Question

What are the complete set of factors that affect image caching in web browsers? How much control does a web developer have over this, and how much is browser settings? Are there different considerations for other types of assets (i.e. scripts, audio)?

Thanks

Answer 1

The complete set of factors:

• HTTP headers which affect caching
• the user agent’s (browser’s) built-in caching behavior
  • may be modified through user settings, depending on UA
  • including private browsing modes that may use and then clear a separate cache per session
• the user’s actions, such as manually clearing the cache

Web developers have very little control, but this is fine. Remember that caching is done for the benefit of the end user, usually to reduce page load time, and it’s generally infeasible for you to know all the considerations specific to every user.

The bit you can control is expiration time and no-cache behavior. These respectively specify that the user wants to refetch the resource because it is expected to have changed or should not be cached for other reasons.

Browsers may treat images differently than other resources (mainly differing in default expiration time when unspecified), but you can send HTTP headers for any resource.