BTW, there's still usefulness of making resolution/rejection idempotent and never throwing. IMHO, I'd just like to see this die.
----- Isiah Meadows [email protected] On Tue, Feb 28, 2017 at 4:36 PM, Jordan Harband <[email protected]> wrote: > Although now that I think about it, it wouldn't have to care about the > promise state, `resolve` and `reject` could just throw if they're invoked > more than once. > > On Tue, Feb 28, 2017 at 1:35 PM, Jordan Harband <[email protected]> wrote: > >> That seems like it would allow synchronous observation of Promise state - >> consider: >> >> ```js >> >> function isResolved(promise) { >> try { >> new Promise((resolve) => { >> resolve(promise); >> resolve(); >> }); >> } catch (e) { >> return true; >> } >> return false; >> } >> >> ``` >> >> On Tue, Feb 28, 2017 at 12:58 PM, Isiah Meadows <[email protected]> >> wrote: >> >>> Also, making promise resolution idempotent makes dealing with things way >>> easier. Similarly, most deferred libraries ensure their resolution is >>> idempotent. >>> >>> On Tue, Feb 28, 2017, 13:20 Tab Atkins Jr. <[email protected]> wrote: >>> >>>> On Tue, Feb 28, 2017 at 10:12 AM, /#!/JoePea <[email protected]> wrote: >>>> > f.e. >>>> > >>>> > ```js >>>> > let resolve >>>> > let p = new Promise(r => resolve = r) >>>> > >>>> > resolve(5) // resolves the promise. >>>> > resolve(4) // noop (in Chrome), but why not throw an error? >>>> > ``` >>>> > >>>> > I only tested in Chrome, and I'm assuming it follows spec, but I >>>> could be >>>> > wrong. >>>> > >>>> > I'm asking because it seems that throwing an error will prevent shots >>>> in the >>>> > foot, so that code doesn't assume that resolving on an already >>>> resolved >>>> > Promise worked, although it didn't. It seems like it can lead to >>>> unexpected >>>> > failures. >>>> >>>> That's correct behavior, yes. In general, it's because the internal >>>> state of a promise is meant to be unobservable unless you're >>>> specifically listening to it. >>>> >>>> ~TJ >>>> _______________________________________________ >>>> es-discuss mailing list >>>> [email protected] >>>> https://mail.mozilla.org/listinfo/es-discuss >>>> >>> >>> _______________________________________________ >>> es-discuss mailing list >>> [email protected] >>> https://mail.mozilla.org/listinfo/es-discuss >>> >>> >> >
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