How Effective Are URL Parameters for Cache Busting?

Cache Busting with URL Parameters

Caching is a crucial technique for optimizing website performance by storing frequently requested resources on a browser's local storage. However, when deploying changes to these resources, it is necessary to invalidate the cached copies to ensure that users access the updated versions. One simple approach to cache busting is appending a parameter to the end of CSS and JS file URLs.

Effectiveness of URL Parameters for Cache Busting

Appending a query parameter to a resource URL, such as "?v=1.123", effectively breaks the cache. The browser treats this parameter as a unique identifier and considers the resource as a new path. Therefore, it loads the resource from the server instead of retrieving it from the cache.

Caching Behavior with URL Parameters

Contrary to the concern that the URL parameter may prevent the browser from caching the response, the browser typically assumes that the source will remain the same for the same URL, even with the parameter. As a result, the browser caches the resource with the updated URL, including the query string.

When subsequent requests are made for the same URL, the browser retrieves the resource from the cache as long as the query parameter remains unchanged. This behavior ensures that the updated version of the resource remains cached until a new version is deployed with a different query parameter value, such as "?v=1.124".

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