Bug 47672 – ES5 strict mode bugs

• Component: JavaScriptCore
• Status: RESOLVED FIXED

[kangax]

There are 3 oversights in the way strict mode works in webkit, which results in 4 failing tests with the above example page — http://kangax.github.com/es5-compat-table/strict-mode/

Also, for the ref, early error on "assignment to an unresolved reference" was discussed here — https://mail.mozilla.org/pipermail/es5-discuss/2010-October/003742.html

[Alexey Proskuryakov]

The tests being:

__i_dont_exist = 1; is a ReferenceError
arguments++; is a SyntaxError
(function(){ return this === undefined; })();
(function(){ return this === undefined; }).call();

[Oliver Hunt]

Fixing the reference error for global properties at the moment

[Oliver Hunt]

__i_dont_exist = blah should now be fixed.

[Oliver Hunt]

pre-/post-fix operations on arguments are now disallowed.

[Oliver Hunt]

i've got the null vs. undefined |this| fix up for review now

[Oliver Hunt]

And now the undefined vs null patch is landed.

kangax are there any other problems you've found?

[kangax]

Hey Oliver.

I don't have this fresh build yet, but the previous one seems to also fail to set strict mode for eval code (in certain cases). For example:

(function(){ "use strict"; eval('with({ }) { }') })(); // no error

To quote 10.1.1:

"Eval code is strict eval code if it begins with a Directive Prologue that contains a Use Strict Directive or if the call to eval is a direct call (see 15.1.2.1.1) to the eval function that is contained in strict mode code."

Note "direct call [...] contained in strict mode code". So based on my understanding (and actually, FF4 behavior) this should throw error, but currently doesn't.

[Oliver Hunt]

(In reply to comment #7)
> Hey Oliver.
> 
> I don't have this fresh build yet, but the previous one seems to also fail to set strict mode for eval code (in certain cases). For example:
> 
> (function(){ "use strict"; eval('with({ }) { }') })(); // no error

Was this in the inspector? I'm seeing weird behaviour where code in the inspectors console fails to trigger strict mode

[kangax]

(In reply to comment #8)
> (In reply to comment #7)
> > Hey Oliver.
> > 
> > I don't have this fresh build yet, but the previous one seems to also fail to set strict mode for eval code (in certain cases). For example:
> > 
> > (function(){ "use strict"; eval('with({ }) { }') })(); // no error
> 
> Was this in the inspector? I'm seeing weird behaviour where code in the inspectors console fails to trigger strict mode

Ah. yes it was. Doesn't happen when run from within <script> element. 

Well, then I have nothing else as far as strict mode. Will file bugs if I find anything.

[Oliver Hunt]

(In reply to comment #9)
> (In reply to comment #8)
> > (In reply to comment #7)
> > > Hey Oliver.
> > > 
> > > I don't have this fresh build yet, but the previous one seems to also fail to set strict mode for eval code (in certain cases). For example:
> > > 
> > > (function(){ "use strict"; eval('with({ }) { }') })(); // no error
> > 
> > Was this in the inspector? I'm seeing weird behaviour where code in the inspectors console fails to trigger strict mode
> 
> Ah. yes it was. Doesn't happen when run from within <script> element. 
> 
> Well, then I have nothing else as far as strict mode. Will file bugs if I find anything.

I just landed a fix for the Function constructor which should appear in the next nightly

[kangax]

I think I'm seeing browser crash under strict mode. Filed a separate bug for it — https://bugs.webkit.org/show_bug.cgi?id=48109

Oliver, can you please take a look?

[Gavin Barraclough]

All the strict mode tests pass for me in ToT.