HTTP Header

https://developer.mozilla.org/zh-CN/docs/Web/HTTP/Headers

Cache Header

HTTP Cache Headers - A Complete Guide - KeyCDNKeyCDN

https://devcenter.heroku.com/articles/increasing-application-performance-with-http-cache-headers

Caches work with content mainly through freshness and validation. A fresh representation is available instantly from a cache while a validated representation rarely sends the entire representation again if it hasn't changed. In cases where there is no validator present (e.g. ETag or Last-Modified header), and a lack of explicit freshness info, it will usually (but not always) be considered uncacheable. Let's shift our focus to the kind of headers you should be concerned about.

Extension Cache-Control directives#

Apart from the well-known Cache-Control directives outlined in the first section of this article, there also exists other directives which can be used as extensions to Cache-Control resulting in a better user experience for your visitors.

Cache-Control: max-age=<seconds>
Cache-Control: max-stale[=<seconds>]
Cache-Control: min-fresh=<seconds>
Cache-control: no-cache 
Cache-control: no-store
Cache-control: no-transform
Cache-control: only-if-cached

immutable#

No conditional revalidation will be triggered even if the user explicitly refreshes a page. The immutable directive tells the client that the response body will not change over time, therefore, there is no need to check for updates as long as it is unexpired.

stale-while-revalidate#

The stale-while-revalidate directive allows for a stale asset to be served while it is revalidated in the background.