Rxjs use of instanceof breaks subscription with multiple bundles

[Avocher]

Bug Report

Current Behavior
Hi, we are building a components that exposes rxjs observables for plugins to connect to. Our component is primarely used prebundled, which means that our plugin creators might have double of some parts of rxjs. Though, somewhat wastefull this worked fine with rxjs 5, but after upgrading to rxjs 6, things started breaking in Firefox and Chrome Canary 69. Here's the error message they get when trying to subscribe:

TypeError: You provided an invalid object where a stream was expected. You can provide an Observable, Promise, Array, or Iterable.

Which pointed at the subscribeTo function, where I suspect that this line is the culprit:

rxjs/src/internal/util/subscribeTo.ts

Line 15 in 80ceea0

if (result instanceof Observable) {

instanceof seems to be a bit unreliable and appears to work differently under the hood in each browser, especially if the class appears twice and originated from the same source.

Reproduction

1. Create two bundles referencing rxjs 6.2.0, one exposing an observable, another subscribing to it and using its own operators.
2. Try to subscribe.

Expected behavior
Should subscribe since there is nothing (?) stopping it from doing so.

Environment

• Chrome 69 & Firefox 60
• RxJS version: 6.2.0

If anyone knows a workaround I'd be happy with that, since I know some would probably regard this as a non-issue.

[benlesh]

It sounds like you're bundling two instances of RxJS. That's not going to be good for your app size. Your libraries shoudl have RxJS as a peer dependency, and that will solve the problem most likely.

However, there are workarounds:

1. Load a polyfill for Symbol.observable. RxJS 5 used to polyfill it for you. RxJS 6 doesn't, because libraries shouldn't be doing that. If Symbol.observable is present, then each copy of RxJS will coerce to it's own Observable type using that.

2. Use a from call to wrap observables you think come from other libraries.

... but the real solution here is that you'd want RxJS to be a peer dependency.

[benlesh]

We might start using our isObservable implementation internally, and that could solve this issue, but it's also sort of a smell in the usage here. We'll discuss it at the next core team meeting.

[Avocher]

Thank you for the help Ben! Yes, our current setup isn't ideal. Your suggestions will have to serve as a band aid for the time being until we get our distribution setup sorted out.

[benlesh]

After some discussion with the team today, we've decided to leave the instanceof checks as is. Because:

1. There are performance implications of moving away from instanceof checks
2. The work around is as easy as polyfilling Symbol.observable.