If you want to create a clean-slate proxy object -- for example, a dictionary
-- then you can't predefine toString or valueOf. But this means your object
will always fail at the semantic operations [[ToString]] and [[ToPrimitive]].
For example:
> var obj = Proxy.create(myEmptyHandler, proto);
> String(obj)
TypeError: can't convert obj to string
> obj + ""
TypeError: can't convert obj to primitive type
If you actually instrument the proxy to watch which operations it's trying,
you'll see:
> var obj = Proxy.create(myEmptyHandler, proto);
> String(obj)
trying: toString
trying: valueOf
TypeError: can't convert obj to string
> obj + ""
trying: valueOf
trying: toString
TypeError: can't convert obj to primitive type
Should we not offer derived traps for toString and valueOf (which, if not
defined, default to looking up the "toString" and "valueOf" properties,
respectively, on the receiver), to allow for stratified implementation of this
reflective behavior, i.e., without polluting the object's properties?
Dave
PS SpiderMonkey also has the unstratified Object.prototype.toSource, which is
used for the non-standard uneval function, for printing out values at the
console. This is kind of unfortunate since it suggests a need for another proxy
trap, but this time it's not for a standard functionality.
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