Actually, it depends on what you mean by debugging, and there is stuff you can do to debug both...
In Spotfire version 7.0 and above, you have better debug printing than in previous versions. You can see the line number that caused the exception and a (limited) call stack. Other than that, you need to use print statements to show what's going on in the script.
And then copying and pasting the url into Chrome and start debugging with Developer Tools (F12)
Spotfire 7.5 has an option on the Tools menu that you can enable for debugging:
Developer tools in the Tools menu Tools for developers and power users can now be exposed in a new menu option:
Tools > Development.. Development Tools enables you to:
● Reload the browser user interface (Alt+Shift+Ctrl+F5).
● Launch the browser debugger (Alt+Shift+Ctrl+F12).
● Copy the URL.
To enable the Development Tools menu option, select Tools > Options, go to the Application page and select the Show development menu check box.