Default `this` value for static promise functions

Brendan Eich brendan at mozilla.org
Tue Apr 7 17:46:53 UTC 2015


a.d.bergi at web.de wrote:
> Hi,
> I've just got bitten by
>
>      return getError().then(Promise.reject);
>
> where `reject` threw an error that its `this` value was not a Promise constructor.
>
> Would it help to make the `C` constructor (in Promise.resolve, Promise.reject, Promise.all, Promise.race algorithms) default to `Promise` when no `this` value is supplied (throw only if it's there, but not an object and constructor function)?

No, because as you suggested:

> Or is this considered to be too error-prone with Promise subclassing, where `.then(MyCustomPromise.reject)` would not work as expected (fail silently)?

Probably the best solution is an arrow:

     return getError().then(r =>  Promise.reject(r));


/be


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