Use .class for instance RHS typecheck
Use .class for instance RHS typecheck

Avoid unnecessary (and actually incorrect) call to
Interpreter.prototype.isa() by checking .class === 'function' instead.

google/CodeCity,NeilFraser/CodeCity,google/CodeCity,NeilFraser/CodeCity,google/CodeCity,NeilFraser/CodeCity,NeilFraser/CodeCity,google/CodeCity