Promise.cast and Promise.resolve

Kevin Smith zenparsing at gmail.com
Tue Jan 28 22:14:10 PST 2014


>
>
>  This seems like something that can be deferred to ES7.
>>
>
> Which "this"? .chain is deferred to ES7, and in V8 experimentally.


Deferring `chain` is, if not future-hostile to `chain`, then
"future-irritant".

The way Promises are currently spec'd, the return value of the `then`
callback is itself recursively unwrapped using `then`, rather than the more
appropriate single-unwrapping of `chain`.  Single unwrapping of the output
side is consistent with the AP2 design principal that the provider does not
determine the unwrapping policy.

You cannot consistently implement AP2 without `chain` from the get-go.  It
is the primitive unwrapping function which `then` should be calling.
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