Visual Studio 2012 comes with the very nice Page Inspector. I like it! Problem though, I haven't found how (if?) I can turn on JavaScript debugging. Could someone point me in the right direction?
In IE9 (only one time): Tools > Internet Options > Advanced tab > In Browsing category > Clear "Disable script debugging" check boxes (both) > restart IE.
In VS 2012: Run the Page Inspector ( when javascript error box opens, click No ! )
Choose from VS menu: DEBUG > Attach to process...
Select "WebBrowserServer.exe" and click Attach
In Page Inspector window click the Refresh icon.
Debugging works pretty well, but it's one condition. Don't insert any breakpoints in your code (or clear them before - DEBUG > Delete All Breakpoints). There can cause a lot of problems - from hanging and frozing to entirely crashing your VS.