On 8/23/13 1:23 PM, Tab Atkins Jr. wrote:
On Fri, Aug 23, 2013 at 10:22 AM, Anne van Kesteren <[email protected]> wrote:
On Fri, Aug 23, 2013 at 6:09 PM, Boris Zbarsky <[email protected]> wrote:
If we want to continue returning void when a callback is passed, we need to
add some webidl magic for that...
My idea was to always return a promise. And if a callback is passed
you just pass that to the promise "as listener".
Yeah, we can just auto-add the callback as a .then() argument on the
returned promise. Maybe then return the promise returned by .then(),
rather than the original?
Given the last definition of then() I saw, this has a bit of a gotcha.
Consider this code:
function callback() {
throw "Hey"
}
someAPI(callback);
now in today's world, when some API calls back into callback an
exception is reported to the console and window.error and whatnot.
But if someAPI internally does:
var promise = new Promise();
return promise.then(callback);
then all throwing from callback will do is set up the error state on the
return value; the exception is not reported anywhere.
Now UAs might end up reporting to the console when a promise with an
unhandled error is GCed or something. But window.onerror is SOL in this
case.
-Boris
