Andrew Scott
e16dab82a1
This commit removes special (undocumented) logic in the Router code that is
meant to prevent duplicate navigations that result from location syncs in
AngularJS/Angular hybrid applications.
The duplicate navigations can occur when both the Router and the AngularJS sync
code detect a location change via a popstate/hashchange event. When this
happens, the Angular Router schedules a navigation to sync itself with
the browser, but the hybrid listener may also schedule an additional
navigation. There are a few reasons this logic should not be included in
the Router:
* This special logic is not tree shakeable so it introduces a bundle
size cost for all applications, most of which don't need it.
* There have been many updates to the routing pipeline to tolerate
duplicate navigations. That is, duplicate navigations can happen and
routing should still complete successfully.
* https://github.com/angular/angular/commit/0e8548f667e5fdefa3ac7cdf1ba47e3e17011ffc
* https://github.com/angular/angular/commit/9e039ca68bfae5328f3fc1f16fabd7673c466a25
* The logic is really in the wrong place: The hybrid sync code should be
the location to handle this. If duplicate navigations are meant to be
avoided, the hybrid sync code should have handling to _not_ trigger
duplicate navs.
* This logic _also_ used to exist because the mock location
helper used for test incorrectly triggered popstate events during
router navigations. In order to avoid unexpected behavior in tests, this
logic needed to be added. This incorrect mocking may also have been
put in place because the upgrade module _would_ see a location change
event and trigger a duplicate navigation. The location mock has since been updated to
match real browser behavior so this is no longer necessary. The
upgrade module has also been updated to not trigger duplicate
navigations. The following commits are related to this:
* https://github.com/angular/angular/commit/202a1a56314af4ddb99c476f974536a10e390319
* https://github.com/angular/angular/commit/c6a93001eb74374b0fbc6aea1286fe1183d21382
Side note: The `setTimeout` in the location change listener is used to
ensure the ordering of duplicate navigations was consistent. You can see
that the logic being removed here expects the imperative navigation to precede the
popstate/hashchange. With the removal of this code, the `setTimeout` no
longer serves a purpose. However, it has been found that tests can rely
on this behavior (incorrectly) because they expect the navigation to be
complete but in reality, it hasn't even started because the test has not
flushed the timeout. Removing the timeout would be a breaking change as
a result.
PR Close #45240
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