Commits on Feb 21, 2024

1. DOM: Reorder Observable completion events …

   This CL "fixes" Observable unsubscription/teardown timing. As a matter
   of accidental historical precedent, Observables in JavaScript (but not
   in other languages) had implemented the "rule" that upon
   Subscriber#error() or Subscriber#complete(), the subscriber would:
    1. First, invoke the appropriate Observer callback, if provided (i.e.,
       complete() or error() callback).
    2. Signal abort Subscriber#signal, which invokes any teardowns and also
       fires the `abort` event at the signal.
   
   However, after dom@chromium.org discussed this more with
   ben@benlesh.com, we came to the conclusion that the principle of "as
   soon as you know you will teardown, you MUST close the subscription and
   any upstream subscriptions" should be adhered. This means the above
   steps must be inverted. This is a small-in-size but medium-in-impact
   design change for the Observable concept, and led to a blog post [1] and
   an announcement [2] that the RxJS library intends to change its
   historical ordering of these events.
   
   This CL:
    1. Inverts the order of the aforementioned steps in the Blink
       implementation.
    2. Improves some tests that assert this new ordering.
    3. Simplifies the takeUntil() operator in general.
   
   The Observable spec will be updated alongside this commit:
   WICG/observable#120.
   
   [1]: https://benlesh.com/posts/observables-are-broken-and-so-is-javascript/
   [2]: ReactiveX/rxjs#7443
   
   R=masonf@chromium.org
   
   Bug: 1485981
   Change-Id: I376e66eef490808d264dc999862a801d591aa278
   Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/5311097
   Commit-Queue: Dominic Farolino <dom@chromium.org>
   Reviewed-by: Mason Freed <masonf@chromium.org>
   Cr-Commit-Position: refs/heads/main@{#1263562}

   

   domfarolino authored and chromium-wpt-export-bot committed Feb 21, 2024
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