However it's not convenient and creates unnecessary load on the WikiMedia servers. Also, it seems like these days Wikimedia servers are configured not to give out the saved .js version right away, so you have to wait some minute after saving and then [[Wikipedia:Bypass your cache|bypassing your browser cache]].
shahrooz (admin)
=== Local HTML file ===
* Save Wikipedia page to your local hard drive, including all corresponding .css and .js files. Specific details depend on your browser. <!--how-to might be nice-->
* Open saved page in your editor, insert your script code either between <code><script></script></code> tags or as a separate local file with <code><script src="file://C://you_local_path/name.js"></script></code>.
* Open saved page in your browser and preview the result.
This is a very traffic-wise way to quickly develop a user script. However, it has the following disadvantages:
* browser will not let you test Ajax queries from a local file
* you have to save different pages depending on what exactly page (history, etc.) is needed for testing
* you have to periodically re-save all .js files to synchronize with MediaWiki changes
* if you want to "casually" test the script while you're browsing Wikipedia, you still have to use other testing methods
