JS abstractions should never
use private state because then subclasses couldn't modify the behavior
of that internal state?


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