How to Force a Refresh of Cached CSS Data: Query String vs. File Renaming?

How to Force Refresh of Cached CSS Data

When updating a website's CSS, browsers may continue to cache the outdated version, resulting in rendering issues. This article explores several methods to force a refresh of the cached CSS.

TL;DR

To resolve the caching issue, consider the following options:

• Modify the file name or query string
• Implement a change that occurs only once per release
• Favor file renaming over query string changes
• Set optimal HTTP headers to maximize caching benefits

In-Depth Analysis

What are We Trying to Achieve?
The ideal caching behavior involves fetching a new resource the first time it is requested and retrieving it from the local cache thereafter until it expires.

Observed Caching Behavior
To understand the caching behavior of browsers, a table summarizes various scenarios and their observed results.

Type	Cache Headers	Observed Result
Static filename	Expiration 1 Year	Taken from cache
Static filename	Expire immediately	Never caches
Static filename	None	HTTP 304 (not modified)
Static query string	Expiration 1 Year	HTTP 304 (not modified)
Static query string	Expire immediately	HTTP 304 (not modified)
Static query string	None	HTTP 304 (not modified)
Random query string	Expiration 1 Year	Never caches
Random query string	Expire immediately	Never caches
Random query string	None	Never caches

Type

Cache Headers

Observed Result

Static filename

Expiration 1 Year

Taken from cache

Static filename

Expire immediately

Never caches

Static filename

None

HTTP 304 (not modified)

Static query string

Expiration 1 Year

HTTP 304 (not modified)

Static query string

Expire immediately

HTTP 304 (not modified)

Static query string

None

HTTP 304 (not modified)

Random query string

Expiration 1 Year

Never caches

Random query string

Expire immediately

Never caches

Random query string

None

Never caches

Solution Options

Query String
Appending a random parameter to the CSS URL forces a new HTTP 200 request, but only during the initial encounter. Subsequent requests may still return 304s.

Path Modification
Creating a new path provides a more permanent solution. You can automate the process to rewrite the path with a version number or other identifier.

File Renaming
An alternative approach involves renaming the CSS files with each release, ensuring a fresh request when the updated paths are referenced in the HTML.

ConclusionBy implementing the suggested techniques, you can force a refresh of cached CSS data and ensure that your users receive the most up-to-date CSS updates without compromising the benefits of caching.

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