Adding a function with var and default parameters

You don't need to care about default parameters - they are substituted automatically by FastScript. Var parameters must be handled by you.

  fsScript1.AddMethod('function DelphiFunc(var s: String; i: Integer = 0): Boolean', CallMethod); 

{ the method handler }
function TForm1.CallMethod(Instance: TObject; ClassType: TClass; const MethodName: String; 
  var Params: Variant): Variant; 
var
  s: String;
begin 
  s := Params[0];
  Result := DelphiFunc(s, Params[1]); 
  Params[0] := s;
end;