Cat next adds a link next to the watch button to go to a random page in a category. This category can be selected by using the configure cat next button (in the more section for vector). The category is stored as a cookie for a maximum of 30 days. When selecting a category you can also click Reset, clearing the category and removing the next link, or, if you are on a category page, use that category. The script does not work with the minerva skin. The source code is available to view.
Installation edit
Hint: It's much easier if you get ScriptInstaller, then navigate to User:Danski454/cat-next.js and click "Install" at the top.
To install, add importScript( 'User:Danski454/cat-next.js' ); // Backlink: [[User:Danski454/cat-next.js]] to your common.js.