There is no JavaScript debugging environment in current versions of PixInsight. I plan on including one when I change the current JavaScript engine, but don't hold your breath.
I completely agree with Rick. I use debuggers in very rare occasions. Actually, I cannot remember the last time I used one with PixInsight, probably many years ago. If you develop good programming practices, style and skills, then a debugger cannot tell you anything you don't know, except in very special cases. The key is having full control on your code, not the opposite.