uses
  {...,} System.JSON;

procedure TForm1.Button1Click(Sender: TObject);
var
  s: string;
  i: Integer;
  js: TJSONObject;
begin
  s := '{"type1":199, "type2":"val2", "ar":["arval1","arval2"]}';
  js := TJSONObject.ParseJSONValue(s) as TJSONObject;
  for i := 0 to js.Count-1 do
    Memo1.Lines.Add(js.Pairs[i].JsonValue.ClassName);
end;

// Способ первый
uses
  {...,} System.JSON, REST.Json;

procedure TForm1.Button1Click(Sender: TObject);
var
  json: string;
begin
  json := '{"type1":199, "type2":"val2", "ar":["arval1","arval2"]}';
  ShowMessage(TJSON.Format(TJSONObject.ParseJSONValue(json)));
end;

// Способ второй
uses
  {...,} System.JSON;

procedure TForm1.Button1Click(Sender: TObject);
const
  DEF_INDENT = 4;
var
  json: string;
  jo: TJSONObject;
begin
  json := '{"type1":199, "type2":"val2", "ar":["arval1","arval2"]}';
  jo := TJSONObject.ParseJSONValue(json) as TJSONObject;
  ShowMessage(jo.Format(DEF_INDENT));
end;

// Или немного иначе
uses
  {...,} System.JSON;

procedure TForm1.Button1Click(Sender: TObject);
const
  DEF_INDENT = 4;
var
  json: string;
  jv: TJSONValue;
begin
  json := '{"type1":199, "type2":"val2", "ar":["arval1","arval2"]}';
  jv := TJSONObject.ParseJSONValue(json);
  try
    ShowMessage(jv.Format(DEF_INDENT));
  finally
    jv.Free;
  end;
end;