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docs(service-worker): add staleWhileRevalidate strategy (#37301) 

There is great workaround for implementing staleWhileRevalidate strategy in service-worker by setting strategy to freshness and timeout to 0u. Documented this in service worker config where all other strategies are documented

Fixes #20402

PR Close #37301
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Ajit Singh 2020-06-06 08:44:12 +05:30 committed by atscott
parent 779344012a
commit db11a0ddbf
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aio/content/guide/service-worker-config.md
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@ -193,6 +193,21 @@ The Angular service worker can use either of two caching strategies for data res
* `freshness` optimizes for currency of data, preferentially fetching requested data from the network. Only if the network times out, according to `timeout`, does the request fall back to the cache. This is useful for resources that change frequently; for example, account balances. * `freshness` optimizes for currency of data, preferentially fetching requested data from the network. Only if the network times out, according to `timeout`, does the request fall back to the cache. This is useful for resources that change frequently; for example, account balances.
<div class="alert is-helpful">
You can also emulate a third strategy, [staleWhileRevalidate](https://developers.google.com/web/fundamentals/instant-and-offline/offline-cookbook/#stale-while-revalidate), which returns cached data (if available), but also fetches fresh data from the network in the background for next time.
To use this strategy set `strategy` to `freshness` and `timeout` to `0u` in `cacheConfig`.
This will essentially do the following:
1. Try to fetch from the network first.
2. If the network request does not complete after 0ms (i.e. immediately), fall back to the cache (ignoring cache age).
3. Once the network request completes, update the cache for future requests.
4. If the resource does not exist in the cache, wait for the network request anyway.
</div>
### `cacheQueryOptions` ### `cacheQueryOptions`
See [assetGroups](#assetgroups) for details. See [assetGroups](#assetgroups) for details.