Inconsistency between RSVP.Promise and native promises

[boris-petrov]

After reading the last posts in here:

https://discuss.emberjs.com/t/readers-questions-why-does-ember-still-use-rsvp/14736

I tried removing all mentions of RSVP.Promise in our code base. We are using the latest Ember.js (3.4.4) and the latest Ember-CLI (3.4.3). I have at least one case where there is still some difference between the two. I've put up a reproduction repo:

https://github.com/boris-petrov/ember-promise-bug

Running ember test causes one failure. If you uncomment import { Promise } from 'rsvp'; in the test, it passes. Which means that using a native promise is different than using an RSVP one. By reading the reader's question, I was under the impression that since Ember 3.4 they should be interchangeable.

Also, you can see that resolve('text!'); is commented out - if you uncomment it (and comment out the line above it which resolves the promise in a later) the test passes using both Promise types. Not sure why and how all this is connected...

Any insight would be appreciated!

[ef4]

Thanks for taking the time to reproduce.

This code is racy. The test does not await the asynchronous behavior in the helper. I made a PR to your reproduction that shows how to make the test reliable.

I need to clarify what I said about native Promises: they absolutely work fine in Ember, and the helper in your example behaves correctly when implemented with a native Promise. But they don’t have identical timing, so if you are relying on races or side effects, you can observe different behavior. So the caveat is: you can switch from RSVP.Promise to Promise as long as you are waiting for the promise to resolve.

[boris-petrov]

@ef4 - thank you very much for the explanation! That definitely resolved our issue we had. I should have thought about the fact that the test doesn't wait for native promises but it does for RSVP ones.

A question while we're at it - I'm currently trying to rewrite a bunch of our CoffeeScript to TypeScript and I noticed that some classes/interfaces are defined as taking/extending RSVP.Promise instead of just Promise/PromiseLike - most notably PromiseProxyMixin. This breaks my TypeScript code and I have to suppress the warnings. So:

1. It is fine using PromiseProxyMixins with native Promises I think?
2. Are you going to change the type definitions now that RSVP is not "required" and as I read it will eventually be even removed as jQuery?

[ef4]

I'm not sure what the plan is for PromiseProxyMixin. It should work fine with native promises, but its public API proxies a method (finally) that isn't on native Promise, so I don't know how to make typescript happy about that. Seems worth opening a separate issue to discuss.

[chriskrycho]

I've added a comment over on the ember-cli-typescript issue linked above in this thread clarifying why our types are what they are and what some possible workarounds may be.