Well, apart from the Error Console that can be opened from the Develop menu (which in turn can be enabled in (Prefences / Advanced / Show Develop menu in menu bar) there aren’t many javascript debugging options in Safari AFAIK.
Still, the error console is quite useful as it shows javascript errors and also lets you to execute arbitrary Javascript statements.
Since you are on Windows anyway, you could try using the inbuilt Javascript debugger of Google Chrome, which is a browser very similar to Safari (although the Javascript engine is different).