type
  TForm1 = class(TForm)

  public

  published
    procedure DoJsCall(str:string);                                                    //必须声明方法为published
    function   DoJsCall2(str:string):Tobject;

  end;

  TProcedure = function(Param: string):Tobject of object;          //定义方法原型，方便调用

  Form1: TForm1;

procedure TForm1.DoJsCall(str: string);
begin
  mmo1.Lines.Add(str);
end;

function TForm1.DoJsCall2(str: string): Tobject;
begin
  mmo1.Lines.Add(str);
  Result := TObject(mmo1.Lines.Text);
end;

//根据方法名调用方法

function ExecuteMethod(Obj: TObject; Name, Param: string):Tobject;
var
  PMethod: TMethod;
  AProcedure: TProcedure;
begin
  PMethod.Data := Pointer(Obj);
  PMethod.Code := Obj.MethodAddress(Name);
  if Assigned(PMethod.Code) then
  begin
    AProcedure := TProcedure(PMethod);
    Result := AProcedure(Param);
  end;
end;

调用：

procedure TForm1.btnExecuteMethodClick(Sender: TObject);
var
  s : string;
begin
  mmo1.Text := '';
  ExecuteMethod(self ,'DoJsCall2','aaa');
  ShowMessage('Step1:'+mmo1.Text);
  s := PChar(ExecuteMethod(self ,'DoJsCall2','bbb'));
  ShowMessage('Step2:'+s);
end;