When executing this code:
(function () {
eval(var x=delete(x))
})()
I think the assertion in the ECMAScript description of the declarative
environment record's SetMutableBinding algorithm, 10.2.1.1.3 step 2, fails.
* On entry to the function, we create a lexical environment
This is a bug in the spec, and has been previously discussed here:
https://mail.mozilla.org/pipermail/es5-discuss/2010-November/003839.html
(Thanks, Jeff!)
On 03/20/2011 11:22 PM, Jim Blandy wrote:
When executing this code:
(function () {
eval(var x=delete(x))
})()
I think
On 08/25/2010 12:30 PM, Allen Wirfs-Brock wrote:
(this should probably have been posted to es5-discuss rather than es-discuss)
Most of the work in 15.4.5.1 step 3 is about maintaining array length
invariants that are outside the scope of the default [[DefineOwnProperty]]
specification.
Given that 15.4.5.2 makes arrays' length properties non-configurable, it
seems to me that all the care taken in step three of the custom
[[DefineOwnProperty]] method in 15.4.5.1 is to no avail, as the default
[[DefineOwnProperty]] will refuse to make any changes anyway.
I've filed a Trac
On 10/14/2009 06:36 PM, Mike Shaver wrote:
Our implementation of String.prototype.match checks the context in
which it's called, to see if it need bother with the expense of
constructing the result array (it needn't, if the match call is being
used simply as a test, which isn't unheard of on
On 10/15/2009 07:23 AM, Maciej Stachowiak wrote:
The latter, if truly allowed by the spec, makes source-to-source
transformers, even something as simple as a pretty-printer,
potentially unsound. That seems like a much less bounded form of
insanity.
I think this point is well-taken.
In
On 10/15/2009 09:29 AM, Jason Orendorff wrote:
I sort of doubt that everyone who touches the
compiler is even aware of the constraint.
/me tries to look inconspicuous
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On 10/15/2009 02:18 PM, Allen Wirfs-Brock wrote:
Maciej's thought experiment touches upon the fundamental evil of host objects.
In the presence of host objects there is no firm foundation for understanding
the semantics of an ECMAScript program. Adding some additional restrictions on
host
On 10/13/2009 04:05 PM, Mike Shaver wrote:
On Tue, Oct 13, 2009 at 7:01 PM, David-Sarah Hopwood
david-sa...@jacaranda.org wrote:
I agree with Maciej. The implementation-defined operations have clear
specifications of their parameters. I think that it is highly undesirable
to adopt an
One could characterize the difference by saying that Mozilla has
reluctant properties whereas WebKit has reluctant values. :)
In other words, in WebKit, 'document.all' has a value --- a value that
can be assigned to other variables, stored in data structures, and so on
without changing its
Object.defineProperty lets one change the Writeable attribute with:
Object.defineProperty(obj, prop, ({writeable:state}))
The way that's currently defined, we just convert that one-property
object to a property descriptor and pass it to [[DefineOwnProperty]].
It's a nice way to change a
On 06/01/2009 01:31 PM, Jeff Walden wrote:
Note the footnote: I was referring to the spec type, not to an object
describing a property descriptor provided by JS code. That omitted
properties on such objects (even extension properties) be treated as
if they were set to their default values
Section 11.1.1, The this keyword, refers to the ThisBind field of
the execution context; it should be ThisBinding.
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Like the 'with' statement, the 'catch' clause of a 'try' statement can
establish local bindings. In both cases, the spec describes this in
terms of changing the execution context's LexicalEnvironment temporarily
and then restoring it.
In the description of 'with', there is a NOTE assuring
In section 10.2.2.2, algorithm step 2 refers to the declarative
environment record type by the StUdLyCaPs name
DeclarativeEnvironmentRecord, which is never defined or used elsewhere.
Perhaps it should simply be declarative environment record, as used
elsewhere in the section.
The last sentence of the first paragraph should end with ... the result
depends on the value of the S argument:.
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In Appendix C, The Strict Mode of ECMAScript, the paragraph noting
that VariableDeclaration and VariableDeclarationIn may not assign to
eval in strict mode doesn't cite any particular section number;
shouldn't it cite 12.2.1?
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The definitions of the SetMutableBinding method for both declarative and
object environment records (10.2.1.1.3 and 10.2.1.2.2) refer to
SetMutableValue in their first sentence. This name doesn't occur
anywhere else; I assume they're supposed to be SetMutableBinding.
The second paragraph of 4.2.2 says:
A complete ECMAScript program may be composed for both strict mode and
non-strict mode ECMAScript code units.
Shouldn't that say ... may be composed of both ...?
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