How do you debug javascript in Safari?

not sure if in Windows is the same, but on the mac version you have a Developer menu ("Develop"), at the mac this menu is shown via the preferences > advanced > show develop menu, and there you can view items such as "Start debugging javascript".

EDIT: just found this: Enabling debug menu in Safari for Windows

Have you tried using the develop bar?

To enable, go to preferences -> Advanced -> Check show develop menu in the menu bar