Why Are Parameters Added to CSS and JavaScript File Links?

Understanding the Purpose of Parameters in CSS and JavaScript Linking

Many websites append parameters to the source of their linked CSS and JavaScript files. This practice may seem unusual, as these files typically don't accept and process external parameters. However, this technique serves an important purpose.

Caching Prevention

The primary reason for passing parameters to CSS and JavaScript files is to prevent caching. Caching is a mechanism that browsers employ to store frequently accessed content locally, such as previously loaded files. While caching can improve performance, it can also lead to problems if a new version of a file is released but the browser continues to load the cached version.

By adding unique parameters to the link source, you force the browser to retrieve the file directly from the server, bypassing its cache. This ensures that users always receive the most recent version of your files, preventing them from viewing outdated or incorrect content.

Example

In the Stack Overflow source code, you mention this line:

<script type="text/javascript" src="http://sstatic.net/js/master.js?v=55c7eccb8e19"></script>

Here, the parameter "v=55c7eccb8e19" is appended to the end of the link source. This version parameter indicates that the version of the master.js file being loaded has the specified hash value. When the browser encounters this parameter, it requests the file directly from the server, ensuring that the most recent version is obtained.

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