On 21 August 2013 16:02, Erik Arvidsson <[email protected]> wrote:
> Here is a proof of concept using Proxy (Spidermonkey only)
>
> http://jsbin.com/AWIs/2/edit
>
> It rewrites the `with (expr)` with `with (createUnscopeable(expr))`
> where createUnscopeable returns a proxy that filters out the black
> listed property names.
A small nitpick: that implementation doesn't quite work, because it
does not delegate other operations correctly. The wrapping proxy will
leak into the object as receiver. Consider:
var o = {
__unscopeable__: ['a'],
a: 1,
f: function() { return 'a' in this }
}
with (createUnscopeable(o)) {
f() // false!
}
A proper implementation would require explicit delegation for all
receiver-aware traps. Left as an exercise. :)
/Andreas
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