Bug 48953 – REGRESSION: Can't shadow/overwrite window.constructor (causes TypeError exception)

• Status: RESOLVED
• Resolution: FIXED
• Component: JavaScriptCore

[Matt Cooper]

In the latest WebKit nightly, I am seeing an unexpected error message:

TypeError: Result of expression 'TestSample' [[object DOMWindowConstructor]] is not a constructor.

for code that works just fine in Apple Safari 5.0.2, Google Chrome 7.0.517.41, and Firefox 3.6.11.

----

var constructor = new Function("id", "desc", "this.id = id; this.description = desc;");
constructor.prototype.setDescription = function(desc){this.description = desc};
constructor.prototype.getDescription = function(){return this.description};

// Changing the order of the following 2 lines does not make a difference:
window["TestSample"] = constructor;
constructor.getInstanceFromFactory = function (id, desc){return new TestSample(id, desc);};

var sample = TestSample.getInstanceFromFactory("hello","success if you see this");
alert(sample.getDescription());

----

Expected result is that you see an alert with the text "success if you see this" but in WebKit nightly, the above JavaScript TypeError is logged in the JavaScript console instead.

[Matt Cooper]

Created attachment 72868 [details]
This attachment is simply an html test page that houses the code that throws the unexpected TypeError in WebKit nightly only

[Matt Cooper]

This issue is still reproducing over a month later in r74228 (today's latest nightly).

I also see the problem manifest on pages like this one:
http://jdevadf.oracle.com/adf-richclient-demo/faces/index.jspx

[Alexey Proskuryakov]

<rdar://problem/8790587>

[Geoffrey Garen]

The bug here is that window.constructor (a property that exists on all objects by default) can't be shadowed / overwritten.

[Geoffrey Garen]

I believe this may have been caused by Michael's recent change to the DOMWindow constructor object.

[Michael Saboff]

It appears that this was caused with change set <http://trac.webkit.org/changeset/69553>, the change to https://bugs.webkit.org/show_bug.cgi?id=47422  "DOMWindow constructor directly callable".

[Michael Saboff]

Created attachment 77274 [details]
Patch to allow setting window.constructor.

Added a new extended attribute to the JavaScript code generator called ReplaceableConstructor that will generate a setJS<class>Constructor() method.  Added this attribute to the DOMWindow interface.
Updated a test and added a new regression test.

[Michael Saboff]

Created attachment 77277 [details]
Updated patch with whitespace fixes.

[Michael Saboff]

Committed revision http://trac.webkit.org/changeset/74537

[Matt Cooper]

Note that while this bug was fixed in WebKit, the issue still manifests in the mobile version of Safari on iOS 4.3.