Bug 170549 – Cannot Object.seal() or Object.freeze() global "this"

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[Michael Saboff]

The ECMAScript standard describes a isExtensible method for Proxy objects that forwards on to the wrapped object.  See <https://tc39.github.io/ecma262/#sec-proxy-object-internal-methods-and-internal-slots-isextensible>. We don’t have that method in JavaScriptCore.

<rdar://problem/31478302>

[Saam Barati]

(In reply to Michael Saboff from comment #0)
> The ECMAScript standard describes a isExtensible method for Proxy objects
> that forwards on to the wrapped object.  See
> <https://tc39.github.io/ecma262/#sec-proxy-object-internal-methods-and-
> internal-slots-isextensible>. We don’t have that method in JavaScriptCore.
> 
> <rdar://problem/31478302>

The spec you linked to is for ProxyObject, not JSProxy. Perhaps the JSProxy info is in the HTML spec?

[Michael Saboff]

(In reply to Saam Barati from comment #1)
> (In reply to Michael Saboff from comment #0)
> > The ECMAScript standard describes a isExtensible method for Proxy objects
> > that forwards on to the wrapped object.  See
> > <https://tc39.github.io/ecma262/#sec-proxy-object-internal-methods-and-
> > internal-slots-isextensible>. We don’t have that method in JavaScriptCore.
> > 
> > <rdar://problem/31478302>
> 
> The spec you linked to is for ProxyObject, not JSProxy. Perhaps the JSProxy
> info is in the HTML spec?

I should have been more specific.  This is needed for the global "this" as it is a JSProxy to the global object.  JSProxy doesn't implement isExtensible, but ProxyObject does.

[Michael Saboff]

Changing the bug title to the symptom of the problem instead the cause.  Doing this since it appears the fix requires changes to other code besides JSProxy.

[Michael Saboff]

Created attachment 306423 [details]
Patch

[Michael Saboff]

Comment on attachment 306423 [details]
Patch

View in context: https://bugs.webkit.org/attachment.cgi?id=306423&action=review

> Source/JavaScriptCore/interpreter/Interpreter.cpp:1162
> +                    return checkedReturn(throwTypeError(callFrame, throwScope, ASCIILiteral(ReadonlyPropertyWriteError)));

A better error message is NonExtensibleObjectPropertyDefineError.  I made that change locally.

[Mark Lam]

Comment on attachment 306423 [details]
Patch

r=me

[Michael Saboff]

Fix landed in change set r215072: <http://trac.webkit.org/changeset/215072>