Oliver Hunt pointed out the bug in SpiderMonkey's implementation (in Firefox 3.5) of Object.getPrototypeOf, where a primitive value does not cause a TypeError to be thrown as specified in ES5 draft. This bug was based on some miscommunication [1] and it will be fixed ASAP [2].
Throwing on non-Object (Object the spec type, not only instances of the Object native constructor) is as specified for all of the new Object metaprogramming APIs. But throwing differs from the behavior on primitives of the three ES3 Object.prototype additions, hasOwnProperty, getPrototypeOf, and propertyIsEnumerable, which convert |this| using the ToObject spec-internal helper function.
I bring this up not to lobby for a change to ES5 as drafted, just to note the inconsistency. This came up at a TC39 meeting a while ago and my notes say the committee was willing to use ToObject for getPrototypeOf, but the change was not made. Again, probably for the best.
It would be great in Harmony to remove more of the Java-inspired primitive type "specialness", compatibly if possible but in stricter strict mode if necessary. I'm not sure how to do it in a way that helps getPrototypeOf, but even without a specific proposal, it helps to note that it's easier to relax an error condition in the future than to try to impose one.
So again, no ES5 change needed, just discussion fodder.
/be
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