Patched __proto__ (that uses Object.setPrototypeOf) fails and throws TypeError

[lauritzthamsen]

There seems to be an issue with how proto is patched to use Object.setPrototypeOf.
Currently, setting the proto property of an object causes a TypeError:

TypeError: Generic use of proto accessor not allowed

The error occurs, for example, when using test/testProxies.html to run testProxies.js in the testSetPrototypeOf.

Is there another way to patch proto?

I used Chrome 29.0.1547.22 beta (with Experimental JavaScript for the old Harmony proxies and Harmony Weak Maps).

My current solution is to prevent the patch (not executing the function after _var _proto__setter), change Object.setPrototypeOf to directly set the proto property, and then consistently use

Object.setPrototypeOf(target, newProto)

instead of

target.proto = newProto

in the project... :-/

[tvcutsem]

This seems to be an issue with Chrome itself rather than my patch: Chrome advertises Object.prototype.proto as an accessor property with a setter, but actually calling the setter produces an error:

var protoDesc = Object.getOwnPropertyDescriptor(Object.prototype,'__proto__');
protoDesc.set.call({}, {}); // TypeError: Generic use of __proto__ accessor not allowed

I updated reflect.js so that Object.setPrototypeOf throws a 'not supported on this platform' exception on Chrome, as I have no way of implementing it without being able to call the setter. In the new patch, I also leave Object.prototype.__proto__ alone in this case, such that normal uses of object.__proto__ = v should still work.

Update to reflect.js v0.0.7 to see the patch.

I also filed a bug with v8, asking for clarification:
https://code.google.com/p/v8/issues/detail?id=2804

Thanks for reporting.

[lauritzthamsen]

Wow. Thanks for looking into this, the clarification, and the workaround. And for filing the issue with v8.

[lauritzthamsen]

This seems fixed. The status of the issue you filed with v8 was set to fixed and worked for me in the most recent Chrome.

Thanks for your help again!

[tvcutsem]

No problem!