On Nov 9, 2009, at 6:50 PM, Garrett Smith wrote:
[[Construct]] of Function.prototype is not standardized.
The definition of Function.prototype does not define the expected
behavior for [[Call]] or [[Construct]]. Instead, there is a
description of what happens when it is invoked:
| 15.3.4 Properties of the Function Prototype Object
| The Function prototype object is itself a Function
| object (its [[Class]] is "Function") that, when
| invoked, accepts any arguments and returns undefined.
Should Function.prototype implement [[Construct]]? Either way, the
specification should state the outcome.
Yes, it's a slightly tricky one :) I was wading through Sputniktests
suite couple of days ago (when finishing web runner — http://thinkweb2.com/projects/prototype/sputniktests-web-runner/
) and noticed that there were assertions for exactly this kind of
compliance.
I even filed a bug with Sputniktests, thinking that they make
incorrect assumptions — http://code.google.com/p/sputniktests/issues/detail?id=11
However, then I realized that specs do in fact mention this
explicitly, although not directly under these specific sections.
If you look into Section 15 — Native ECMAScript Objects, you'll see
this rather clear explanation:
"[...] None of the built-in functions described in this section shall
implement the internal [[Construct]] method unless otherwise specified
in the description of a particular function. None of the built-in
functions described in this section shall initially have a prototype
property unless otherwise specified in the description of a particular
function. [...]"
In fact, I mentioned this exact phrase when writing about bugs in
various browsers, revealed through Sputniktests web runner (http://thinkweb2.com/projects/prototype/sputniktests-web-runner/#construct-and-prototype-of-builtins
).
And as I said in a post, Firefox and Chrome, for example, fail a whole
bunch of tests due to most of built-in methods (like
`Array.prototype.toString`, `parseInt` or `String.prototype.slice`)
implementing [[Construct]] and having .prototype properties.
[...]
--
kangax
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