jQuery 3.0 Released

Consider the relatively common use-case - there is a service object which proxies requests, format's the call to the backend (or fetches from cache) and format's the returned response for the caller of the object. So the pattern looks something like: ServiceObject.fetchData(query).then((data) => { / * display data * / }, (err)=> { / * catch error - display no results * /})

At some-point you want to chain the promise to update another part of the ui: promise.then((data) => { /* display something else / }, (err) => { / catch error - display failed to load */ }).

The problem is you can't squash the error in the 'reject' of the previous promise now, because otherwise the error isn't propagated to the last promise in the link and instead you will hit the 'success' function. This 'reject' behavior is alright if there is something your 'success' function can do when the original request failed, but in a great majority of cases if the request failed there is nothing you can do - you put a 'reject' in the first chain of the promise resolution (potentially in the serviceObject itself) with some generic flash-message like 'request failed please try again' and call it good. As it stands you end up with a call chain where what a function higher up in the chain should return should be based on what a resolving function further down the chain is doing -- not having to do this was for me was almost entirely the plus-side of the promise-style over callbacks-style concurrency model.

I bring this up now because curiously the jQuery model of Deferred() precisely did not do this before -(see section#2 of Major Changes):

> Example: returns from rejection callbacks

if an error wasn't re-thrown in a catch, the promise-handling would stay in the 'reject' chain as long as an error had been thrown. I am quite curious as to why the current-model won, I understand some of the potential benefits but in practice I find that this behavior is worse in 90% of use-cases that I have encountered. If someone has a link to a mailing-thread / issue where this was discussed I would be quite interested.

something like $("#wrapperel").on("click",".painbutton",cbfunction),is way more code in plain js.