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  • Is it spec-compliant to forbid setPrototypeOf(Object.prototype, foo)?

Is it spec-compliant to forbid setPrototypeOf(Object.prototype, foo)?

# Michał Wadas (7 years ago)

Right now this code:

Object.setPrototypeOf(Object.prototype, Object.create(null))

throws in both Chrome and Firefox. I couldn't find any mention of special [[SetPrototypeOf]] of %ObjectPrototype%, did I miss something?

# T.J. Crowder (7 years ago)

On Thu, Feb 2, 2017 at 12:19 PM, Michał Wadas <michalwadas at gmail.com> wrote:

Right now this code:

Object.setPrototypeOf(Object.prototype, Object.create(null))

throws in both Chrome and Firefox. I couldn't find any mention of special [[SetPrototypeOf]] of %ObjectPrototype%, did I miss something?

Yes. :-) You missed that Object.prototype is an immutable prototype exotic object:

...which does indeed have a special [[SetPrototypeOf]] which (indirectly) returns false if you try to change the [[Prototype]]. Object.setPrototypeOf throws when [[SetPrototypeOf]] returns false: tc39.github.io/ecma262/#sec-object.setprototypeof

-- T.J.

# Michał Wadas (7 years ago)

Thanks, I erroneously looked at ES2015 spec that calls Object.prototype ordinary object.

The Object prototype object is the intrinsic object
%ObjectPrototype%. The Object prototype object is an ordinary object.
The value of the [[Prototype]] internal slot
<http://www.ecma-international.org/ecma-262/6.0/#sec-object-internal-methods-and-internal-slots>
of the Object prototype object is null and the initial value of the
[[Extensible]] internal slot
<http://www.ecma-international.org/ecma-262/6.0/#sec-object-internal-methods-and-internal-slots>
is true.
# T.J. Crowder (7 years ago)

On Thu, Feb 2, 2017 at 12:38 PM, Michał Wadas <michalwadas at gmail.com> wrote:

Thanks, I erroneously looked at ES2015 spec that calls Object.prototype ordinary object.

The Object prototype object is the intrinsic object %ObjectPrototype%. The Object prototype object is an ordinary object. The value of the [[Prototype]] internal slot www.ecma-international.org/ecma-262/6.0/#sec-object-internal-methods-and-internal-slots of the Object prototype object is null and the initial value of the [[Extensible]] internal slot www.ecma-international.org/ecma-262/6.0/#sec-object-internal-methods-and-internal-slots is true.

Ah! I looked in the ES2016 spec to make sure it wasn't a recent change, didn't think to go back to the one before...

-- T.J.

# Jordan Harband (7 years ago)

Also, Object.freeze causes Object.setPrototypeOf to fail.