We can open Script Debugger for any server-side script by clicking on the Open Script Debugger icon on top of the script field as shown here:
The debugger can be used only when the script is executed in an interactive session. It becomes active only for the current (logged-in) session and doesn't affect other logged-in sessions or users executing the same code. Furthermore, breakpoints set in one session don't affect other developers trying to debug the same code with their own set of breakpoints.
The GlideSystem method isInteractive() can be used to determine whether the script is running in interactive mode or not. If the return value is true then the script is in interactive mode. A user must have the script_debugger role granted and at least read-only access to the script in order to use Script Debugger to debug the code. The major part of this chapter is relevant to the latest version of ServiceNow --Istanbul.