@@new

[Erik Arvidsson]

On Wed, Jun 18, 2014 at 1:07 PM, Boris Zbarsky <bzbarsky at mit.edu> wrote:

> On 6/18/14, 11:39 AM, Erik Arvidsson wrote:
>
>> This also fits how @@create works for DOM, where the creation of the
>> instance would set up the internal DOM wrapper pointer, never exposing a
>> non initialized DOM object to user code.
>>
>
> Note that in that setup it's impossible to introduce an HTMLElement
> constructor like this:
>
>   var el = new HTMLElement("iframe");
>

This particular one can be done because if the constructor returns an
object that is used instead.

function HTMLElement(tagName = undefined) {
  if (tagName === undefined) throw ...
  var ctor = lookupConstructor(tagName);
  return new ctor;
}


> because the @@create doesn't have the tag name available to create the
> right sort of object...
>

But the constructor is able to return any object it want, basically making
the constructor into a factory method.

This is an ugly pattern so it is discouraged but it does give you some
leeway when you need to support strange things.

-- 
erik
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