On Dec 4, 2009, at 1:52 PM, Mike Samuel wrote:
2009/12/4 Alex Russell <[email protected]>:
On Dec 4, 2009, at 9:38 AM, Mark S. Miller wrote:
On Fri, Dec 4, 2009 at 8:41 AM, Alex Russell
<[email protected]> wrote:
CommonJS modules don't solve the global pollution problem,
because they
can't. We're gonna keep blowing off limbs until we acknowledge
that there's
a design flaw in the language and take some positive action at a
semantic
level to correct it.
ES5 allows one to enumerate all properties on primordial objects
except the global (window) object, to attempt to delete all
properties
that are absent from a whitelist or die trying, and then to attempt
freeze all these cleaned up primordials (including all objects
reachable by traversal of remaining properties) or die trying. If
both
of these succeed...
...then you still can't keep someone from plunking something into
window.
for only their context. Not that you'd want to, but the language
still makes
you work harder than not to do the right thing. A missing "var"
still screws
the pooch.
Such a var would not pass the verifier.
ES5-strict enables to do a fully static scope analysis. Say one
builds
a static verifier for Program text that does nothing but reject text
that either 1) is not a valid ES5-strict program unit, 2) has free
variables, or 3) uses a direct eval operator. A "closed function"
is a
function that has no free variables. The natural rewrite of a module
is as the body of a closed function, perhaps packaged in a larger
closed expression or Program that would pass the above verifier.
Because ES5-strict is statically scoped, such a verifier effectively
removes the global object from the bottom of the scope chain of
Programs that pass this verifier.
Again, it's good that we can do it now, but the default policy hasn't
changed, you you'll forgive me if I'm somewhat skeptical that
opening the
door alone will bring in the thundering herds.
Rewriters can bridge the gap between correct verifier and
not-quite-correct code, by, e.g. introducing var declarations for free
variables.
Rephrased slightly for the entertainment of 3rd parties:
me: the problem is that people can still omit var
you: everyone will run it through a verifier
me: programmers are still human, particularly web developers. They
don't run verifiers. In general we still have the problem.0
you: everyone will run it through a verifier
me: really? And if they're going to accept the constraint anyway,
wouldn't it be better if we just created a construct where the default
is changed?
you: but everyone can just run it through a verifier!
me: um...
Lawls.
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