The subject of Web resource caching is as old as the World Wide Web itself. However, I'd like to offer an as-exhaustive-as-possible catalogue of how one can improve performance by caching. Web resource caching can happen in two different places: client-side - on the browser and server-side. This post is dedicated to the former; the next post will focus on the latter.
Caching 101
The idea behind caching is simple: if a resource is time- or resource-consuming to compute, do it once and store the result. When somebody requests the resource afterwards, return the stored result instead of computing it a second time. It looks simple - and it is, but the devil is in the detail, as they say.