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

Justin Novosad junov at google.com
Wed Jul 17 16:21:53 PDT 2013

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 the concern is more about code
readability.  Is that it?

> I guess I'm asking for JS dev input here...
> Promises are just regular callbacks, with the synchronisation done by the
> browser (or shim library) rather than by author code. I don't really
> understand the problem here.

Yes. In the case of createImageBitmap the resolver would be built-in to the
promise by the browser, so there is nothing to set-up. Devs who are not
ready to fully embrace Promises can use this API the same way they would a
callback API, but with a slightly different syntax:

Not too scary IMHO

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

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