On May 11, 2011, at 11:51 AM, Mark S. Miller wrote:
>
>
> On Wed, May 11, 2011 at 11:41 AM, felix <[email protected]> wrote:
> I think he's proposing that the 'eval' function would be a magical
> function that can inspect its calling environment to determine whether
> it's being called in a lexically strict context or not, and based on
> that it would act like the strict eval operator, or not.
>
> That's exactly what I'm trying to determine. Such magical dynamic inspection
> of the caller's lexical context would be a form of dynamic scoping. Nowhere
> else in the language can a callee detect a caller's strictness.
This is the key point that I haven't seen otherwise mentioned on this thread.
Classically JS eval as implemented by browsers required knowledge about its
calling environment that generally isn't passed by a normal function call. To
make this work, either this extra information has to be passed in every call to
any function (any call might be to an aliased eval call) or there has to be a
dynamic scoping mechanism that allows eval to reach up the stack and get out of
band information from it caller. Neither of these were things we wanted to
require of implementations in ES5.
"Direct eval" (or the eval operator, as Oliver refers to it) is a way to
(mostly) statically identify eval calls and to do special case processing to
make the caller environment information available for eval processing.
"indirect evals" are just regular function calls and not special environment
information is passed or otherwise made available. So, the built-in eval
function when indirectly involved is limited to using the global environment.
This has nothing to do with strict mode.
Allen
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