I have to admit - I did not use the JSL Debugger till I set up my own Namespace Inspector.
Just to find out that it's already there ... The huge benefit compared my own one: it can even list variables from local namespaces of functions ... Ah no, it cant.

JMP 18.1
Names default to here(1);
z=1;
func = function({a},{c},
c=a*2;
c;
);
func(1);