Better Caching With stale-while-revalidate Directive in Cache-Control Header
HTTP Headers Update
The stale-while-revalidate directive can be used alongside max-age inside Cache-Control response header to further strengthen caching policies.
<!-- cache is fresh for 120 seconds, but still can be used for 60 seconds more -->
Cache-Control: max-age=120, stale-while-revalidate=60
Historically cached responses older than max-age are considered stale. The browser then proceeds to get fresh data, and then that data is used to render content to the user.
But with stale-while-revalidate, the expired cached data may still be used for some more time, while browser asynchronously fetches a fresh copy. This makes it possible to render content using the expired cached data right away, while ensuring fresh data for the next time.
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