v2: Backbone.Promise

[jridgewell]

DO NOT MERGE, BREAKING CHANGE This is for the next major, v2.

Competes with #2489.

Specifically, it implements Backbone.Promise instead of Backbone.Deferred, so it can be easily swapped with any ES6 compatible Promise library.

This is phase 1. Phase 2 would be:

• returning a Backbone.Promise from Backbone.sync.
• removing all the options.success and options.error callbacks in favor of chained promises.
  • That includes transitioning from success callbacks to rejected promises, ie. Model#fetch where validation fails with the server's attributes.

[tgriesser]

For any "major breaking change" PR's such as this #3649, #3644 or others where existing tests are being significantly altered/added it might be wise to create / PR against a 2.0 branch so it doesn't put master in a state where patch releases can't be made against the current master 1.x master.

Thoughts? /cc @braddunbar @jashkenas @akre54

[megawac]

Agreed with @tgriesser (as long as the branches remain rebasable), and :+1: to adding BB.Promise

[braddunbar]

That sounds good to me. :+1:

[Cleod9]

Referencing this ticket: https://github.com/jashkenas/backbone/issues/3739

I just wanted to bring the above to everyone's attention since if Promises are implemented some extra care should probably be taken to make sure that certain error() arguments I mentioned are not lost somewhere in the promise. Otherwise I could anticipate some scary situations where devs are confused on the reason of an ajax failure when no relevant detail is provided by the Promise's error handler.

[jeromecovington]

Allowing developers to handle their own polyfills is desirable in general and more forward-thinking, provided the specific polyfills that meet BB's requirements are clearly documented as such.

[jeromecovington]

+1 @Cleod9 re: error handling. Inadvertently handling errors with a .catch() without re-throwing up the Promise chain can be a huge source of debugging confusion.

[godlark]

I think if we want to return a promise it would be good to pass parsed response to then's callback. Read more at https://github.com/jashkenas/backbone/pull/3779

[marlun]

Have there been any further development on this?

[mjeanroy]

Hi, it seems that Backbone plans to use promise as the return value of the sync method in a futur major release and it's a good news :+1:

However, what about XHR abortion ? Currently, according to the official spec, it's not possible to cancel a promise, but aborting an ajax request is an important feature I guess. How will you handle this case ?

[akre54]

We can either wrap the promise for you, and attach an abort method, or you can do that yourself in Backbone.ajax. I'm inclined towards the latter, unless there's enough of a reason to add it to core.