It could be a version number, the modified date, or a hash of the content - which is what I do on this blog.
Most server-side frameworks come with tools to make this easy (I use Django's ), and there are smaller libraries that achieve the same thing, such as gulp-rev.
For a web site, it is a major component in achieving high performance.
On the other side, it has to be configured properly as not all resources stay identical forever: it is important to cache a resource only until it changes, not longer.
Getting caching right yields huge performance benefits, saves bandwidth, and reduces server costs, but many sites half-arse their caching, creating race conditions resulting in interdependent resources getting out of sync.
The vast majority of best-practice caching falls into one of two patterns: Each URL contains something that changes along with its content.
A fresh representation is available instantly from a cache while a validated representation rarely sends the entire representation again if it hasn’t changed. an ETag/Last-modified header), and a lack of explicit freshness info, it will usually (but not always) be considered uncacheable.The performance of web sites and applications can be significantly improved by reusing previously fetched resources.Web caches reduce latency and network traffic and thus lessen the time needed to display a representation of a resource.Seriously, given the basic spelling and grammar mistakes I make, I need to be able to update content quickly and frequently.isn't possible, the server always sends the full content.