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fix(service-worker): check for updates on navigation

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Currently the Service Worker checks for updates only on SW startup,
an event which happens frequently but also nondeterministically. This
makes it hard for developers to observe the update process or reason
about how updates will be delivered to users. This problem is
exacerbated by the DevTools behavior of keeping the SW alive
indefinitely while opened, effectively preventing the page from
updating at all.

This change causes the SW to additionally check for updates on
navigation requests (app page reloads). This creates deterministic
update behavior, and is much easier for developers to reason about.
It does leave the old update-on-SW-startup behavior in place, as
removing that would be a breaking change.

Fixes #20877
This commit is contained in:
Alex Rickabaugh
2017-12-14 13:10:06 -08:00
parent 0b2d636b75
commit 20e1cc049f
3 changed files with 55 additions and 8 deletions
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14
aio/content/guide/service-worker-devops.md
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@ -32,12 +32,10 @@ server can ensure that the Angular app always has a consistent set of files.
#### Update checks
Every time the Angular service worker starts, it checks for updates to the
app by looking for updates to the `ngsw.json` manifest.
Note that the service worker starts periodically throughout the usage of
the app because the web browser terminates the service worker if the page
is idle beyond a given timeout.
Every time the user opens or refreshes the application, the Angular service worker
checks for updates to the app by looking for updates to the `ngsw.json` manifest. If
an update is found, it is downloaded and cached automatically, and will be served
the next time the application is loaded.
### Resource integrity
@ -276,8 +274,8 @@ with service workers. Such tools can be powerful when used properly,
but there are a few things to keep in mind.
* When using developer tools, the service worker is kept running
in the background and never restarts. For the Angular service
worker, this means that update checks to the app will generally not happen.
in the background and never restarts. This can cause behavior with Dev
Tools open to differ from behavior a user might experience.
* If you look in the Cache Storage viewer, the cache is frequently
out of date. Right click the Cache Storage title and refresh the caches.