>>> It's a mistake to mix up the two-level distinction in JS, though.
>>> Backward compatibility and the ==/=== invariant require typeof to
>>> classify a certain way that cannot capture instanceof. You can't fold
>>> the two into one.
Internally, probably not, because primitives are fundamentally different. But
what the user is seeing is different. I’ve used JavaScript for years, without
knowing about the difference. And one often reads “everything is an object in
JavaScript” on the web, because the illusion is really quite well maintained
(*except* for typeof vs. instanceof).
But “a better instanceof” is something that can be prototyped as a library
function. I’ll do so and will also try to figure out what the actual use cases
for typeof/instanceof are – this kind of categorization is indeed a bit of an
anti-pattern (I think Allen pointed that out recently).
>> As I read it (and as I see it), there was not a call for folding the two
>> into one. I see it as a call to "institutionalize" the de-facto status quo,
>> where typeof distinguishes between objects ("object" and "function") and
>> primitives/atoms (everything else), while primitives/atoms are
>> 2nd-level-distinguished among themselves by the actual typeof value (objects
>> do not, they use instanceof or other means to do it).
That would be nice as a complementary measure. Especially "null" would be
great, but it seems like a risky change. Having both "object" and "function" is
something that’s unfortunate, but unfixable.
> Axel wrote
>
> "At the moment, things are a mess (between typeof, instanceof,
> [[Class]], Array.isArray, cross-frame communication, etc.). And I
> wouldn’t want that mess to get even worse."
>
> and he is right, but the complaints there come from instanceof failing
> cross-frame.
Right, sorry for conflating two issues. My main point was: any kind of
simplification of the current situation helps (even typeof o === "null" which,
OTOH, might not be worth the risk).
Regarding cross-frame: Many explanations on the web of determining whether a
value is an array sound like this is an impossible task (ignoring
Array.isArray()) and that’s a shame. Alas, I’m not sure how one could do better
here, it’s really a tricky problem. postMessage seems like a partial solution.
> Just to repeat, and I'm not sure where Axel stands on this: extending typeof
> does not make this problem worse. But I do not see a way to extend typeof to
> solve the cross-frame object classification problem.
I agree. typeof should (at most) be slightly updated to keep up with changes
and to become less quirky.
Axel
--
Dr. Axel Rauschmayer
[email protected]
home: rauschma.de
twitter: twitter.com/rauschma
blog: 2ality.com
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