extendscript debugging with photoshop? is this possible?

Just starting to use ExtendScript (v3.8.0.12) to write a script for Photoshop CS6. 

When I run the script in ExtendScript I can an error "Result:undefined" when I hit the first line of code that references the current opened file in Photoshop.  e.g. " var Name = app.activeDocument.name.replace(/\.[^\.]+$/, ''); "

Question - Is there a way to "target" my photoshop runnining instance so when debugging in ExtendScript is uses this?