Descriptions of parameters after js css

When browsing some websites, we often see that js css with webpage links is always followed by some parameters. I checked them in detail today:

In this case, there are two main possibilities:

The script does not exist, but is dynamically generated on the server. A parameter is included to indicate the version number of the generated script file.

To speed up the response, some clients cache the corresponding js css. Therefore, each time the js css version is upgraded, the client browser automatically updates the new version of js or css.

The second case should be the most