4.2 Optimize Browser Caching

Browser caching reduces the requirement for files to need to be constantly reloaded from the server, and in certain situations, it can even allow for files to be viewed offline (or in the case of a reverse proxy, send immediate recurring requests without additional calculation or computation from the server). As such, this will have sustainability and performance benefits (for instance by greatly reducing Time-To-First-Byte).

Criteria

Server-side Caching: If using a CMS, install an applicable plugin to enable on-the-fly server-side caching. Otherwise, use the provided server configuration files to include and tweak the file-type cache expiration using expires, bfcache, or cache-control HTTP header. If using a language or framework that generates pages on request, cache responses for static pages so that they can be reused for future visitors.
Offline Access: Client-side JavaScript uses a combination of ServiceWorkers, WebWorkers, storage Application Programming Interfaces (APIs), or cookies (if necessary) to streamline the user-journey. For example, through the use of a PWA (Progressive Web Application) to ensure that an offline version is available and accessible at all times to reduce inequality and improve accessibility.

Impact

High

Effort

High

Benefits

Social Equity:
Allows websites to be functional in regions where no or intermittent Internet connectivity is available.
Performance:
Unmodified files don’t need to constantly be redownloaded (saving bandwidth, and server-side caching reduces the amount of computing resources required (as fewer HTTP requests will likely be submitted). Also, being selective over cached content balances faster reloads over the need to request new pages, which means that visitors may experience less latency due to data being held for repeat requests.
Economic:
Reduced data transfer allows for savings for individuals on a monitored data plan and infrastructure costs for the provider.
Conversion:
Caching increases repeat visitor page-load speeds (a customer benefit).

GRI

materials: Medium
energy: High
water: Medium
emissions: High

Example

Code:
```
Expires:  Wed, 01 Jun 2023 08:00:00 GMT
```
HTTP expires headers can be used to control the response.

Resources

View the Guideline