[whatwg] Proposal: createImageBitmap should return a "Promise" instead of using a callback

Ian Hickson ian at hixie.ch
Wed Jul 17 17:00:08 PDT 2013

On Wed, 17 Jul 2013, Justin Novosad wrote:
> On Wed, Jul 17, 2013 at 6:54 PM, Ian Hickson <ian at hixie.ch> wrote:
> > On Thu, 18 Jul 2013, Silvia Pfeiffer wrote:
> > > At the same time, I think we should follow a clear pattern for 
> > > introducing a Promise based API, which the .create() approach would 
> > > provide.
> >
> > I don't understand what that means.
> I think the concern is about the case where we end up with legacy 
> callback Factory methods that co-exist new with Promise-based flavors of 
> the factory methods. There's no technical obstacle to having the two 
> co-exist with the same name, it's just an overload.

I guess I don't understand what methods we're talking about here. Can we 
be more concrete? I am very much in favour of not having redundant APIs, 
not having lots of different kinds of APIs. But I'm not aware of this 
problem existing here. We have constructors and synchronous factory 
methods, have had for over a decade, and we're slowly adding constructors 
where it makes sense and not adding new synchronous factory methods. But 
in the case of ImageData, we need an asynchronous factory. This is unusual 
in the Web; mostly we have instead returned incomplete objects. In this 
case, the whole point of the API is to avoid this. This means we need a 
callback mechanism; Promises are a good, non-invasive way to do this.

Ian Hickson               U+1047E                )\._.,--....,'``.    fL
http://ln.hixie.ch/       U+263A                /,   _.. \   _\  ;`._ ,.
Things that are impossible just take longer.   `._.-(,_..'--(,_..'`-.;.'

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