fromFetch throws AbortError when resubscribed

[aquark]

Bug Report

Current Behavior
When an Observable created with fromFetch is unsubscribed and then resubscribed, it immediately throws AbortError.

Reproduction

const o$ = fromFetch(url, {})
o$.subscribe()
o$.unsubscribe()
o$.subscribe()

Expected behavior
Each subscription to the observable should be independent. Looking at the code, the problem is that the init object from the function parameters is reassigned within the observable. Since this variable is from the closure it is shared across subscriptions, so subsequent subscriptions use the same abort signal which was already aborted and therefore always abort immediately.

Environment

• Runtime: Node 12
• RxJS version: 6.5.4

Possible Solution
Instead of reassigning to the function parameters, assign to a local variable within the Observable.

As a workaround, always wrapping the fromFetch in defer should work.

[cartant]

It's possible that this was fixed in master - in #5110 - but not backported to version 6.

[cartant]

Yeah. You are right. It needs to assigned to a variable that's declared within new Observable. It should not be assigned to the parameter.