On Tue, Oct 25, 2011 at 12:59 PM, Scott Sauyet <scott.sau...@gmail.com>wrote:
> Lasse Reichstein wrote:
> > Bemi Faison wrote:
>
> > When you write "new MyClass()", you create and initialize an instance
> > of the abstract type. This is an object of a categorically different kind
> than
> > the constructor/prototype. When you start using that object as a
> prototype
> > of another constructor, you are mixing abstraction levels. That's why
> > people oppose doing "SubConstructor.prototype = new SuperConstructor".
>
> > The properties of a MyClass *instance* doesn't necessarily make sense
> > on the subclass, and they don't make sense when the same property is
> > inherited by all subclass instances.
>
> ... which is why if you do use a constructor in this fashion, you
> should always separate out the initialization into a separately-called
> function, one which is not called in this inheritance scenario.
>
No. The constructor does initialization logic. if you want an object to be
instantiated and initialized you either do
new constructor(...);
or
var o = Object.create(constructor.prototype);
o.constructor(...);
The latter splits instantiation and initiliazation. If you do not want the
object to be initialized then you simply don't use new and just instantiate
it using Object.create
>
> > When you write "Object.create(MyClass.prototype)", you just create an
> > object inheriting from the prototype. It's not initialized by the
> > MyClass constructor, it just inherits the methods of the abstract
> > MyClass type.
> >
> > Using that as the prototype of a new type keeps the abstraction level.
>
> I simply have never been quite certain when I can depend upon
> Object.create being present and functioning correctly. And I'm wary
> of shims which can never do what the original is supposed to do.
> Which is why I still mostly use:
>
> var F = function() {};
> F.prototype = Parent.prototype;
> Child.prototype = new F();
>
> This is perhaps less obvious than Object.create, but it's a well-known
> pattern, and I'm quite certain that the environments I care about
> support it., especially as my current project has to support IE7, and
> I would like it to support older versions of FF as well.
>
ES5 shim <https://github.com/kriskowal/es5-shim> will shim out a sensible
subset of ES5.
For example object.create(proto) works completely. Object.create(proto, pds)
works for some subset of pds.
Of course Object.defineProperty is iffy on support but we are not suggesting
you use. The only thing that really doesnt work at all in IE<9 is
getter/setters and enumerable/configurable/writable along with Object.freeze
and company.
however we are suggesting you use Object.create(proto) not
Object.create(proto, pd) the former works completely cross browser.
>
> I know there are many `Object.create` shims out there, but some of the
> properties that can be defined seem impossible to shim. Would there
> be any way to shim `ennumerable`?
>
> -- Scott
>
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